# RME DigiCheck NG 0.93 Help

## General

DigiCheck NG provides a number of digital measuring functions ("instruments"), of which up to 4 can be arranged per window. With an RME audio interface you get a high quality audio analyzer with maximum variability.

These instruments are currently available:

Two Channel Level Meter
Multichannel Level Meter
Global Level Meter
Program Meters
Spectral Analyser
Vector Audio Scope
Totalyser
Surround View
Surround View w. R 128
R 128 Loudness Meter
Bitstatistics and Noise
Frequency Measurement
Oscilloscope
Spectroscope
Credits

A connection to other audio apps is not provided. With the loopback function of the RME interfaces, however, connections to outputs can be established and the signals output by other apps can be analyzed on the same computer.

DigiCheck NG only works with devices from RME.

## Operation

### Mouse

The black dividing lines between the instruments can be moved with the mouse. With the four-way layout you can bring the dividing lines together at one point and then slide them apart in any direction to get horizontally or vertically offset arrangements.

Starting with version 0.90 the display of most instruments is pixel-aligned, which results in improved display quality, but leads to jumps in the size of the elements (e.g. a Spectral Analyzer with 70dB range and 0.5dB resolution can only be resized in increments of 141 pixels in height).

By dragging with the mouse while holding down the left mouse button, instruments can be exchanged between the fields.

In some instruments there are switches that can be operated with a mouse click. In addition, a double click resets the hold values ​​on most instruments.

With a click of the right mouse button in an instrument, a context menu opens which contains the items of the Option Menu relevant for the instrument.

### Menu

#### Preferences (re-labled as "Settings" starting with Ventura)

The default values ​​for the font sizes can be set here. You can also specify which filter is to be used for the intersample peak determination ("TruePeak").

Historically, DigiCheck NG has used a filter that makes very good use of the coprocessors (ARM NEON; Intel SSE) and positions one of the additionally calculated samples in the middle between the input samples. Since an update to BS.1770, a specific filter has been recommended that behaves slightly differently and may show slightly lower values. Optionally, this filter can be selected in order to obtain exactly comparable results.

In the display options, you can set a preferred refresh rate in frames per second (fps). The implementation depends on the properties of the respective monitor/graphics chip combination. Whole parts of the refresh rate selected in the system settings of the monitor are technically possible, to which the default value is rounded off. A very high value (500fps) results in the highest possible refresh rate.

Higher refresh rates produce a smoother display (if the audio buffer size is small enough), but are associated with higher CPU and GPU loads. For simpler monitoring purposes, a lower rate with less system load can also be useful.

If "Show Frame Rate" is activated, the measured frame rate is displayed at the bottom right.

#### File

With these menu items new windows can be created and all settings can be saved or restored as a workspace.

#### Options – Enable Audio Processing

With this menu item the audio analysis is started or paused.

#### Options – Audio Device Setup

The menu item opens a dialogue box in which up to 3 RME audio interfaces can be configured for use with DigiCheck NG.

Sample rate and buffer size can be chosen for each interface. DigiCheck NG only sets the sample rate at the start of the audio analysis if the corresponding option "Set actively" has been set. Otherwise the currently active sample rate or the sample rate set by other programs is used.

The buffer size determines the latency that exists between a signal change and the display on the screen. Smaller values ​​lead to a lower delay, but have the disadvantage of a higher CPU load (because of the overhead when changing buffers more frequently) and a greater risk of samples being lost.

The "Add Playback Channels" option is only available for USB devices with driver 4.04 or later installed. Then the playback channels appear in the channel lists of the input selection of the instruments and are available for analysis. The buffer size should then not be set larger than 1024 samples for sample rates between 44.1 and 48k. At 32kHz, the playback data is only available if the respective playback program uses a maximum buffer size of 2048.

The settings in this dialogue have a global effect on all instruments. In the instruments Input Selection dialogue one of the interfaces configured here can be chosen as the input source.

#### Options – Instruments Layout

The arrangement of the fields in the window is selected from a list.

There is a background memory in the app that preserves the settings of instruments that are no longer visible when a layout with a smaller number of fields is selected. Nevertheless, it is advisable to save important settings as a preset beforehand when making such changes. Normally, after a short time, you will have created some arrangements for your typical use cases, which can be saved as workspaces and quickly restored.

#### Options – Instrument (i) – Type Selection

The instrument type for field (i) is selected from a list here. For better identification of the field, it is shown lighter.

#### Options – Instrument (i) – Input Selection

This menu item opens a dialogue for selecting the inputs of the respective instrument. A pre configured audio interface can be selected in the upper part.

Below is a list with the input channels of the respective instrument, each of which can be assigned a channel of the audio interface.

With certain instruments, individual channels can be deactivated and spaces can be added to the display (“space” option).

The Default Button resets the assignment to the channel scheme of the audio interface, Incremental fills the list continuously with the channels of the interface, starting with the channel set in the top line.

For the Global Level Meter and activated analysis of the playback channels, the respective channel range (or both) can be selected via the "Inputs" and "Playbacks" options. The total number of channels is limited to 200.

Both the audio interface and the channel selection are stored on the basis of indices. Therefore, e.g. a change of Audio Device 1 in the audio device setup will take effect for all instruments while retaining the channel numbers.

#### Options – Instrument (i) – Settings

A list with the parameters of the respective instrument is displayed. The adjustment of parameters takes effect immediately.

For instruments that consist of several sub-functions, the list is structured accordingly.

In the lower part there are buttons for selecting presets. The current settings of the instrument can be saved or loaded with it. Default resets to typical values.

If you exit the dialogue with Cancel, the changes made since opening (after a prompt) are canceled.

#### Options – Instrument (i) – Appearance

The parameters in the dialogue configure the display of the instrument. Font sizes and a heading can currently be set. The font size "Large" for "Results" is only effective for the tables in Totalyser and R128-Meter.

#### Options – Prevent Sleep

Activating this menu item prevents the computer from being idle. The function can be restricted by higher-priority interventions of the operating system.

#### Options – Use directly connected GPU

On computers with several graphics chips (GPU), only one GPU is connected to the monitor. With laptops etc. this is the graphics chip in the CPU so that the additional GPU can be deactivated to save energy. For DigiCheck NG, the operating system usually chooses the more powerful, dedicated GPU. However, this can have disadvantages (real higher GPU load on both GPUs due to the required transfer of pixel data; higher power consumption due to activation of the dedicated GPU chip). So if the graphics performance of the internal GPU is sufficient (depending on other programs, number of windows and size), you should activate this option.

#### View – Interface Statistics

A window opens with status information on the audio interfaces used. The window can remain open independently of the analyzer windows (listed in the "Windows" menu).

- Sample Rate – shows the active sample rate, or a line if audio processing is deactivated in DigiCheck.
- Load – shows the runtime of all analysis functions in relation to the available time (buffer size by sample rate) in percent. The overall CPU load that DigiCheck NG causes cannot be deduced from this, because graphics output etc. have to be added.
- Missed – shows the number of samples "lost" for the analysis. For a continuously exact analysis the value must be 0. Causes for lost samples can be too small selected buffer size, too high CPU load by other programs or the operating system as well as a too extensive setup of the audio analysis in DigiCheck NG for the respective CPU.
- Reset – resets the lost samples counter.

## Instruments

### Two Channel Level Meter

This instrument measures the signal levels of 2 channels. Peak, optionally inter sample peak (true peak), RMS with DC or RLB filter are calculated. In addition, various markers for peak hold and RMS with a long integration time are available. All of this can be configured using numerous options.

In addition to the setting parameters of the standard level meter, the Two Channel Level Meter has the option of displaying the RMS levels in separate bars and displaying a phase meter.

Setting parameters

- Show Phase Meter – activates a phase meter below the meter bars.
- Phase Meter Int. Time – controls the integration time and thus the reaction rate of the phase meter. The higher the value, the longer past signal components are included in the calculation and the display slows down.
- Show RMS Bars – switches to a 4-bar display with separated RMS bars.
- Reference Level – defines the offset between displayed level and digital full scale in dB. With a setting of e.g. -12dB, the display value "0dB" is shifted to -12dB full scale. In other words, a headroom of 12dB to digital full scale is inserted into the displayed value.
- Top Level (vs. FSC) – sets the upper end of the level meter in relation to digital full scale. This setting is only available for linear scales, not for "Compressed Scale".
- Switch Level Red – above this level the red part of the bar begins.
- Switch Level Yellow – same for the yellow part.
- Bottom Level – defines the lower end of the display area. Available for linear scale only.
- Release Speed​ – determines the release speed of the bars. This also affects RMS and RMS slow calculation.
- Compressed Scale – switches the scaling to a non-linear dB scale, which has a fixed display range with 0dB full scale as top level. If the reference level is set lower than 0dB, the display range includes positive values. The top and bottom level parameters cannot be set with Compressed Scale. If Intersample Peaks ("True Peak") is activated, the display range is extended by 3dB.
- Text Level – allows you to choose which value should be displayed as text above the bars. The text display is only active if there is enough space in the width.
- Bar Level – selects the measurement value for the bars (RMS or peak).
- Peak Hold Time – defines the time for which the hold markers should be held after an update (higher or equal value).
- Infinite Hold Marker – activates an additional marker that remains at the highest peak value. The reset is done manually with Infinite Hold Reset or double click.
- Infinite Hold Reset – resets the permanent hold.
- FSC Count for OVR – specifies the number of full scale samples that must have occurred in succession before the peak display shows "OVR". The hexadecimal value 0x7FFF00 counts as full scale, so that 16-bit signals can also trigger an OVR
- Intersample Peak (TP) – activates an oversampling filter which calculates further points in the signal curve between received samples. With compressed music, these samples can go beyond the digital "full scale" (imaginable as an outwardly curved connecting line between 2 full-scale samples) and thus leading to overloads in downstream devices (D/A converter, sample rate converter, etc.). This function, also often referred to as "True Peak", increases the display range of the peak meter. For reference levels above -10dB, the display range is therefore extended upwards by 3dB. The OVR determination using full-scale samples is switched off. Instead, the peak markers above 0dB full scale are displayed in white.
- RMS + 3dB – enables the alignment of the display values ​​of RMS and peak. Mathematically, the RMS for a sinusoidal signal is 3dB lower than the peak value due to the quadratic mean value calculation, which leads to a poorer readability of the meters without this option.
- RMS Slow Marker – activates a marker based on an RMS calculation with a very long time constant. This enables the reading of weakly variable values ​​with high accuracy (also as numerical value in text level) or the estimation of the energy (volume) of dynamic signals.
- RMS RLB Filter – the RLB filter is a weighting filter from the context of loudness measurement (ITU BS.1770) and enables an improved mapping of loudness in RMS measurements. It significantly attenuates the signals in the bass range. The option only affects the RMS value.
- K-System – configures the level meters according to the specifications of the legendary mastering engineer Bob Katz. The setting is selected by the reference value (headroom) and affects various parameters for scaling, color switching, true peak, etc., which can no longer be set manually when the K-System is activated. Their previous settings are saved in the background.
- Show Pair Difference - enables an indicator of level difference between the channels. The difference between the RMS or RMS Slow values is shown, not the level of the differential signal (which can be different due to phase effects). The indicator can be used to monitor the balance of stereo channels or, with appropriate channel assignment, to evaluate input/output ratio.
- Diff. Indicator Range – sets indicator display range.

### Multichannel Level Meter

This instrument displays the signal levels of numerous channels (up to 32). The number and arrangement of channels can be freely determined. Gaps can be configured to improve readability.

Setting parameters

- Input Channel Count – defines the basic channel number of the Multichannel Level Meter
- Show Channel Names – changes the legend below bars to display the (shortened) channel names of the audio interface input channels. Otherwise channel numbers are displayed.
- Reference Level – defines the offset between displayed level and digital full scale in dB. With a setting of e.g. -12dB, the display value "0dB" is shifted to -12dB full scale. In other words, a headroom of 12dB to digital full scale is inserted into the displayed value.
- Top Level (vs. FSC) – sets the upper end of the level meter in relation to digital full scale. This setting is only available for linear scales, not for "Compressed Scale".
- Switch Level Red – above this level the red part of the bar begins.
- Switch Level Yellow – same for the yellow part.
- Bottom Level – defines the lower end of the display area. Available for linear scale only.
- Release Speed​ – determines the release speed of the bars. This also affects RMS and RMS slow calculation.
- Compressed Scale – switches the scaling to a non-linear dB scale, which has a fixed display range with 0dB full scale as top level. If the reference level is set lower than 0dB, the display range includes positive values. The top and bottom level parameters cannot be set with Compressed Scale. If Intersample Peaks ("True Peak") is activated, the display range is extended by 3dB.
- Text Level – allows you to choose which value should be displayed as text above the bars. The text display is only active if there is enough space in the width.
- Bar Level – selects the measurement value for the bars (RMS or peak).
- Peak Hold Time – defines the time for which the hold markers should be held after an update (higher or equal value).
- Infinite Hold Marker – activates an additional marker that remains at the highest peak value. The reset is done manually with Infinite Hold Reset or double click.
- Infinite Hold Reset – resets the permanent hold.
- FSC Count for OVR – specifies the number of full scale samples that must have occurred in succession before the peak display shows "OVR". The hexadecimal value 0x7FFF00 counts as full scale, so that 16-bit signals can also trigger an OVR
- Intersample Peak (TP) – activates an oversampling filter which calculates further points in the signal curve between received samples. With compressed music, these samples can go beyond the digital "full scale" (imaginable as an outwardly curved connecting line between 2 full-scale samples) and thus leading to overloads in downstream devices (D/A converter, sample rate converter, etc.). This function, also often referred to as "True Peak", increases the display range of the peak meter. For reference levels above -10dB, the display range is therefore extended upwards by 3dB. The OVR determination using full-scale samples is switched off. Instead, the peak markers above 0dB full scale are displayed in white.
  Activating this option increases the CPU load, especially with a high number of channels.
- RMS + 3dB – enables the alignment of the display values ​​of RMS and peak. Mathematically, the RMS for a sinusoidal signal is 3dB lower than the peak value due to the quadratic mean value calculation, which leads to a poorer readability of the meters without this option.
- RMS Slow Marker – activates a marker based on an RMS calculation with a very long time constant. This enables the reading of weakly variable values ​​with high accuracy (also as numerical value in text level) or the estimation of the energy (volume) of dynamic signals.
- RMS RLB Filter – the RLB filter is a weighting filter from the context of loudness measurement (ITU BS.1770) and enables an improved mapping of loudness in RMS measurements. It significantly attenuates the signals in the bass range. The option only affects the RMS value.
- K-System – configures the level meters according to the specifications of the legendary mastering engineer Bob Katz. The setting is selected by the reference value (headroom) and affects various parameters for scaling, color switching, true peak, etc., which can no longer be set manually when the K-System is activated. Their previous settings are saved in the background.
- Horizontal Meter - switches display to horizontal bars.
- Show Pair Difference - enables indicators of level difference between 2 channels. The difference between the RMS or RMS Slow values is shown, not the level of the differential signal (which can be different due to phase effects). The indicators can be used to monitor the balance of stereo channels or, with appropriate channel assignment, to evaluate input/output ratios.
- Diff. Indicator Range – sets indicator display range.

### Global Level Meter

Similar to the Multichannel Level Meter, the levels of numerous channels are displayed, but the number and arrangement of channels follows the audio interface. Gaps can be configured to improve readability.

Setting parameters

- Show Channel Names – changes the legend below bars to display the (shortened) channel names of the audio interface input channels. Otherwise channel numbers are displayed.
- Reference Level – defines the offset between displayed level and digital full scale in dB. With a setting of e.g. -12dB, the display value "0dB" is shifted to -12dB full scale. In other words, a headroom of 12dB to digital full scale is inserted into the displayed value.
- Top Level (vs. FSC) – sets the upper end of the level meter in relation to digital full scale. This setting is only available for linear scales, not for "Compressed Scale".
- Switch Level Red – above this level the red part of the bar begins.
- Switch Level Yellow – same for the yellow part.
- Bottom Level – defines the lower end of the display area. Available for linear scale only.
- Release Speed​ – determines the release speed of the bars. This also affects RMS and RMS slow calculation.
- Compressed Scale – switches the scaling to a non-linear dB scale, which has a fixed display range with 0dB full scale as top level. If the reference level is set lower than 0dB, the display range includes positive values. The top and bottom level parameters cannot be set with Compressed Scale. If Intersample Peaks ("True Peak") is activated, the display range is extended by 3dB.
- Text Level – allows you to choose which value should be displayed as text above the bars. The text display is only active if there is enough space in the width.
- Bar Level – selects the measurement value for the bars (RMS or peak).
- Peak Hold Time – defines the time for which the hold markers should be held after an update (higher or equal value).
- Infinite Hold Marker – activates an additional marker that remains at the highest peak value. The reset is done manually with Infinite Hold Reset or double click.
- Infinite Hold Reset – resets the permanent hold.
- FSC Count for OVR – specifies the number of full scale samples that must have occurred in succession before the peak display shows "OVR". The hexadecimal value 0x7FFF00 counts as full scale, so that 16-bit signals can also trigger an OVR
- Intersample Peak (TP) – activates an oversampling filter which calculates further points in the signal curve between received samples. With compressed music, these samples can go beyond the digital "full scale" (imaginable as an outwardly curved connecting line between 2 full-scale samples) and thus leading to overloads in downstream devices (D/A converter, sample rate converter, etc.). This function, also often referred to as "True Peak", increases the display range of the peak meter. For reference levels above -10dB, the display range is therefore extended upwards by 3dB. The OVR determination using full-scale samples is switched off. Instead, the peak markers above 0dB full scale are displayed in white.
  Activating this option increases the CPU load, especially with a high number of channels.
- RMS + 3dB – enables the alignment of the display values ​​of RMS and peak. Mathematically, the RMS for a sinusoidal signal is 3dB lower than the peak value due to the quadratic mean value calculation, which leads to a poorer readability of the meters without this option.
- RMS Slow Marker – activates a marker based on an RMS calculation with a very long time constant. This enables the reading of weakly variable values ​​with high accuracy (also as numerical value in text level) or the estimation of the energy (volume) of dynamic signals.
- RMS RLB Filter – the RLB filter is a weighting filter from the context of loudness measurement (ITU BS.1770) and enables an improved mapping of loudness in RMS measurements. It significantly attenuates the signals in the bass range. The option only affects the RMS value.
- K-System – configures the level meters according to the specifications of the legendary mastering engineer Bob Katz. The setting is selected by the reference value (headroom) and affects various parameters for scaling, color switching, true peak, etc., which can no longer be set manually when the K-System is activated. Their previous settings are saved in the background.
- Horizontal Meter - switches display to horizontal bars.
- Show Pair Difference - enables indicators of level difference between 2 channels. The difference between the RMS or RMS Slow values is shown, not the level of the differential signal (which can be different due to phase effects). The indicators can be used to monitor the balance of stereo channels or, with appropriate channel assignment, to evaluate input/output ratios.
- Diff. Indicator Range – sets indicator display range.

### Program Meters

Program meters in their final stage will include various vintage level meters.

Currently a VU meter (volume unit) is realized based on the model of mechanical level meters with a 300ms integration time constant and a germanium diode rectifier. The displayed level is comparable to RMS or loudness meters, so that a large headroom is required for leveling according to these display values. To avoid overloading with peak levels that are too high, there is an optional peak indicator with an LED. It works with oversampling to detect any level peaks between the samples.

Another variant is a "Quasi Peak Programme Meter", which implements a peak measurement with a slight rise limit (10ms for 90% display value) and runs down at 20dB in 1.5s. This meter works with oversampling and also has the above-mentioned optional peak LED.
The rise and fall time constants lead to a measured value that is slightly below 0dB at full scale for sinusoidal signals. This difference is corrected to a 0dB display value in this meter.

Setting parameters

- Meter Type – selection of the variant, currently VU and Quasi Peak.
- Channel Count – Number of channels (meters) in the instrument. If no active channel is available for a meter due to device properties, sample rate or channel selection, the meter is displayed without a level.
- Line Count – Number of lines on which the meters should be arranged.
- Motion Blur – controls an optional motion blur of the pointer to improve the visual effect.
- Show Peak Indicator – switches on the peak LED in the upper right area of ​​the meters.
- Switch Level Red vs. Reference – specifies the level for switching the LED to red compared to 0dB display value. Since 0dB corresponds to the reference level, this results in reference level + switch level in relation to digital full scale (e.g. -10dB reference level and 6dB switch level result in switching at -4dB full scale).
- Switch Level Yellow vs. Reference – indicates the level for switching the LED to yellow compared to 0dB display value.
- Peak Hold Time – hold time of the peak LED after leaving the switch level.

### Spectral Analyzer

This instrument consists of a filter bank that separates the signals in time domain and determines the level for each frequency range with a quasi-peak detector. Time constants for rise and fall are adjustable. A short rise time results in a fast peak determination, slower settings lead to a more energetic evaluation. That can be used, for example, for frequency response measurement.

The two input channels can be evaluated individually (left or right), summed up (mono component), subtracted (stereo component) or simultaneously, with the maximum being displayed.

In addition to various display options, there is also a switchable function that automatically adapts the upper end of the display range to the signal.

A special feature is the afterglow function, with which information about the temporal progress can be read.

The bands form a 1/3 octave arrangement. White noise results in a decreasing level for the bands with decreasing frequency, because the passband becomes narrower and thus the energy becomes lower. In the case of pink noise, the spectral energy and the respective pass band balance each other out, so that a straight line is created. The lowest band (20Hz) can optionally include the DC range and then shows a higher level in the case of noise.

Setting parameters

- Channel Select – controls the mode of evaluating the input channels. Left, right, sum and difference can be selected. Further maximum L/R, where both channels are analyzed in parallel in order to display the maximum of the levels.
- Top Level – indicates the upper end of the display range, selectable in 10dB steps.
- Enable Auto Range – activates the automatic adjustment of the upper end of the display range (top level) to the signal level.
- Display Range – the display range of the analyzer that can be set in several stages.
- Display Resolution – Selection of the step-size for one element ("LED") in dB.
- Hide Ultrasonic Bands – switches off the bands above 20kHz that are otherwise displayed at higher sample rates.
- Release Time – controls the return speed of the quasi-peak detection. A larger time constant results in a slower rewind.
- Rise Time – sets the rate of rise of the quasi-peak detector. A smaller time constant allows the display to follow short signal peaks. Larger time constants, also in connection with a longer release time, lead to a stronger integration of the signal curve.
- Display Mode – basic display mode. Points can be selected for a pure point display of the current level in the respective frequency band, with Bar the LEDs below this level also light up. Peak Hold activates a marker to display the previous maximum level.
- Peak Hold Time – is the time span over which a peak value should be held (if Infinite Hold is not activated).
- Infinite Hold – sets the hold time in peak hold mode to infinity. The hold values ​​are reset manually with a double click.
- Phosphorescence – activates afterglow of the display over a selectable period of time or permanently (infinite). With Infinite the reset is done by double clicking in the display field.

### Vector Audio Scope

The Vector Audio Scope (also known as "goniometer" in German-speaking countries) is an X-Y display rotated by 45° with an afterglow function. Without automatic gain control the resulting display area is a rhombus. If both channels have exactly the same signal (mono on 2 channels), the left-right deflection is canceled out and a vertical line is created, with a length determined by the level. If the signal of one channel is smaller, the line tilts in the direction of the other channel, up to a diagonal line when only one channel is active.

If there are "real" stereo signals, the display expands.

A lot of information can be read from this display, for example the strength of the compression (recognizable by the visible rhombus outline, to which the signals are limited), phase problems, balance errors etc.

Optionally, an automatic gain can be activated: If the input signal is smaller than the display area, the amplification is slowly increased. If the display area is exceeded by larger signals, the gain is reduced very quickly. This option has the advantage that smaller signals are better to read, but the fixed level reference is lost. The display area expands to the complete square.

Setting parameters

- Release Time – determines the afterglow time of the display. Small values ​​limit the display range to signals that were recently in the past, larger values ​​lead to the display of signals from a larger time range.
- Decode M/S – switches on an M/S decoder for corresponding microphone arrangements.
- X/Y Mode – activates a mode in which the left channel controls the X deflection and the right channel the Y deflection. This means that the display is no longer a goniometer in the strict sense.
- Enable Auto Gain – activates an automatic gain, which is increased depending on the set rise time, as long as a signal is present and this does not fill the display range. In the event of a higher input signal that would exceed the display range, the gain is reduced without delay.
- Rise Time AGC – sets the increase in gain when the auto gain function is active.
- Show Phase Meter – activates a phase meter below the Vector Audio Scope display.
- Phase Meter Int. Time – controls the integration time and thus the reaction rate of the phase meter. The higher the value, the longer past signal components are included in the calculation and the display slows down.

### Totalyser

The "Totalyser" shows Spectral Analyzer, Two Channel Level Meter and Vector Audio Scope in one instrument. In addition, the numerical values for RMS, peak and correlation (phase) are displayed in an enlarged field.

The setting parameters are described in the respective instruments.

### Surround View

In a circular representation, the RMS levels of the channels of the surround setup span a figure from which the height and the ratio of the volumes can be read off very well. Optionally, a weighting filter from the R 128 Meter (RLB and ITU) can be switched on in order to achieve a better representation of the human loudness perception. The low frequency effect channel is displayed as a subordinate circle. No weighting or DC filter is applied to this channel, as this would reduce the display value too much in the bass range.

Phase meters for the relevant channel pairs are optionally displayed below the figure, further level meters for the individual channels.

In the input selection menu, unused channels can be switched off so that the displayed figure is not distorted.

Setting parameters Surround View

- Reference Level – sets a reference level that is displayed as a circle and forms the 0dB starting position for the scaling marks. With this setting, which is independent of the reference of the level meters, a suitable target value for the RMS level (loudness) can be selected.
- Top Level (vs. FSC) – sets the highest displayable level in relation to full scale. This means that the display can be effectively enlarged for smaller (RMS) levels.
- Integration Time – specifies the time constant for the RMS calculation. Smaller values ​​result in a faster display, larger values ​​integrate more strongly.
- Weighting Filter – optionally switches on the filters known from ITU BS.1770, which bring about a better mapping of the loudness by simulating the hearing sensitivity (RLB filter for Bass cut, complete ITU filter with additional treble boost).
- Compressed Scale – switches to a compressed display for lower levels. The visible 10dB level markers are accordingly closer inside the circle.
- Show LFE Circle – activates the red circle display for the level of the Low Frequency Effect channel.
- Show Phase Meters – controls the display of the phase meters for the relevant channel pairs below the surround view display.
- Phase Meter Int. Time – controls the integration time and thus the reaction rate of the phase meter. The higher the value, the longer past signal components are included in the calculation and the display slows down.
- Show Pair Difference - enables indicators of level difference between 2 channels. The difference between the RMS or RMS Slow values is shown, not the level of the differential signal (which can be different due to phase effects). The indicators can be used to monitor the balance of stereo channels.
- Diff. Indicator Range – sets indicator display range.

Setting parameters Level Meters

- Reference Level – defines the offset between displayed level and digital full scale in dB. With a setting of e.g. -12dB, the display value "0dB" is shifted to -12dB full scale. In other words, a headroom of 12dB to digital full scale is inserted into the displayed value.
- Top Level (vs. FSC) – sets the upper end of the level meter in relation to digital full scale. This setting is only available for linear scales, not for "Compressed Scale".
- Switch Level Red – above this level the red part of the bar begins.
- Switch Level Yellow – same for the yellow part.
- Bottom Level – defines the lower end of the display area. Available for linear scale only.
- Release Speed​ – determines the release speed of the bars. This also affects RMS and RMS slow calculation.
- Compressed Scale – switches the scaling to a non-linear dB scale, which has a fixed display range with 0dB full scale as top level. If the reference level is set lower than 0dB, the display range includes positive values. The top and bottom level parameters cannot be set with Compressed Scale. If Intersample Peaks ("True Peak") is activated, the display range is extended by 3dB.
- Text Level – allows you to choose which value should be displayed as text above the bars. The text display is only active if there is enough space in the width.
- Bar Level – selects the measurement value for the bars (RMS or peak).
- Peak Hold Time – defines the time for which the hold markers should be held after an update (higher or equal value).
- Infinite Hold Marker – activates an additional marker that remains at the highest peak value. The reset is done manually with Infinite Hold Reset or double click.
- Infinite Hold Reset – resets the permanent hold.
- FSC Count for OVR – specifies the number of full scale samples that must have occurred in succession before the peak display shows "OVR". The hexadecimal value 0x7FFF00 counts as full scale, so that 16-bit signals can also trigger an OVR
- Intersample Peak (TP) – activates an oversampling filter which calculates further points in the signal curve between received samples. With compressed music, these samples can go beyond the digital "full scale" (imaginable as an outwardly curved connecting line between 2 full-scale samples) and thus leading to overloads in downstream devices (D/A converter, sample rate converter, etc.). This function, also often referred to as "True Peak", increases the display range of the peak meter. For reference levels above -10dB, the display range is therefore extended upwards by 3dB. The OVR determination using full-scale samples is switched off. Instead, the peak markers above 0dB full scale are displayed in white.
- RMS + 3dB – enables the alignment of the display values ​​of RMS and peak. Mathematically, the RMS for a sinusoidal signal is 3dB lower than the peak value due to the quadratic mean value calculation, which leads to a poorer readability of the meters without this option.
- RMS Slow Marker – activates a marker based on an RMS calculation with a very long time constant. This enables the reading of weakly variable values ​​with high accuracy (also as numerical value in text level) or the estimation of the energy (volume) of dynamic signals.
- RMS RLB Filter – the RLB filter is a weighting filter from the context of loudness measurement (ITU BS.1770) and enables an improved mapping of loudness in RMS measurements. It significantly attenuates the signals in the bass range. The option only affects the RMS value.
- K-System – configures the level meters according to the specifications of the legendary mastering engineer Bob Katz. The setting is selected by the reference value (headroom) and affects various parameters for scaling, color switching, true peak, etc., which can no longer be set manually when the K-System is activated. Their previous settings are saved in the background.
- Show Pair Difference - enables indicators of level difference between 2 channels. The difference between the RMS or RMS Slow values is shown, not the level of the differential signal (which can be different due to phase effects). The indicators can be used to monitor the balance of stereo channels.
- Diff. Indicator Range – sets indicator display range.

### Surround View w. R 128

This instrument offers a combination of surround view and R 128 Meter.

Setting parameters Surround View

- Reference Level – sets a reference level that is displayed as a circle and forms the 0dB starting position for the scaling marks. With this setting, which is independent of the reference of the level meters, a suitable target value for the RMS level (loudness) can be selected.
- Top Level (vs. FSC) – sets the highest displayable level in relation to full scale. This means that the display can be effectively enlarged for smaller (RMS) levels.
- Integration Time – specifies the time constant for the RMS calculation. Smaller values ​​result in a faster display, larger values ​​integrate more strongly.
- Weighting Filter – optionally switches on the filters known from ITU BS.1770, which bring about a better mapping of the loudness by simulating the hearing sensitivity (RLB filter for Bass cut, complete ITU filter with additional treble boost).
- Compressed Scale – switches to a compressed display for lower levels. The visible 10dB level markers are accordingly closer inside the circle.
- Show LFE Circle – activates the red circle display for the level of the Low Frequency Effect channel.
- Show Phase Meters – controls the display of the phase meters for the relevant channel pairs below the surround view display.
- Phase Meter Int. Time – controls the integration time and thus the reaction rate of the phase meter. The higher the value, the longer past signal components are included in the calculation and the display slows down.

Setting parameters Level Meters

- Reference Level – defines the offset between displayed level and digital full scale in dB. With a setting of e.g. -12dB, the display value "0dB" is shifted to -12dB full scale. In other words, a headroom of 12dB to digital full scale is inserted into the displayed value.
- Top Level (vs. FSC) – sets the upper end of the level meter in relation to digital full scale. This setting is only available for linear scales, not for "Compressed Scale".
- Switch Level Red – above this level the red part of the bar begins.
- Switch Level Yellow – same for the yellow part.
- Bottom Level – defines the lower end of the display area. Available for linear scale only.
- Release Speed​ – determines the release speed of the bars. This also affects RMS and RMS slow calculation.
- Compressed Scale – switches the scaling to a non-linear dB scale, which has a fixed display range with 0dB full scale as top level. If the reference level is set lower than 0dB, the display range includes positive values. The top and bottom level parameters cannot be set with Compressed Scale. If Intersample Peaks ("True Peak") is activated, the display range is extended by 3dB.
- Text Level – allows you to choose which value should be displayed as text above the bars. The text display is only active if there is enough space in the width.
- Bar Level – selects the measurement value for the bars (RMS or peak).
- Peak Hold Time – defines the time for which the hold markers should be held after an update (higher or equal value).
- Infinite Hold Marker – activates an additional marker that remains at the highest peak value. The reset is done manually with Infinite Hold Reset or double click.
- Infinite Hold Reset – resets the permanent hold.
- FSC Count for OVR – specifies the number of full scale samples that must have occurred in succession before the peak display shows "OVR". The hexadecimal value 0x7FFF00 counts as full scale, so that 16-bit signals can also trigger an OVR
- Intersample Peak (TP) – activates an oversampling filter which calculates further points in the signal curve between received samples. With compressed music, these samples can go beyond the digital "full scale" (imaginable as an outwardly curved connecting line between 2 full-scale samples) and thus leading to overloads in downstream devices (D/A converter, sample rate converter, etc.). This function, also often referred to as "True Peak", increases the display range of the peak meter. For reference levels above -10dB, the display range is therefore extended upwards by 3dB. The OVR determination using full-scale samples is switched off. Instead, the peak markers above 0dB full scale are displayed in white.
- RMS + 3dB – enables the alignment of the display values ​​of RMS and peak. Mathematically, the RMS for a sinusoidal signal is 3dB lower than the peak value due to the quadratic mean value calculation, which leads to a poorer readability of the meters without this option.
- RMS Slow Marker – activates a marker based on an RMS calculation with a very long time constant. This enables the reading of weakly variable values ​​with high accuracy (also as numerical value in text level) or the estimation of the energy (volume) of dynamic signals.
- RMS RLB Filter – the RLB filter is a weighting filter from the context of loudness measurement (ITU BS.1770) and enables an improved mapping of loudness in RMS measurements. It significantly attenuates the signals in the bass range. The option only affects the RMS value.
- K-System – configures the level meters according to the specifications of the legendary mastering engineer Bob Katz. The setting is selected by the reference value (headroom) and affects various parameters for scaling, color switching, true peak, etc., which can no longer be set manually when the K-System is activated. Their previous settings are saved in the background.
- Show Pair Difference - enables indicators of level difference between 2 channels. The difference between the RMS or RMS Slow values is shown, not the level of the differential signal (which can be different due to phase effects). The indicators can be used to monitor the balance of stereo channels.
- Diff. Indicator Range – sets indicator display range.

Setting parameters R 128 Meter

- Predefined Scale – allows the selection of the two scales recommended by the EBU with 9dB and 18dB top level. The reference (0LU) is set to -23LUFS. The selection "OFF" switches to the settings of the normal level meters of the respective instrument, including Reference Level.
- Momentary Marker – switches on a peak hold marker for the momentary display, optionally with an infinite hold time (reset by double click).
- Short Term Marker – configures a marker in the short term display, either peak hold or slow for additional integration of the display value.
- Show M&S Bars only – switches off the integrated value bar and the text field so that only momentary and short term values are displayed.

### R 128 Loudness Meter

This instrument implements the loudness determination procedure that was first described in EBU recommendation R 128 and is now defined in terms of signal processing under ITU-R BS.1770-4. Put simply, after filtering in the frequency range, which is intended to simulate the human loudness perception, an RMS determination is carried out in 400 ms time windows. The RMS value (root mean square value) depicts the energy of the signals in the individual channels, which is summed up in a weighted manner for multi-channel measurements according to a specified scheme. The resulting measured value for 400ms is displayed as "momentary loudness" (M). Summarized over a period of 3s, this results in “short-term loudness” (S). For measurements over a longer period of time, e.g. a recording, BS.1770 prescribes a statistical evaluation procedure that leads to "(program) integrated loudness" (I).

In principle, the results are available in decibels, which are referred to in the documents mentioned as Loudness Units ("LU"). These can refer to digital full-scale ("LUFS") or to an arbitrarily set reference point (-23.0LUFS for 0.0LU for EBU, -14LUFS recommended for Spotify). The EBU recommends additionally 2 scales, which can be selected as an option.

The “integrated loudness” over a period of time needs a start and an end. The green start / stop button in the instrument serves for this purpose. According to the above documents, a gate works internally, which only enables time windows with a minimum signal level for the calculation. So you can start the measurement at any time, then play back the recording and stop the measurement when it is over. The effective measuring time is displayed in the instrument ("Gated Time"), in addition to the duration of activation by the green button ("Total Time"). The red button resets the stored values ​​before or during a measurement.

Parallel to the measurement of the "integrated loudness", a statistical method determines the dynamic range, called the "loudness range" LRA.

The recommendations mentioned also include an inter-sample peak determination. For this purpose, the curve shape between the samples is calculated at several points via a digital filter and used for the peak display. With specially generated test signals, the result can be several decibels above full-scale, with highly compressed music up to 1dB can be observed.

With RME DigiCheck, the inter sample peak determination can optionally be switched on for all level meters. Historically, a filter is used that makes very good use of the coprocessors (ARM NEON; Intel SSE) and positions one of the additionally calculated samples in the middle between the input samples. Since an update to BS.1770, a specific filter has been recommended that behaves slightly differently and, under certain circumstances, shows values ​​that are a little lower. This filter can optionally be selected in the Preferences menu in order to obtain exactly comparable results.

Setting parameters Level Meters

- Reference Level – defines the offset between displayed level and digital full scale in dB. With a setting of e.g. -12dB, the display value "0dB" is shifted to -12dB full scale. In other words, a headroom of 12dB to digital full scale is inserted into the displayed value.
- Top Level (vs. FSC) – sets the upper end of the level meter in relation to digital full scale. This setting is only available for linear scales, not for "Compressed Scale".
- Switch Level Red – above this level the red part of the bar begins.
- Switch Level Yellow – same for the yellow part.
- Bottom Level – defines the lower end of the display area. Available for linear scale only.
- Release Speed​ – determines the release speed of the bars. This also affects RMS and RMS slow calculation.
- Compressed Scale – switches the scaling to a non-linear dB scale, which has a fixed display range with 0dB full scale as top level. If the reference level is set lower than 0dB, the display range includes positive values. The top and bottom level parameters cannot be set with Compressed Scale. If Intersample Peaks ("True Peak") is activated, the display range is extended by 3dB.
- Text Level – allows you to choose which value should be displayed as text above the bars. The text display is only active if there is enough space in the width.
- Bar Level – selects the measurement value for the bars (RMS or peak).
- Peak Hold Time – defines the time for which the hold markers should be held after an update (higher or equal value).
- Infinite Hold Marker – activates an additional marker that remains at the highest peak value. The reset is done manually with Infinite Hold Reset or double click.
- Infinite Hold Reset – resets the permanent hold.
- FSC Count for OVR – specifies the number of full scale samples that must have occurred in succession before the peak display shows "OVR". The hexadecimal value 0x7FFF00 counts as full scale, so that 16-bit signals can also trigger an OVR
- Intersample Peak (TP) – activates an oversampling filter which calculates further points in the signal curve between received samples. With compressed music, these samples can go beyond the digital "full scale" (imaginable as an outwardly curved connecting line between 2 full-scale samples) and thus leading to overloads in downstream devices (D/A converter, sample rate converter, etc.). This function, also often referred to as "True Peak", increases the display range of the peak meter. For reference levels above -10dB, the display range is therefore extended upwards by 3dB. The OVR determination using full-scale samples is switched off. Instead, the peak markers above 0dB full scale are displayed in white.
- RMS + 3dB – enables the alignment of the display values ​​of RMS and peak. Mathematically, the RMS for a sinusoidal signal is 3dB lower than the peak value due to the quadratic mean value calculation, which leads to a poorer readability of the meters without this option.
- RMS Slow Marker – activates a marker based on an RMS calculation with a very long time constant. This enables the reading of weakly variable values ​​with high accuracy (also as numerical value in text level) or the estimation of the energy (volume) of dynamic signals.
- RMS RLB Filter – the RLB filter is a weighting filter from the context of loudness measurement (ITU BS.1770) and enables an improved mapping of loudness in RMS measurements. It significantly attenuates the signals in the bass range. The option only affects the RMS value.
- K-System – configures the level meters according to the specifications of the legendary mastering engineer Bob Katz. The setting is selected by the reference value (headroom) and affects various parameters for scaling, color switching, true peak, etc., which can no longer be set manually when the K-System is activated. Their previous settings are saved in the background.
- Show Pair Difference - enables indicators of level difference between 2 channels. The difference between the RMS or RMS Slow values is shown, not the level of the differential signal (which can be different due to phase effects). The indicators can be used to monitor the balance of stereo channels.
- Diff. Indicator Range – sets indicator display range.

Setting parameters R 128 Meter

- Predefined Scale – allows the selection of the two scales recommended by the EBU with 9dB and 18dB top level. The reference (0LU) is set to -23LUFS. The selection "OFF" switches to the settings of the normal level meters of the respective instrument, including Reference Level.
- Momentary Marker – switches on a peak hold marker for the momentary display, optionally with an infinite hold time (reset by double click).
- Short Term Marker – configures a marker in the short term display, either peak hold or slow for additional integration of the display value.
- Show M&S Bars only – switches off the integrated value bar and the text field so that only momentary and short term values are displayed.

### Bitstatistics and Noise

The bitstatistics shows for each bit of the audio data whether it changes (green '*' symbol) or remains at a fixed value (0 or 1). The bits are converted from the 32-bit float data provided by CoreAudio. These have 23 bit mantissa and a sign bit, so that in the range -1.0f to + 1.0f 24 bits can be represented exactly as an integer, which corresponds to the resolution of most current audio and digital interfaces.

Of course, digital signals can also have a smaller bit width; the lower, unused bits then remain at zero. If bits are fixed at 1, this is usually a sign of an failure in audio signals. Only with special test signals with high frequencies synchronized to the sample rate can individual bits remain at 1. Fixed bit patterns are also established when transmitting DC signals. A mixture of audio signal and DC (as an offset, e.g. with A / D converters without digital high-pass filter) shows the DC value in the higher bits in the idle state, the lower bits change due to the inherent noise. As the input signal increases, more and more bits change.

In the following columns, the level of the input signal is displayed as RMS (Root Mean Square), once with a limitation to the audio band from approx. 10 Hz to 20 kHz (marked as "LB" for limited bandwidth) and once weighted with the weighting filter type A (marked as dBA). The type A weighting filter simulates the sensitivity of human hearing and is the standard for measuring signal-to-noise ratios, in digital systems mostly based on digital full-scale.

The last column shows the DC component of the input signal. For this purpose, a steep-edged low-pass (since version 0.90 with 2 stages) followed by slow integration is used. The display is in dB related to digital full scale (2 ^ 23 - 1), a '+' or '-' shows the polarity. At very low frequencies the filter cannot extract a DC signal and the display values fluctuate.

Setting parameters

- Channel Count - defines the number of channels available on the instrument
- Show Channel Names - switches to the display of the (shortened) channel names of the audio interface. Otherwise the channel numbers are displayed.
- Integration Time - sets the filter effect for the RMS and DC measurements. The "auto" setting follows changes very quickly and switches to slower time constants when constant values are observed. In most cases this setting will be optimal. A manual selection can be advantageous for the evaluation of strongly changing input signals: If the display should follow quickly, "fast" is recommended, if the level should be strongly integrated (filtered), "medium" or "slow" fits.

### Frequency Measurement

The frequency measurement function determines the frequencies in an audio signal. In the case of sinusoidal tones, this is directly their frequency. In the case of mixed frequencies, if the frequencies can be separated, the signal component with the largest amplitude is evaluated, a search for the basic frequency is carried out, or several frequencies are determined, depending on the selected strategy. The window of the function shows a spectral display in which the evaluated frequency ranges are marked lighter.

Frequency measurements with non-pure sine tones are inherently subject to many uncertainties, the results should always be checked carefully for plausibility.

Setting parameters

- Channel Select – allows the input channel to be selected from a pair of channels or their sum.
- Strategy - specifies how the evaluation is carried out. "Maximum Level" searches for the frequency components with the highest level. With "Suppress K2 & K3" the fundamental is determined if K2 and K3 are not more than 10dB above the fundamental. "Multi Frequency" displays several detected frequencies in ascending order. The level of the respective signal must not be more than 25dB below the maximum value.

### Oscilloscope

This instrument emulates a simple DSO with up to 8 channels. The X-axis (horizontal) has a time-related resolution, the scaling values of the Y-axis (vertical) refer to 1.000 for full scale.

The signal memory contains 2048 points, of which approximately 50% are displayed depending on horizontal scaling. At high time resolutions, optional oversampling ensures an analog-like representation of the areas between the samples. At low resolutions, an average filter allows the samples to be summarized. If this filter is not switched on, only 1 sample is used at the respective sampling point.

The window of the instrument has a control panel that can be made smaller or switched off completely. All permanently effective settings are also accessible via the Settings window. The horizontal position of the trigger and its value on the Y-axis can be adjusted directly with the mouse.

The size of the control panel scales with the appearance setting "Text Size Labels".

Setting parameters

- Show Control Panel – controls the visibility of the control panel. In the panel itself you can only switch between "Small" and "Full" (triangle at the top left).
- Activation and deactivation of individual channels – is only available in the control panel (top line). Basically, the channels are selected in the input settings. When the function is started, all assigned channels are activated. The switches described here are only used to quickly adjust the display when working with the instrument.
- Vertical Scale – scaling of the samples in the vertical direction. Value in divisions based on 1.0 for full scale.
- Vert. Position Ch. x – position of the channel's curve in the vertical direction, adjustable in whole divisions. In the control panel, the available values are stepped through when you click in the field.
- Horizontal Scale – Scaling of the display in the horizontal direction. Specified in time per division.
- Trigger Position – Location of the trigger point in the horizontal direction. Specification in divisions. The recording lengths before and after the trigger are adapted to this setting. When the recording is stopped, the display can be moved, also with the mouse in the window.
- Trigger Level – Value that the trigger channel must exceed/undershot to trigger the trigger event. Here too, the reference is 1.0 for full scale. There is a reset button on the control panel for setting the value to zero. The position and thus the value can be changed directly with the mouse depending on the set vertical scaling.
- Trigger Channel – selects the channel that is monitored for the trigger condition.
- Trigger Slope – Direction of signal change for a trigger event.
- Trigger Mode – DSO operating mode. In "Auto" mode, a recording is triggered automatically after a short time without a trigger event. "Normal" means that only valid trigger events lead to an update of the display. If "Fade" is also activated, the last recording will be faded with the time constant set for "Afterglow". This makes it easy to see how far ago a trigger event occurred. Without "Fade" the last curve remains. The same in “Single” mode, with which only 1 trigger event is recorded and displayed at a time. All modes can also be switched off using the buttons on the panel. Then the state of the memory is retained (corresponds to deactivated "Trigger Enabled" in Settings).
- Trigger Enabled – activates recording upon a valid trigger event. If not active, the state of the memory is maintained. Settings for display control (scaling, positions) can still be changed and thus the display can be adapted.
- Fade (last recording) – activates the fading of the last recorded curve in trigger mode “Normal”.
- Trigger button – button (only present in the control panel) which lights up when a trigger event occured, can trigger a recording manually at any time when pressed.
- Filter/Oversampling – controls the handling of samples that cannot be displayed due to the time scaling of the horizontal axis (filter) or are missing at high resolutions (oversampling). The filter for downsampling is an average filter; for oversampling, 2 or 4 times oversampling is used. Due to its transient response, this filter distorts the signal curve for invalid signals (e.g. square wave signals or hard switching on of audio signals).
- Live Update – controls whether an update of the display should take place during recording from a valid trigger event or only after completed recording. This is particularly useful for long recording times (large values for horizontal scaling), where faster readability is achieved. That's why the option "100 to 20ms/div" is chosen as default setting.
- Afterglow Time – controls the afterglow of the curves in the display. Without "Fade", the last recorded curve is displayed permanently; the fading then only applies to previous recordings.

### Spectroscope

The Spectroscope analyzes the frequency components of a signal using FFT and displays them as color over a time axis.

Typical for FFTs is a linear distribution of frequencies for which the signal strength is determined. The larger the FFT, i.e., the longer the measurement window, the higher the frequency resolution. A large length would actually be needed for good resolution at low frequencies, but this leads to very poor temporal resolution. Reassignment helps counteract this by extracting additional information from continuously executed FFTs and thus sharpening the FFT. Our instrument uses the algorithm by Patrick Flandrin, François Auger, and Eric Chassande-Mottin (paper "Time-Frequency Reassignment: From Principles to Algorithms" 2017), with modifications for continuous measurement and high graphic resolution. This algorithm is magical, but it can't completely cure all problems: If a very small FFT size is set, the display begins to degrade somewhat. For synthetic low-frequency signals (where the sharpening is strongest), artifacts may become visible. Ultimately, the setting depends on the application and requires some trial. Reassignment also introduces some latency into the display, depending on the FFT size.

You can choose between a scrolling display and a stationary display (with moving writing position). Entering new data can be paused using the pause button at the bottom of the instrument.

Clicking into the spectroscope graphic displays a horizontal cursor with the corresponding frequency. This cursor can optionally snap to the nearest note. Moving the mouse while holding down the left mouse button overlays the function for swapping instruments between the fields. If the mouse is moved only slightly after holding down the left mouse button, only the cursor function remains active.

The implementation is designed for audio signals. For sample rates above 48 kHz, downsampling is used to keep the CPU load constant. For signals above 20 kHz with very high levels, this can lead to slight mirroring effects.

If the CPU load exceeds the available performance (e.g., at high Display Speed and larger FFT), the calculation can no longer follow the audio signal. The missing areas are then displayed in white. CPU load is signal-dependent when reassignment is active.

Setting parameters

- Channel Select – controls the use of the input channels. In addition to Left and Right, Sum and Difference can be selected.
- Enable Reassignment – enables the above-mentioned sharpening algorithm. When disabled, the normal FFT is displayed, which is intended for comparison purposes only.
- FFT Size – FFT size. A smaller value results in higher time resolution with lower frequency resolution. This also affects the CPU load, which increases with larger values. 4096 is usually a good value.
- Reference Level – specifies the level for maximum brightness. This parameter allows the adjustment to the highest sine wave components in the signal, even with the Settings dialog closed, using the buttons on the display. Overloading at higher levels does not occur; only color differentiation is no longer possible.
- Display Range – specifies the dynamic range to be displayed (relative to digital full scale). The conversion is performed as the brightness of the color linearly to the logarithm of the level (can be changed nonlinearly using Compress/Expand).
- Compress/Expand – allows the color curve to be bent. A negative value lowers the middle range with a second-order line; a positive value raises it. This acts like a compression or expansion of the resulting color.
- Color – specifies the color of the frequency display. At high levels, a transition to white occurs.
- Display Speed – specifies the horizontal resolution at which new FFTs will roll into the screen. The numerical values ​​are only approximate, and the optical speed is influenced by the monitor resolution. A higher speed leads to a higher CPU load.
- Frequency Range – Display range in the Y direction (frequency).
- Show Grid – enables orientation lines in the X and Y directions.
- Reassign Range – affects latency and resolution. The above-mentioned reassignment algorithm theoretically affects FFT results that are far in the past or far in the future. This is rather unfavorable for real-time implementation (very high latency). The "standard" setting covers the normally expected range. "short" halves the latency.
- Stationary Display – switches from scrolling the entire display to moving only the writing position.
- Hide Control Panel – turns off the controls on the display.
- Show Color Scale – displays the resulting color scale for a level range of 0 to -120 dB full scale on the right.
- Show Note Cursor – snaps the frequency cursor (left mouse button) to the nearest note, reference as specified in the option.

### Credits

FFT uses rdft(): Copyright(C) 1997,2001 Takuya OOURA (email: ooura@kurims.kyoto-u.ac.jp).

Reassignment is based on mathematical concepts from Patrick Flandrin, François Auger, Eric Chassande-Mottin. Time-Frequency reassignment: from principles to algorithms. Antonia Papandreou-Suppappola. Applications in Time-Frequency Signal Processing , 10, CRC Press, pp.179-204, 2002, Electrical Engineering & Applied Signal Processing Series, 9781420042467. hal-00414583

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