Data AcQuisition And Real-Time Analysis
Scope - Spectrum - Spectrogram - Signal Generator
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Spectrum Track Threshold

Controls: Spectrum Dialog >> Track >> Threshold
Macro: TrackThresh
Changes: RT=n

This control allows you to limit the Track action to peaks above the threshold level you specify, to prevent spurious tracking of noise peaks when the desired signal is absent.

The threshold is a single value, which is expressed according to the current Y-axis mode in volts, dB (if Y-log is active), or User Units.

To the left of the control is a small box which shows the Spectrogram color corresponding to the threshold value. If you are setting the threshold for use with the Spectrogram Pitch Track option, it is usually much easier to adjust from the Spectrum display instead of the Spectrogram or Pitch Track display.

Note that this threshold color is a function of the Spectrogram range and Color Palette as well as the Track Threshold setting.

Note that this control value is saved to and loaded from MIDI Setup (.DQM) files. Loading a new MIDI Setup may change its value.

Macro Notes:

Important: The TrackThresh macro assumes the units of the current Y-axis mode. If Y-log is active, the units are expected to be in dB relative to full scale. If User Units is also active, the units might be in dB SPL, which will give very different values.

For example, TrackThresh=60 will set 60 dB SPL if Y-log and User Units are active (assuming the units are Pa and the SPL button is active in the User Line dialog). But if User Units is off, this same command will set -60 dB since 0 dB is full-scale so a minus sign is always assumed.

If Y-log is off and User Units is on, the same command will attempt to set 60 Pa (or 60 of whatever units are active). If both Y-log and User Units are off, it will attempt to set 60 volts.

Due to these issues, it would be wise to precede a TrackThresh macro with macros to insure that the expected modes are active.

You can also increment and decrement the threshold via macro. TrackThresh=>1 will increment by 1 dB in any dB mode. In linear modes the step size is that used by the little up/down arrows on the control itself, which is 1/32768 of the full-scale range. TrackThresh=>-1 will decrement by the same amount. Only single-step increments and decrements are allowed.

MIDI Changes Script:

Use RT=n to set the Spectrum (Pitch) Track Threshold to n dB, where n can be any integer or valid Changes script expression. This may consist of MIDI control values (including RT), random values, current computer keyboard states or mouse position, input or buffered notes, oscillators, or User Variables.

Note that unlike the TrackThresh macro, this Changes script command always uses dB and ignores User Units. This allows it to operate consistently regardless of current system settings.

When setting the threshold, the given dB value is always presumed to be negative (or zero), regardless of actual sign. When reading the threshold (RT on the right side of the expression), the returned value is always negative (or zero). For example, RT=RT+1 will increment a negative threshold up toward zero. If you give this repeatedly the threshold will eventually reach zero, but on the next pass the right side will evaluate to 0 + 1 = +1, which will be assumed to be negative and so the threshold will go back down to -1 dB. On the following pass it will increment up to zero, in an endless cycle.

See also Spectrum Cursor Track Dialog, Spectrum Control Dialog, Spectrogram / Pitch Track Controls


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