Data Zero - Average (Zero Av)

Controls: Zero Dialog >> Average
Macro: ZeroData=Avg

Data Zero Average (shortened to Zero Av on the toolbar button) determines the DC value of the waveform by averaging all 1024 trace samples together. It then subtracts this value from each sample of the waveform. This is an ongoing process, repeated on every display update as long as Data Zero Average is set.

Data Zero Average removes the constant (DC) value from a waveform to capture only the varying (AC) portion. (The following Peak option performs a similar function.)

Unlike Screen Zero, Data Zero modes do affect the cursor readouts, Trigger operation, and file output. For normal waveforms and for Linear or Exponential Waveform Averages you can change the settings after the data is captured, but Histogram and PSTH averages can't be modified after the fact.

This option shouldn't be needed for most sound card inputs, since they are AC-coupled by design. However, some cards are better at this than others. Due to a leaky coupling capacitor or similar problem, a small offset voltage may be present. This can be a particular problem on Mic inputs, which have a high gain stage between the input and the ADC. The data zero may thus be many millivolts above or below the true zero.

For most waveform operations this type of error merely shifts the trace up or down, which can otherwise be corrected with a simple Screen Zero setting. But it may be a particular problem for Histogram and PSTH averages, since it actually changes the distribution of values.

When Data Zero Average is active, the main toolbar Zero button changes to 'Zero Av'. Please note that the toolbar button state pertains to the Screen Zero option, but the button label indicates whether any Data Zero state is active, regardless of the toolbar button in/out state.

Macro Notes:

ZeroData=Avg or ZeroData=1 sets Data Zero Average mode. The numeric value can be supplied by a variable or expression.

ZeroData=0 cancels all Data Zero modes.

Note that attempts to use the ZeroData command when it is disabled in Spectrum, Spectrogram, or Pitch Track modes will result in "Control disabled. Aborting macro." You can check if this control is enabled via an E.IF.ZeroData= control enable IF test.

See also Zero (Screen and Data)