Decimate On/Off

Controls: X-Axis Dialog >> Slow >> Decimate
Macro: Decimate

When the Decimate button is active, the effective display sample rate is reduced by an arbitrary Decimation Factor, without changing the actual sample rate used by the Generator.

The actual rate can thus remain high (such as 48000 Hz or more) to allow optimum high-frequency detail in generated signals, while the display shows a condensed waveform that covers a long time span, such as might otherwise be seen with a slower sample rate... but which would cause aliasing of the output signal.

Even if you are not generating signals, Decimation can be very useful for monitoring low-frequency (or even DC) inputs, or higher-frequency events that happen infrequently. In addition to offering arbitrarily low effective sample rates (much lower and more accurate than Windows or the sound card can supply), Decimation allows the Envelope option to capture maximum and minimum information which would otherwise be lost by actual sample rate reduction.

At very slow effective rates (anything below about 500 Hz or so), it is usually best to run with Trigger off. This will result in a scrolling waveform that emulates a conventional chart recorder or data logger.

With Trigger on, the display only updates when a trigger event happens. At slow rates, and especially with infrequent trigger events, this may make the display appear to stall.

Note that in normal Decimate mode (and in Decimate Envelope mode), the trigger operation is by default applied to the raw data, not to the decimated data. The Trigger Source label becomes a button marked 'Source Raw', which can be toggled to 'Source Decimate'.

Since the decimation process acts like a low-pass filter, Source Decimate can be used to remove noise and high-frequency signals that affect triggering but are not seen in the decimated display. Conversely, Source Raw allows you to trigger on a transient that may be eliminated by the filtering action, such when viewing a slow or delayed response to a narrow pulse.

See also Slow (Decimate) Controls, X-Axis Control Dialog