Daqarta
Data AcQuisition And Real-Time Analysis
Scope - Spectrum - Spectrogram - Signal Generator
Software for Windows
Science with your Sound Card!
The following is from the Daqarta Help system:

Features:

Oscilloscope

Spectrum Analyzer

8-Channel
Signal Generator

(Absolutely FREE!)

Spectrogram

Pitch Tracker

Pitch-to-MIDI

DaqMusiq Generator
(Free Music... Forever!)

Engine Simulator

LCR Meter

Remote Operation

DC Measurements

True RMS Voltmeter

Sound Level Meter

Frequency Counter
    Period
    Event
    Spectral Event

    Temperature
    Pressure
    MHz Frequencies

Data Logger

Waveform Averager

Histogram

Post-Stimulus Time
Histogram (PSTH)

THD Meter

IMD Meter

Precision Phase Meter

Pulse Meter

Macro System

Multi-Trace Arrays

Trigger Controls

Auto-Calibration

Spectral Peak Track

Spectrum Limit Testing

Direct-to-Disk Recording

Accessibility

Applications:

Frequency response

Distortion measurement

Speech and music

Microphone calibration

Loudspeaker test

Auditory phenomena

Musical instrument tuning

Animal sound

Evoked potentials

Rotating machinery

Automotive

Product test

Contact us about
your application!

Slow Timing Mode

Controls: Gen Dlg >> Stream >> Smooth TC >> Slow
Macro: TmMode=Slow

Timing mode is set via the three-button control at the top of the Random / Step Timing Dialog.

Slow mode uses the Slow Factor control to slow the wave by the indicated amount. This is accomplished by interpolating extra samples between the original samples; it does not change the sample rate, only the "speed" of the signal. For noise waves, this allows very slowly changing outputs while still keeping a large signal level. This is particularly valuable where you want to use the output as a modulator for some other process.

Contrast this with simple low-pass filtering, which would result in a proportionally smaller level as the bandwidth was reduced. While the average output level would be smaller, the maximum possible output level would not be affected... it would simply be less probable. This is because the random sources have occasional runs of the same value, as any true random source should. So, if you filtered the noise to a low average level and then boosted the output, there would be occasional high-level runs that exceeded the output range. When that happened the output would be limited to its full-scale value, and the suppposedly low-frequency output would have high-frequency content due to the clipping.

But in Slow mode the output level is not affected as you make the signal slower. However, due to the linear interpolation, the output is not equivalent to a large low-pass filtered version of the raw waveform. Each of the original data points is present, but spread out in time by the Slow factor and simply connected by straight lines.

If this is not suitable for your purposes, use the Smooth function. Set the Smooth TC to about the same value (in samples, not time) as the Slow factor and you will have a fairly decent approximation to a "big, slow" version of the source. The level will be reduced slightly, but much less than the comparable reduction from filtering. The Smooth function is indeed a simple low-pass filter, but here you only need a relatively mild filtering action to remove the straight-line distortions, not to provide the entire low-pass action.

For comparison, you may want to try setting the Slow factor to 1x and attempting to do all the low-pass filtering with the Smooth control. Or you may want to try using the Noise Band source with the frequency range set very low.


Macro Notes:

L.1.TmMode=Slow or L.1.TmMode=1 sets the Left Stream 1 Timing Mode to Slow.


See also Spec Timing Mode, Step Timing Mode, Random / Step Timing Dialog.


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