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Pulse Width Units - Percent / Degrees / Samples / Seconds

Controls: Gen Dlg >> Stream >> Wave >> Pulse >> Units
Macro: PulseUnits

This set of radio buttons selects among Percent, Degrees, Samples, or Seconds as the units for entry and display of the two Pulse Width values. You may choose whichever units are most relevant for your application, keeping in mind the interaction with main wave frequency and the effects upon modulation options, described below.

Percent and Degrees are relative units, so the actual pulse duration will vary with frequency. If you set the frequency too high, pulse widths may be reduced to less than one sample and you will get unpredictable results.

Samples and Seconds are absolute units, so only the baseline (0 Level) duration changes with frequency. If you set the frequency too high, the baseline dwell time may be reduced to less than one sample and you will get unpredictable results.

With Percent or Degrees selected here, the Phase Modulation (PM) option in the main Stream dialog changes to PWM to allow Pulse Width Modulation. That's indicated here as a reminder, via '(PWM)' next to these buttons.

With Samples or Seconds selected, the modulation option is Phase Modulation and the reminder is '(PM)'.

Pulse Width Modulation (PWM) is commonly used in many areas. The output signal can be purely digital, on or off, but the average value changes with the modulation. The digital nature makes it easy to send the signal over a simple interface (such as an optoisolator), yet it is easy to recover the modulating signal via a simple low-pass filter.

PWM is the traditional method used in high-efficiency Class D amplifiers. Each output device (transistor) is always in either the full-on or full-off state, neither of which dissipates much power in the device itself, delivering it instead to the load. For audio amplifiers, the basic pulse frequency must be high enough so that it is out of the range of human hearing (well above 20 kHz). A simple low-pass filter at the output is typically made from an inductor and a capacitor.

Macro Notes:

R.2.PulseUnits=Pct sets Right Stream 2 Pulse Units to Percent, or use Deg, Smpls, or sec instead. You can use Channel Select variable Ch to specify the channel and stream via Ch.PulseUnits=Pct, where Ch has previously been set to 0-3 (for L.0. to L.3.) or 4-7 (for R.0. to R.3).

Alternatively, you can use numeric values, variables, or expressions in place of names like 'Pct':

    0 = Pct
    1 = Deg
    2 = Smpls
    3 = sec

Separate Units settings are maintained for each stream.

Note that setting Pulse Units directly via macro does not automatically set the Wave to Pulse. Use Wave=Pulse to do that.

See also Wave Dialog, Pulse Wave.


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