Re: PCM vs PWM for low distortion sinewaves

On Jan 30, 8:41 am, Vladimir Vassilevsky <antispam_bo...@xxxxxxxxxxx>
wrote:
BobW wrote:
I'm attempting to generate low distortion sinusoids (in the 200Hz - 3KHz
range). There will be a fixed number of amplitude changes for each period
regardless of the frequency being generated.

If the sample rate is the exact multiple of the frequency of the
sinewave, then all of the distortion will be concentrated at the
harmonics of the sinewave. This is not good.

If we keep the number of pulse width or amplitude changes per period the
same (let's say 32 per period), and the resolution the same (16 bit DAC or
16 bit pulse width resolution), and the final filtering is the same (2 pole)
and constant (i.e., not tracking) -- do you think that I can get lower
distortion using 16 bit PCM or 16 bit PWM?

So, you have the 2nd order LPF with Fc at ~3kHz, hence the THD is going
to be as bad as 20% or so at 200 Hz at the best.

The PCM will generate less artifacts then PWM. For the PWM, you will
have to predistort the sinewave, and it will be a lot of trash above
Nyquist.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultanthttp://www.abvolt.com

Good points here. I suspect the original poster is going to do a
simple table look-up, hence the sample rate being a multiple of the
sine wave to keep the look-up table smaller. If a coordic was used,
the sample rate could be a non-multiple of the sine wave.

.

Relevant Pages

  • Re: PWM -> Audio Output
    ... The audio output works but the quality is not quite there. ... from my device which do not appear in the RAW file.... ... I've discovered that I can remove these artifacts by changing the PWM ... have set to be a multiple of the sample rate. ...
    (comp.arch.embedded)
  • Re: PWM -> Audio Output
    ... The audio output works but the quality is not quite there. ... from my device which do not appear in the RAW file.... ... I've discovered that I can remove these artifacts by changing the PWM ... have set to be a multiple of the sample rate. ...
    (comp.arch.embedded)
  • Re: PCM vs PWM for low distortion sinewaves
    ... If the sample rate is the exact multiple of the frequency of the sinewave, ... lower distortion using 16 bit PCM or 16 bit PWM? ... The PCM will generate less artifacts then PWM. ... Another alternative is to have a tracking filter (a switched capacitor ...
    (sci.electronics.design)
  • Re: Is higher oversampling ratio better in signal fidelity in digital world?
    ... as you lower the sample rate you increase the ... digitization (Your sampled sine wave will start to look like a square wave). ... Clocking that data through a DAC at the same rate will produce strong ...
    (comp.dsp)
  • Re: Question: Learning How To Use Hand Held Oscilloscope
    ... What the plot looks like is this: consider a repeating sine wave. ... frequency on the function generator these repeating waves become more ... and what is the sample rate of the scope? ...
    (sci.electronics.basics)