[sdiy] Mixed-signal problems (dsPIC digital delay project)

P Maddox yo at vacoloco.net
Thu Jan 26 20:04:34 CET 2017

As someone said, you shouldn't hear 64K and 2.7M. 
Have you got a picture of the scope with a sinewave coming out the DAC?
  Original Message  
From: Tom Wiltshire
Sent: Thursday, 26 January 2017 18:59
To: Richie Burnett
Cc: synth-diy at synth-diy.org
Subject: Re: [sdiy] Mixed-signal problems (dsPIC digital delay project)

On 26 Jan 2017, at 17:13, Richie Burnett <rburnett at richieburnett.co.uk> wrote:

> "The spikes are causing an oscillation at around 2.7MHz. This comes out as basic white noise on the audio."
> What makes you think that the 64kHz pulses or 2.7MHz ringing are causing white noise at the audio output? You can't hear 64khz or 2.7MHz after all?

If you look at the output on the 'scope, you can see a pile of background fuzziness - noise. If you zoom in, you find that it has some structure in the apparent noisy background. Firstly, it comes in little bursts at 64KHz. Secondly, if you zoom in even more, the little bursts look like a high-res "ping" at about 2.7MHz.

If those things weren't there on the output, the output would be clean (the bits in-between spikes look pretty good!). Given that it isn't, isn't it logical to assume that the noise I can see and the noise I can hear are the same?


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