Re: [LAU] [SOLVED] Example captured: Crackles in audio, drifting intermittent noise etc.

On Tue, 01 Nov 2016 00:24:16 -0400
termtech <termtech@email-addr-hidden> wrote:

> Yeah nice one but I doubt heat related - more like voltage drop spike
> related, more activity on the power rails causing more spikes causing
> the audio card to glitch.
>
> In the original thread we talked about weak capacitors on the sound card.
>
> I was seriously contemplating that possibility once again today,
> until I managed to capture the sound and analyze it :
>
> https://dl.dropboxusercontent.com/u/53315356/Test_tone_passthru_noise.ogg
>
> It is a recording of a hardware audio sine generator (my keyboard),
> input to the Delta1010, recorded as it is being passed through to an
> audio output via Jack. What you hear is what I hear out of that output.
>
> Hey all you digital audio experts!
> Listen to the recording, be patient and watch how the distortion slowly
> drifts in then out. Open it in Audacity or something, and notice the spikes.
>
> Seems to me, that you can tell by the distortion's overtones which slowly
> rise in spectrum then disappear, that this /resembles/ a textbook case of
> some read pointer 'meeting up with' and passing some write pointer and
> when they meet there is distortion.
> In other words they are at slightly different /rates/.
>
> Do you hear what I mean about being easily recognizable as a sync problem?
>
> But how? And why core related?
> I mean... I'll have to check chip docs but the card may have separate
> read and write sample rates...
> But no, look closely at the spikes in the wave in Audacity. It appears some
> buffer is 'starting' too early or too late - like the buffer is suddenly
> being switched in the middle of a wave and it is that switching time
> that is varying.
>
> So maybe not a /soundcard/ clock rate problem but something is not filling
> the buffers at the right time? Again - core synchronization?
>
> Also, aside from the drifting noise, notice the slight glitches in the sound
> that are pervasive throughout.
> /That/ is what I hear even with simple playback of test tones on websites!
> You can hear the clock rates jumping around slightly. Yes, I know this is
> /usually/ caused by Speed Step, Hyper Threading and so on, but the
> fscking thing does it with all such setting turned off. On the other PC too.
>
> Only choosing TWO (or one) cores instead of FOUR stops all these noises.
>
> Thanks for listening. Whaddya think?
> Tim.

As a matter of interest, have you got access to a USB sound unit? If so does
that exhibit the same problem?

The reason I ask is that I have a Novatech nspire laptop with a quad core i5,
and have no issues at all using it with a KA 6 - indeed I used it on last
year's LAC where it was running for an hour and a half. At that time it wasn't
even running an RT kernel.

-- 
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
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