Question - scratchy audio

Question - scratchy audio

[David McNab]

Hi,

Having (at the moment) failed to get the ALSA realtime/abs queueing 
working, I've resorted to having my app spit out direct events, and 
things are working reasonably well.

However, I've got a problem, where I'm getting intermittent 
'scratch'/'pop' noises (sounds a bit like a dodgy jack or lead).

Any ideas what could be causing this?

-- 

Kind regards
David



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Re: Question - scratchy audio

[David McNab]

David McNab wrote:
> However, I've got a problem, where I'm getting intermittent 
> 'scratch'/'pop' noises (sounds a bit like a dodgy jack or lead).
> 
> Any ideas what could be causing this?

For the benefit of others who may be new to alsa seq api, I'll post what 
I found out.

It seems that if a client process is spiking the CPU, even for short 
bursts, it will impact one or more other audio progs. Not sure whether 
the scratchiness is caused by ALSA, fluidsynth, or something else 
getting momentarily cpu-starved.

Solution - I optimised my (python) client app, psyco'ed the scheduler 
loop, and shimmed to C functions which create and dispatch the events.

It turned out that my python code was doing a lot of unnecessary object 
creation and dict manipulation, which was causing CPU spikes. Seems that 
even a spike of a couple of ms can impact the audio.

Result - instead of scratchy audio, with jerky off-time notes sounding 
like a garage band with a 3-day hangover, the music is now coming 
through clear and rhythmically tight.

Seems I won't need to bother battling with alsa queues and scheduling 
any more :))

Cheers
David



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