[alsa-devel] Distorted jackd output on Macbooks

Adrian Knoth adi at drcomp.erfurt.thur.de
Tue May 8 16:45:30 CEST 2012

On Tue, May 08, 2012 at 01:01:32PM +0200, Takashi Iwai wrote:

> > JFTR, we've seen users that report distorted sound on their macbooks
> > when using jackd.
> > 
> > The workaround is to force 16-bit output:
> > 
> >     http://jackaudio.org/macbook_distortion
> > 
> > Chip in question was the Cirrus Logic CS4206. We don't know yet which of
> > the formats (32/24) is broken, maybe only one, maybe both.
> Distrotion means noisy outputs or complete noise?

Noisy output, like clipping. As if the MSB would be wrong.

Here's an example:


> And does this happen only with JACK?  That is, if you run "aplay -Dhw"
> with 32bit PCM, does it play normally?

I've installed Linux on my spare MacBookPro and can report that JACKD is
not to blame. aplay and jackd behave the same:

   FLOAT_LE is distorted
   S32LE is fine

So only FLOAT_LE is broken, S32LE and S24_3LE are fine.


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