[pulseaudio-discuss] Monitoring and Pulseaudio accuracy

Tanu Kaskinen tanuk at iki.fi
Mon Nov 30 08:54:38 PST 2009

ma, 2009-11-30 kello 10:33 +0000, Neil Wilson kirjoitti:
> Hi all,
> I have pulseaudio running on Ubuntu and send the sound digitally to a
> set of High end digital speakers. Since it is Hi-Fi, the work I'm
> doing involves ensuring wherever possible that the digital bits are
> not disturbed by the software systems the value is passing through -
> unless it has to be when the softphone rings.
> I did a simple test using pacat and parecord on the sink Monitor with
> a set of float32le tones representing a simple log sweep through the
> frequency range. Volumes were set to 100% across the entire chain. Yet
> when I checked the float values, they had been perturbed by a small
> amount.
> That got me thinking. Can pulseaudio maintain a 'clean path'
> throughout the entire software chain?

Are you sure your files had the same sample format as what your sound
card uses? If pulseaudio doesn't need to do mixing or resampling or
sample format conversion, I'm surprised if the bytes are touched.

So, you had float32le tones. Is your sink also configured with that
format (see "pacmd list-sinks")? Do the sample rates match between the
files and the sink?

Tanu Kaskinen

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