[pulseaudio-discuss] PulseAudio sample type conversion and quality

Lennart Poettering lennart at poettering.net
Wed Mar 31 03:39:43 PDT 2010

On Wed, 31.03.10 12:10, Oscar Eriksson (oscar.r.eriksson at gmail.com) wrote:

> Hi,
> I'm curious about how the conversion from 32-bit float PCM to 16-bit fixed
> PCM is done in PulseAudio. Or is it Alsa that takes care of this
> conversion?

PA does.

> Are noise shaping and dithering involved?

No and no. I thought about adding at least dithering, but uh, I don't
think this is really a priority for desktop audio. Dithering is primarily
relevant for audio production which PA is unsuitable for anyway, and
the operation is too CPU intensive to do it nonetheless.

(ALSA doesn't do thopse things either in their converters)

> Also, how do I adjust the volume for optimum playback quality when playing
> music? (I want to use the the full dynamic range) Should I use maximum ALSA
> and PulseAudio volume when playing songs that have been normalized (Replay
> Gain)?

For the sliders PA exposes 0dB is at maximum hardware volume, and the
"base volume" is where the hardware 0dB is, for whatever that means.

Hence normally you want to keep the volume below the base volume, at
least when the dB labelling of the hardware sliders are correct.



Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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