[pulseaudio-discuss] pulseaudio settop boxes

[Laurențiu Nicola]

Hi Wolfgang,

First of all, I hope I won't offend anyone with this email, as it's not
really related to PulseAudio and I should probably have taken it
off-list.

The complaints are usually related to the integrated sound card, which
uses PWM (although at a rather high frequency). I tried to use it only
once and, while I can't really comment on the audio quality, it seemed
to have a lot of interference: when the Pi was writing to the SD card,
there was a lot of audible noise. I'm using an USB DAC (sound card).

Initially I was using ALSA, but the audio was choppy until I changed the
sampling rate to 44100 Hz. The USB support is not great on the Raspberry
Pi and there was a series of kernel changes intended to fix some
problems with keyboards or something like this. I'm running mine
headless, and those changes caused audio distortion for me, but luckily
they can be disabled from configuration. The Raspberry Pi also has I2S
support, which is a dedicated audio bus, supporting high sampling rates
and bit depths. There are some I2S sound cards available and the drivers
were recently merged into the kernel.

Another series of problems was SD card corruption for me, as the Pi
would not boot anymore if I restarted it improperly (which happens quite
often because the power connector on mine is a bit finicky), but this
seems to happen less often with newer firmwares.

As for PulseAudio, I'm using the RTP module with an application I wrote.
The CPU usage is rather high, but this is probably due to the resampler
(which is needed for RTP because of the clock skew). The rate estimation
algorithm seems to be a bit buggy: sometimes the buffer size grows too
much, at other times the audio gets choppy (although I find it weird
that I have to restart PA, not just the RTP session to fix it) and
sometimes it stops playing at all. However, I expect that these are
issues with the RTP module, not with the rest of PulseAudio.

Basically, you can make it work and it's not that much of a hassle.

Regards,
Laurentiu

On Sat, Feb 8, 2014, at 23:00, hamann.w at t-online.de wrote:
> >> Hello,
> >> 
> >> I'm not sure this is what you expect to get as an answer, but I'm using
> >> PulseAudio on a Raspberry Pi. It "mostly" works.
> >> 
> >> Laurentiu
> >> 
> 
> Hi Laurentiu,
> 
> I thought about something along these lines ... but I recall that people
> are complaining
> about the audio quality. Are you using the analog output? And what kind
> of
> obstacles does the "mostly" refer to?
> 
> Regards
> Wolfgang
> 
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