Re: [proaudio] Real-time for audio

[Gavin Pryke <gavinlee303@xxxxxxxxxxxxxx>]

On Tuesday 04 May 2010 17:03:56 Grant wrote:
> I'm trying to set up a real-time system for audio playback via mpd.
> I've booted to rt-sources with CONFIG_PREEMPT_RT enabled.  Do I need
> to set up jack and follow the real-time instructions here:
> 
> http://jackaudio.org/faq
> 
> Is there anything else I need to do?
> 
> - Grant

Hi there

I'm not familiar with mpd at all but a realtime kernel for this seems a bit 
overkill. The way I see it is a realtime kernel is tuned for low latency 
interactivity for things like soft synths, effects and where you need the 
responsiveness of live input with minimal delay.

The reason is because playing a soft synth live via a midi keyboard is just 
unplayable when you have say a hundred millisecond delay from playing a note 
until when you actually hear it. With a realtime kernel you can get very low 
latency and soft synths and the like become much more usable. For a daemon 
playing music I don't see how this would make much difference but as I say I'm 
not familiar with mpd.

It seems you went down the right track though, one thing I might add is that 
if you followed the jack faq, you need to add yourself to the audio group to 
have realtime functionality for processes that you run. Or you could add the 
username that mpd runs as to limits.conf instead, however I'm not sure of the 
consequences of this.
Hope this helps and the best of luck in your endeavour.

Best regards
Gavin