Hitchhiker's Guide to Openbsd

How do I setup aucat(1)?
There's no configuration file and, in most cases, no tweaking is needed. Typing: 
$ aucat -l
will start the server on the default audio device (the one the 
/dev/audio
symlink points to) running at 
44.1kHz and using two channels (stereo). This means that applications using stereo at 44.1kHz will run 
optimally, i.e. without triggering conversion code. If the device doesn't support those parameters, 
aucat
(1)
will automatically pick another set of parameters. 
If you start aucat as root, it will increase its priority, to decrease the probability of buffer underruns or 
overruns. It can be started at system boot by appending: 
aucat_flags=""
to 
/etc/rc.conf.local
. 
What latency do I need?
The latency is the time between when a program takes the decision to play a sample and when the user 
hears the sample. Since audio data is always buffered, this delay is proportional to the audio buffer size. 
The following values are recommended: 
http://www.openbsd.org/faq/faq13.html (9 of 25)9/4/2011 10:02:21 AM

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13 - Multimedia
●
Real-time synthesizers: 5ms. This is the time it takes between hitting a key on your MIDI 
keyboard and actually hearing the note. Roughly, 5ms corresponds to the time it takes for the 
sound to propagate 1.75m. 
●
Games: 50ms. This is the time between when you see an event and you hear the corresponding 
sound. 
●
Movie players and alike: 500ms and more. Such applications ``know'' the sound to play in 
advance, and send audio data in such a way that it is played simultaneously with the 
corresponding picture. 
The smaller audio buffers are (to achieve low latency), the larger the probability to overrun/underrun is. 
Buffer overruns/underruns result in ``stuttering'' of the sound. 
In server mode, aucat(1) imposes a minimum latency on all audio applications, and the default latency is 
around 250ms. If you plan to use applications that require a lower latency, use the ``-b'' option to select 
the desired latency (expressed in number of frames). For instance, at 44100 samples/second, 50ms 
latency corresponds to: 
44100 samples/second x 0.050 seconds = 2205 samples 
then run 
aucat(1)
as follows: 
$ aucat -b 2205 -l