Re: plughw versus hw

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Hi Pierre Habraken!

 On 2011.06.20 at 19:32:28 +0200, Pierre Habraken wrote next:

> I can imagine that this is a FAQ, but I could not find a clear answer : 
> which precise difference(s) distinguish(es) plughw and hw from each other ?
> Does plughw apply sound processing that hw does not ?

plughw *might* apply simple sound processing if needed, mostly channels
conversion and rate conversion if required. It doesn't have to apply
processing.
hw doesn't support such processing only works when operating strictly in
mode that audio card support.

If you have device that supports only 2 channel, 16 bit 48000 mode then
"hw" device won't be able to playback 2/16/44100 stream, or mono stream
for example; you'll get an error when you try. But plughw will accept
such streams and do the conversion. However, if you use plughw and
output 2/16/48000 stream then no conversion is needed and most likely
plughw won't be doing any processing.

Note that using both hw and plughw can lead to specific problems, so
it's best to use "default" device unless you have very specific
requirements.

-- 

Vladimir

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