[alsa-devel] Noisy audio - ALSA Configuration

Iovescu, Magdalena m-iovescu1 at ti.com
Thu Aug 16 01:27:00 CEST 2007

>> Does anyone have examples or documentation on how to configure
>> frames and buffers for various sample rates? I am writing a
program to
>> route a mp3 decoder output to ALSA on an ARM processor, and I
get noisy
>> audio. For a CD quality stream (S16_LE, 44100 kHz, Stereo, 128
bps) I am
>> using an output buffer of 44100 bytes, a period of
44100/(channels*2). With
>>Be careful about the distinction between bytes and frames (i.e.
>>a frame of stereo S16 is 4 bytes)
>Start with the period 
>1024 frames =  4096 bytes
>then make your buffer at least 2x this:
>8192 bytes
> (I'm not an app developer, so others may jump in with a better
>Did you look at the code in alsa-lib/test?
Thanks Eliot, I will try this buffer size. 
I did look at alsa tests, but I was not too convinced, as when I run
those apps I still got plenty of short writes. Would someone please
explain why do these 'short writes' occur?
>> a buffer this big, I do not get underruns, but I do get all
short writes. I
>> have not been able to find the right configuration to avoid
short writes,
>> and more importantly, to get good quality audio. What do
'short writes' (I
>> am using writei) really mean? Is this a performance issue in
the driver, or
> is mainly because of buffer setup? I would really appreciate
any help with
>> this.
>> Magdalena


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