Read and write different buffer sizes

Read and write different buffer sizes

[Elias Kokkinis]

Hello all,

I would like to ask if it is possible in ALSA to define different buffer sizes in the input and output streams.

I am using PCM sound and I want to read 2048 samples, do some processing involving overlap-add and then keep 1024 of them and put them to the output. And so on...

So I want to have the same sample rate and everything but different buffer sizes. Is this possible? I have tried an implementation of this, but I think the output for some reason still outputs 2048 samples and the audio is choppy, like having 1024 samples of audio and 1024 of silence.

I don't know if I am making myself clear here, maybe it's the 10 hours of work up to now, but anyway any help/comments would be greatly appreciated.

Elias Kokkinis

Re: Read and write different buffer sizes

[Clemens Ladisch]

Elias Kokkinis wrote:
> I would like to ask if it is possible in ALSA to define different
> buffer sizes in the input and output streams.

Yes.  (But which buffer sizes are allowed always depends on the
hardware's capabilities.)

> I am using PCM sound and I want to read 2048 samples, do some
> processing involving overlap-add and then keep 1024 of them and put
> them to the output. And so on...
>
> So I want to have the same sample rate and everything but different
> buffer sizes. Is this possible? I have tried an implementation of
> this, but I think the output for some reason still outputs 2048
> samples and the audio is choppy, like having 1024 samples of audio and
> 1024 of silence.

Regardless of the buffer size, when both devices run at the same rate,
you must output, on the average, as many samples as you have read.


Regards,
Clemens

Re: Read and write different buffer sizes

[Elias Kokkinis]

Clemens, thanks for your reply.

Do you think there is a way to accomplish this using different period sizes in input/output? I haven't exactly grasped the way ALSA reads and writes yet, so I have a difficult time planning how to do this...

Elias

On 13 Jan 2012, at 17:01, Clemens Ladisch wrote:

> Elias Kokkinis wrote:
>> I would like to ask if it is possible in ALSA to define different
>> buffer sizes in the input and output streams.
> 
> Yes.  (But which buffer sizes are allowed always depends on the
> hardware's capabilities.)
> 
>> I am using PCM sound and I want to read 2048 samples, do some
>> processing involving overlap-add and then keep 1024 of them and put
>> them to the output. And so on...
>> 
>> So I want to have the same sample rate and everything but different
>> buffer sizes. Is this possible? I have tried an implementation of
>> this, but I think the output for some reason still outputs 2048
>> samples and the audio is choppy, like having 1024 samples of audio and
>> 1024 of silence.
> 
> Regardless of the buffer size, when both devices run at the same rate,
> you must output, on the average, as many samples as you have read.
> 
> 
> Regards,
> Clemens
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