What's the right way to do??? resample??

What's the right way to do??? resample??

[Joe Hsu]

    I am a beginner on Linux audio programming.

    When recording from one audio codec and playing
back from another audio codec in real time, there
must be some asynchronous problems.(Buffer overrun
for recording or buffer underrun for playback).
I believe this problem must have some answers.
Hence should I resample audio in real time dynamically
so that asynchronous conditions would be eliminated?
If so, what resample library would be suitable??
Libsamplerate or Libresample???
Thanks if anyone can give me some hints.
(My recording device is 8000HZ and my playback device 
also works at 8000HZ)
-- 
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Re: What's the right way to do??? resample??

[Dirk Jagdmann]

>     When recording from one audio codec and playing
> back from another audio codec in real time, there
> must be some asynchronous problems.(Buffer overrun
> for recording or buffer underrun for playback).
> I believe this problem must have some answers.
> Hence should I resample audio in real time dynamically
> so that asynchronous conditions would be eliminated?
> If so, what resample library would be suitable??
> Libsamplerate or Libresample???

There is now software solution to this problem, because software has no 
way to figure out, when/how much two hardware pieces get out of sync. 
You have to sync your hardware for input and output. That either means 
you have to use a hardware which provides both input and output and full 
duplex access or you have to use an external word clock cable to 
synchronisation. Then on the software side you can be sure, that your 
output will always consume the exact amount of data the input has just 
generated.

-- 
---> doj / cubic
----> http://cubic.org/~doj
-----> http://llg.cubic.org


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Re: What's the right way to do??? resample??

[Joe Hsu]

On Thu, 31 Mar 2005 16:36:15 +0200, Dirk Jagdmann <doj@cubic.org> wrote:
> You have to sync your hardware for input and output. That either means
> you have to use a hardware which provides both input and output and full
> duplex access or you have to use an external word clock cable to
> synchronisation. Then on the software side you can be sure, that your
> output will always consume the exact amount of data the input has just
> generated.

Thanks.

Actually I record from bt878 and play it back on AC97. So
what do you mean by "external world clock" in this case?
Is /dev/rtc an sort of external world clock? Or you just 
mean there is no solution without hardware modifications
in such a case??

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Re: What's the right way to do??? resample??

[Clemens Ladisch]

Joe Hsu wrote:
> On Thu, 31 Mar 2005 16:36:15 +0200, Dirk Jagdmann <doj@cubic.org> wrote:
> > You have to sync your hardware for input and output. That either means
> > you have to use a hardware which provides both input and output and full
> > duplex access or you have to use an external word clock cable to
> > synchronisation. Then on the software side you can be sure, that your
> > output will always consume the exact amount of data the input has just
> > generated.
>
> Actually I record from bt878 and play it back on AC97. So
> what do you mean by "external world clock" in this case?

In this case, there is no word clock; the hardware would have to
support it.

> Or you just mean there is no solution without hardware
> modifications in such a case??

You could either connect the TV card's analog output to the line in of
the AC97 so that both recording and playback use the same clock, or
you could convert the sample rate in software.  Most existing
libraries like e.g. libsamplerate assume that you know the exact
sample rate in advance, so you would have to write your own sample
rate converter that can adjust it ratio dynamically.


Regards,
Clemens



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