[alsa-devel] ALSA synchronization

arif setiawan n.arif.setiawan at gmail.com
Sun Aug 23 03:15:16 CEST 2009


Thank you for the input. I think we have been neglecting digital-analog
conversion issue until now. We don't have any experiences in broadcast a
digital data over an analog channel.

I think we should learn encoding, modulation and error correction now using
google and others. That being said, I think this is not ALSA domain,
however, any references and working example would be helpful for us.

Thank you,

Best Regards


On Sun, Aug 23, 2009 at 5:10 AM, James Courtier-Dutton <
james.dutton at gmail.com> wrote:

> 2009/8/22 arif setiawan <n.arif.setiawan at gmail.com>:
> > Hi,
> >
> > We are working on audio processing (encryption-decryption) and audio will
> be
> > sent using radio.
> >
> > Our configuration is :
> >
> > Audio source - ALSA audio in - encryption - ALSA audio out - transmission
> > over radio (now we still use audio cable) - ALSA audio in - decryption -
> > ALSA audio out - speaker.
> >
> > So data will be sent through radio channel and its converted to analog
> form
> > by ALSA PCM during playback. We want to solve synchronization issue by
> using
> > data header so that we can decrypt correct data block. So far we still
> > unable to verify that data we received in the decryption side is similar
> to
> > data that we sent from encryption box. Supposed that we filled buffer in
> > encryption box with some values, when we check buffer in decryption box,
> we
> > can't get same data. Our guess that data somehow changed in
> > digital-analog/analog-digital conversion or we might make mistakes in
> > filling the buffer so data is not compatible with ALSA PCM.
> >
> > Any suggestion to solve this problem?
> >
> Where is the conversion from digital to analogue on the output direction?
> Where is the modulation and error correction happening on the radio
> bit, in between the encrypt and decrypt steps.
> You should probably do a test without the encrypt and decrypt stages,
> and just ensure the input equals the output.
> Kind regards
> James

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