About DSP API

Sylvain Munaut 246tnt at gmail.com
Sat Dec 3 15:31:51 UTC 2011


> So, does the dsp_api.ndb->a_du_0 member hold the audio data to be send to
> the other peer, or that's something else?  How can I capture the audio data
> (after codec), make a slight modification to that data, and send it to the
> other mobile?

Mmm, I'm not sure you can do that. You can 'peek' at the audio, but by
the time you see the data there it may have been processed into TCH
frames already.

When in 'PLAY_MODE', it will take data to send from a_du_1  (in
TCH/F). So it's possible that the data from the microphone would still
be in a_du_0 and so you could put it in play mode, do your
modification by copying data from a_du_0 to a_du_1 ...

As I said : No documentation so it's all been done by error / trial,
you'd have to try :)

> I can see that AUDIO_TX_TRAFFIC_REQ/AUDIO_RX_TRAFFIC_IND
> audio mode were created for that purpose, but I'm not sure how to use that.
> Do I need to make the modifications I need on gsm_recv_voice and
> gsm_send_voice (voice.c)?

Those are used to RX and TX frames from the host (rather than the
phone directly). The only way to use them "as is" is to interface
osmocom-bb with LCR (not sure if there is a howto ...).
But as you saw in voice.c you could modify the code yourself to feed
data if need be ...

Cheers,

    Sylvain




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