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Holger Freyther holger at freyther.de> On 30. May 2017, at 09:43, Mychaela Falconia <mychaela.falconia at gmail.com> wrote: > > Holger Freyther <holger at freyther.de> wrote: Hi > What exactly are the bits which you send and receive every 40 ms? Do > you get two 260-bit GSM 06.10 codec frames every 40 ms, with the > ability to send your own arbitrary bits into the TCH uplink, including > the possibility of passing non-speech data over voice TCH if the > network does TFO as in GSM 02.53? The latter is what the Calypso DSP > allows. It is alaw. I assume the Qualcomm DSP will do the transcoding but I didn't look/trace the implementation (and the UC20 doesn't run Linux). E.g. I used this to play a sine wave on a connected call. gst-launch-1.0 audiotestsrc wave=sine ! audioconvert ! audioresample ! audio/x-raw, rate=8000, channels=1, format=S16LE ! filesink location=/dev/ttyUSB1 sync=true