Hi Danilo, FreeDV does assume no missing (or gained) samples in the modem signal, on both the Tx and Rx side. This implies good sync between the USB sound card and the host Machine. I would hope the USB sound card sets the sample rate. Otherwise in FreeDV you will lose frame sync (which is quickly recovered I guess).
Less important for speech I/O as us humans don't care much about a missed or gained chunk of 20ms samples. A bug from last year in this area: https://www.rowetel.com/?p=6041 It would be good to try a test for this. In the past I have connected a couple of PCs (one with a USB sound card) over FreeDV for an hour with no loss of sync. Must try that again some time. Cheers, David On 20/02/19 16:25, Danilo Beuche wrote: > Hi, > > On 20.02.2019 06:17, Alan Beard wrote: >> >> *"SmallDV" uses only one audio device so, cannot get into buffer >> problems * >> *because of different sample rates, in and out.* >> * >> * > > this is unfortunately not exactly true. SmallDV reads audio data from > the USB device into the computer, and both have different clock domains, > i.e. there is already a (small) mismatch. And the same applies in the > opposite direction (computer to audio). USB audio has different modes > for handling this issue but all of them require both sides (USB device > and USB host) to do it properly together, see for instance > https://www.electronicdesign.com/embedded/achieving-bit-perfect-usb-audio . > > The UHSDR firmware suffers from this problem, since we have not > implemented the clock synchronization (properly) and depending on the > clock differences this creates audible issues in the audio streams in > regular intervals. However, as far as I have seen it, it does not cause > real problems, for instance if used with FT8 or FreeDV. > > Regards, > Danilo > > > > > > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
