On Sun, October 5, 2014 22:25, Fons Adriaensen wrote: > On Sun, Oct 05, 2014 at 08:39:11PM +0200, [email protected] wrote: > > >> As a scenario, at point a) an analog signal is injected that will be >> played back (analog) at point b) with the lowest possible (and constant) >> latency. How do you intend to handle diverging clocks of the audio >> interfaces (ADC/DAC) at both (a/b) ends? >> > > Either > > > 1. Sync the HW sample rates to an explicit or implicit reference > provided by the network protocol. Requires special audio HW. A few normal > audio interfaces (e.g. some RME cards) would allow to do this as well, but > I know of no software that uses this > capability. >
Sounds interesting. I asked myself if it would be possible to drive the audio interface clock by the host (not by a wordclock coming from another audio interface which makes the "network" case local again to some degree), i.e. through ticks sent via FW/USB. > 2. Resample at the receiver, as njbridge does. > i know this, a real pearl! It's working amazingly well. The data on the receiver is not 1:1 equal to what is being sent. This works for most cases though. > > 3. Use some other trick. E.g. for VOIP a classical one is to > modify the lenght of the pauses between words or phrases. > Interesting approach :) Imagine this: Many middle-class audio interfaces have an S/PDIF input that can drive the internal clock (interface is slaved to S/PDIF). S/PDIF is rate-less, any (?) rate would work. Now, if we'd have an external device that does nothing else than providing a variable clock to the audio interface via S/PDIF, software-controlled, it would be possible to match / align decoupled, network-connected hosts. Scenario: endpoint audio interface is slaved to that variable "speed" S/PDIF generator, that is software controlled. Some clever tool could then adjust the speed to match the sender's rate. This would allow non-resampled ~isochronous audio on remote hosts for cheap. The S/PDIF protocol looks relatively simple (~5 MHZ bit by bit output for SR 44100 needed though). Unfortunately this hack is beyond my skills (if it would work at all). Cheers Tom _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
