Am Sonntag, 5. Oktober 2014, 23:35:21 schrieb [email protected]: > 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. > just to add another options and be a wiseacre :
On a microchip dsPIC [1] you can adjust the internal oscillator (RC) (where also the sample clock for DA is derived) in a small range of 10%, so it is possible to use PTP for sample-exact synchronization (I did do a "soft PLL" for a low cost solution of a DA to avoid re-sampling and big buffers). I was told on ARMs Oscillator tuning is also possible, and if audiohardware derives clocks from it, it can also be tuned and used as soft PLL. Anyway there are Chips [2] which can generate sample-clocks (Master-Clock) from a PTP signal, so if your audiohardware supports Master-Clock, you can add such a chip ;-). Anyhow PTP aware switches are only needed if absolute time is important (tracking systems), so with a constant latency, PTP also over a Switch border is no problem for sample accurate synchronicity, a router could be a bigger problem. [1] http://ww1.microchip.com/downloads/en/DeviceDoc/39700c.pdf page 10 [2] http://en.wikipedia.org/wiki/List_of_PTP_implementations#silicon mfg winfried _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
