2011/11/6 Paul Davis <[email protected]>: > On Sun, Nov 6, 2011 at 2:20 AM, Emanuel Rumpf <[email protected]> wrote: >> 2011/11/5 Iain Duncan <[email protected]>: >>> On Thu, Nov 3, 2011 at 8:05 PM, David Robillard <[email protected]> wrote: >>>> >>>> >>>> The only difference non-jack would make is you need some function to >>>> tell you roughly what audio time it is you can call from another thread. >>> >>> Does one use the system clock for that? >> I think frame time (a frame of samples) is meant here ? That time is >> delivered in the jackd process callback. >> >>> Is it accurate enough? >> Depends on the system clock used, I presume. >> For best accuracy, you have to configure your kernel to support HPET >> (high precision event) timers >> and make ALSA use it as default. > > the clock used for the system clock is less important than using a DLL > to "link" the audio clock and the system clock. this enables you to > answer the question "if its time T on clock1, what time is it on > clock2?" > > fons wrote the canonical paper on this for a Linux Audio conference a > few years ago, and JACK contains a DLL for this purpose > (jack_get_microseconds() will return a prediction of the current time > according to the audio clock, based on the system clock and the DLL. >
Thanks for the hint, Paul, and to Fons of course. An interresting paper, found it here: http://kokkinizita.linuxaudio.org/papers/index.html Still, I wonder: Why not compute the time of any sample - relative - to a random start time (using sample frequency) ? ( The start time would be the time, a recording or playback was started. ) For example: At f = 48000 Hz, I would expect a soundcard to deliver exactly 48000 * 10 = 48E4 samples in 10 seconds. Is this assumtion wrong ? If this applied, one could easily calculate the time-position of Sample S = 96000 based on a random start time (offset) T0 = 10 seconds: (We know the answer : 10 sec + 2 sec = 12 sec ) Calculation: 1 sec / 48000 Hz * 96000 + 10 sec = 12 sec (position of sample nr. 96000) -- E.R. _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
