linuxaudio.org

On Sun, Nov 6, 2011 at 2:20 AM, Emanuel Rumpf  wrote:

quoted text
> 2011/11/5 Iain Duncan :

>> On Thu, Nov 3, 2011 at 8:05 PM, David Robillard  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.

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