Sample rate and playback speed

[David Aldrich]

I'm running QLab on OS X 10.8 with a Presonus FireStudio Project. I've noticed that sometimes my audio will play back about 10% slower than it should. I tracked the issue back to changing the sample rate while QLab is running as the issue. For some reason the Presonus defaults to 48kHz and to eliminate unnecessary conversion I change it to 44.1kHz but if I do it after I start QLab it messes with the playback speed.

Obviously this isn't really an issue since I now know to change the sample rate with QLab not running, but I thought it was odd. Seems like it's still doing a sample rate conversion but then playing back at a lower sample rate.

[Sam Kusnetz]

David Aldrich wrote:
> I'm running QLab on OS X 10.8 with a Presonus FireStudio Project. I've
> noticed that sometimes my audio will play back about 10% slower than
> it should. I tracked the issue back to changing the sample rate while
> QLab is running as the issue. For some reason the Presonus defaults to
> 48kHz and to eliminate unnecessary conversion I change it to 44.1kHz
> but if I do it after I start QLab it messes with the playback speed.

Hi David

There are a couple of things going on here, but the most important part
is what you've already discovered: you shouldn't change the sample rate
of your audio hardware while QLab is running.

That said, I've done that before with other audio interfaces and not had
a problem, so it's possible that this is an issue related to the
FireStudio more than with QLab. That may not be the case, but it may be.

Cheerio
Sam

--
Sam Kusnetz
QLab Field Operative
s...@figure53.com

[Chris Ashworth]

Thanks David,

I checked through the code and it looks like we’re catching the notification that the sample rate changed, but not trying to rebuild the internal structures that allow us to match playback to that rate.  Thus it is continuing to output at the old sample rate, producing the behavior you describe.

I’ll make a ticket in our issue tracker for this.

Best,

Chris