I'm encountering some strange behaviour. I'm running PD on linux (rh9 planetcCRMA) using maudio quattro sound card. It worked fine yesterday, but today I get amplitude overload and some errors. The test audio is distorted and I had to reduce the amplidute by factor of 10 in a patch I was working on to get acceptable levels. I'm using jack: jackstart -d alsa -d hw:1,0 -r 44100 which complains (semi periodically): *** alsa_pcm: xrun of at least {8.732-30} msecs
I ran the exact same thing yesterday with no (noticeble) problems and I haven't changed anything since.
Hi,
Oded Ben-Tal oded@ccrma.Stanford.EDU wrote:
I'm encountering some strange behaviour. I'm running PD on linux (rh9 planetcCRMA) using maudio quattro sound card. It worked fine yesterday, but today I get amplitude overload and some errors. The test audio is distorted and I had to reduce the amplidute by factor of 10 in a patch I was working on to get acceptable levels. I'm using jack: jackstart -d alsa -d hw:1,0 -r 44100 which complains (semi periodically): *** alsa_pcm: xrun of at least {8.732-30} msecs
I have no idea why you suddenly get this overloads, but you should *never* run Jack over a USB soundcard with a samplerate not divisible by 1000. So try with 48000 instead of 44100 Hz.
ciao
Frank Barknecht _ ___footils.org_
weird... why?
Frank Barknecht wrote:
I have no idea why you suddenly get this overloads, but you should *never* run Jack over a USB soundcard with a samplerate not divisible by 1000. So try with 48000 instead of 44100 Hz.
ciao
Hallo, Josh Steiner hat gesagt: // Josh Steiner wrote:
weird... why?
Because USB audio is delivered in frames of which there are 1000 frames per second. Running at 44.1 kHz means, that you have to pack 44.1 samples into one such frame. But there is no fractional sample so you pack 44 samples for 9 frames, then 45 sample for one frame, repeat ad infinitum.
This is not really compliant with how ALSA and Jack access the hardware, which is with a constant period size that, per requirement of Jack, also needs to be a power of two. With 44.1 kHz samplerate the driver has to do lots of buffering to emulate the changing frame fill which leads to masses of latency. For example, using 44.1 kHz on I never got the old Quattro running with anything less than 3 periods each with size 2024. Using 48 kHz samplerate this can be much lower. In fact with my current USB card, I can gow as low as "-n 3 -p 256"
Just try it, you will see yourself.
ciao
Frank Barknecht _ ______footils.org__
-
Frank Barknecht -
Josh Steiner -
Oded Ben-Tal