Ubuntu 8.04 (under MacOS X) has occasionally "sound noi

[ebini]

Hi,

i'm using VirtualBox 1.6.4 on my mac mini (intel) with guest os ubuntu 8.04.

When i listen to music (p.e. amarok in the virtual machine) sometimes the music hangs or makes sound noise.

I tried to experiment with several parameters of virtualbox.
I also tried to test ALSA/PulseAudio/OSS.
There is no load or i/o-traffic on mac or the virtual machine.

Has anybody the same problem (and perhaps a solution).

Thanks.

Ebini

[TerryE]

If you search the various forums, you will see that getting high quality sound within a VM is very problematic. This is even more difficult than getting acceptable video. The reason is latency issues in the interplay between the host and guest kernels. The eye "sees" frames as ~25Hz and can tolerate the odd frame drop. The ear hears up to 20KHz and high quality playback is therefore digitised at 44KHz. The motherboard codecs only have small sample buffers so the audio device driver within the kernel must be scheduled at ~1000 slices per sec + in order to keep it primed. In the case of a virtualised OS this kernel driver is in fact running inside the VBox VMM process, and this must be scheduled at greater than this rate for this to work.

If this VMM isn't scheduled at this rate, then the codec will drop samples or sample segments and this is perceived by the ear as noise. You can tune up a VM to give acceptable playback performance, but this is a bit of a black art. People have reported a lot more success using USB based earphones and audio systems since these usually have local DSP chips and significantly larger input FIFOs to prevent such underrun.