On Wednesday 18 September 2002 19.18, Peter L Jones wrote: [...] > Well, when I had "-B 8,11" (8 x 2^11 byte buffers), the latency > was, um, rather amusing :-). Dropping this to "-B 4,4" means I > can't feel any latency between key press and sound.
That's really rather good for an off-line synth, I'd say! ;-) > (Dropping to > -B 3,3 caused very strange behaviour (that lead to an uncontrolled > reboot) Oops... If that's three buffers of 8 bytes, I'm not surprized - but still, the worst accident that should be possible (with SCHED_FIFO and no watchdog) should be a user space freeze. Was that what happened? > and -B 2,2 was too small - very strange noises produced.) Well, you should never use less than 3 buffers for anything if you can avoid it (applies to video as well, BTW), and you should probably stay above the minimum PCI DMA burstsize limit of 64 bytes. :-) > > (I'm talking about low latency mixing with live MIDI input, > > rather than playing back MIDI files with a large audio buffer. > > And no, I don't know how well timidity performs in this regard. > > Just pointing out some potential issues to keep in mind with any > > soft synth setup, basically.) > > Yup - my default set up is tuned for file playback, so it's tuned > to even out any problems caused by system performance. For manual > play, it needs to be tuned for low latency, which -B 4,4 appears to > achieve (at least, I've not yet come across further problems...). Well, buffering is obvious, but there's a *lot* more than that to it, if you want reliable real time performance. It's all about the design of the synth engine; chosing determinism before faster average speed, avoiding (standard) dynamic memory allocation, avoiding certain ways of talking to devices and other processes etc... //David .- M A I A -------------------------------------------------. | Multimedia Application Integration Architecture | | A Free/Open Source Plugin API for Professional Multimedia | `---------------------------> http://www.linuxdj.com/maia/ -' .- David Olofson -------------------------------------------. | Audio Hacker - Open Source Advocate - Singer - Songwriter | `-------------------------------------> http://olofson.net -' _______________________________________________ linux-audio-dev mailing list [EMAIL PROTECTED] http://music.columbia.edu/mailman/listinfo/linux-audio-dev
