[iiwusynth-devel] Iiwusynth on windows, latency measurements

[M. Nentwig]

Hello,

iiwusynth_debug.exe works on Windows 98. Nice job, Peter!
Now that was a good reason to do long-overdue latency testing:

Midi data was sent from one keyboard into a sound module, MIDI thru
connected to the MIDI input of iiwusynth.
Both outputs were recorded, and the time difference measured. Four
samples were taken per measurement.

Windows, UA-1 USB audio interface: 60..63 ms
Windows, on-board sound chip, Maestro3: 55 .. 57 ms
Linux, UA-1 USB interface with kernel default audio.o driver: 30..33 ms
Same with only one ? buffer (-c 1 option): 12..17 ms
Linux, UA-100 with customized low-latency driver: 11..13 ms

The Linux and Windows versions of iiwusynth differ in their default
audio queuesize setting (iiwusynth.h). Is that setting used somewhere?
Still, I wonder what makes the Linux version four to five times faster
than its Windows counterpart:

http://www.cakewalk.com/DevXchange/audio_i.htm
"Unfortunately, this power comes at a price. Due to internal buffering
KMixer nominally adds 30 msec of
 latency to audio playback streams. (At present, Microsoft does not
provide a method to allow host
 applications to bypass KMixer.)"
the same at
http://linux.oreillynet.com/pub/a/linux/2000/11/17/low_latency.html

Looks like Windows is unable to deliver sufficient performance on
non-pro (i.e. lacking ASIO driver) hardware. Sequencing should work fine
(win-iiwusynth is a lot faster than other software synths I've seen so
far, with latencies up to 500 ms), but real time playing is still
impossible at the moment.

Cheers

Markus