I recompiled S60 Platform: Sound Mixer Example v2.1 with only one red box flaying on screen (changed only for statements in DoTimer function) and with turned off background music.
When I run this on various devices I observed some performance problems:
on N82, N95 everything works fine without delays
on E66 there is delay between moment when red box hit edge of the window and sound is played
on 5500 there is longer delay than on E66.
I also created my own sound mixer using CMdaAudioOutputStream Symbian IPC, and in one thread. Performance is better than this one from example but on both E66 and 5500 there is still delay between moment of calling play of sound sample and speaker sound generation. I think this is because on 5500 and E66 sound subsystem has lower hardware performance than on N82, N95. Is there other way of playing mixed sound on Symbian phones than CMdaAudioOutputStream?