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Old 07-15-2010, 08:15 AM
Ralf Mardorf
Default Transport issue for Qtractor - has impact to the jitter issue

Transport issue for Qtractor - has impact to the jitter issue
So the advice to use amidiplay is something I'll follow soon.

Hi all , hi Robin , hi Devin

Robin, for 64 Studio 3.3 alpha the group has got read and write access
to /dev/hpet too. Btw '[...] | sudo tee [...]' for 3.3 alpha isn't good,
regarding to the enabled root account. Anyway, for this recording test I
kept the value 64 for hpet/max-user-freq, but I'll test higher values
Devin and some others want to know if the drum module is played before
FluidSynth DSSI is played.

JACK2 doesn't start with -p4096, so I started JACK2 with -Rch -dalsa
-dhw:0 -r44100 -p2048 -n2 to increase the unwanted effect, to get a
clear result.

Without recording it's clear audible that the external drum module
always is played before FluidSynth DSSI is played, plausible regarding
to the audio latency (stupid idea to use such high latency , so
there's the need to do an audio test with lower latency, to see if
jitter might change what instrument is played first.

Instead of a rhythm I did record 4 to the floor at 120BPM to 'see' the

I did record FluidSynth DSSI by the sound card too. Left channel the
drum module, right channel FluidSynth DSSI and regarding to Qtractor's
graphic of the wavefrorms, there is jitter for both!

Ok, next recording with -Rch -dalsa -dhw:0 -r96000 -p512 -n2.

Without recording it's already audible that the drum module is played
first all the time ...

and it's visible too. Again there's jitter for both. The audio recording
of the drum module always is before the MIDI event. The recording of
FluidSynth DSSI sometimes is before and sometimes after the MIDI event.
There's no offset for the audio track.

I kept -Rch -dalsa -dhw:0 -r96000 -p512 -n2 and recorded FluidSynth DSSI
alone, internal Linux, without using the sound card.

The audio recordings are before the MIDI events and there's jitter. I
never noticed jitter internal Linux before.

I need to repeat the test ASAP, but by using 64 Studio 3.0 beta and
perhaps an older version of Qtractor.

Playing FluidSynth DSSI by MIDI and the recording made internal Linux in
unison, there isn't audible jitter. But after starting playing sometimes
MIDI and the audio recording are perfectly synced and sometimes there's
delay, real delay between the recording and MIDI, not only an early
reflection like effect (but without audible jitter, the jitter only is
visible by the waveforms).

$ qtractor -v
Qt: 4.5.2
Qtractor: 0.4.6

More maybe tomorrow.



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