Emu XL-7 & MP-7 User's Group

--- In xl7@yahoogroups.com, Aaron Eppolito <synthesis77@y...> wrote:
> > In response to numerous comments about how tight the sequencer 
timing
> > is on the XL/MP, here are some concrete timings. Executive 
summary:
> > the timing accuracy varies from superb to unusable, depending on
> > circumstances.
> 
> This looks an awful lot like the tests we did with a few storage 
scopes
> and wave editors.  We did this a lot when we were trying to bring 
down
> the pattern change time (the 1.11 release).
> 
> > * Factory pattern, tracks 1-15 running with volume=0, track 16 as
> >   test track: drift routinely at 10msec, worst case around 24msec.
> 
> Even when the volume is 0, internal tracks (int or both) that are
> unmuted still have to play the synthesizer.  This is in case the 
volume
> is turned up while the notes would still be playing.  Therefore, 
you're
> limited more by the synthesizer.  Note-ons take a finite amount of
> time, depending on number of voices the note fires.
> 
> Note also that this is not "drift", it's "jitter".  Drift implies
> cumulative error (i.e. after several minutes, drift adds up).  
Jitter
> implies non-cumulative error (i.e. several minutes later, it won't 
be
> any worse than it was at the beginning).
> 
> Also, it should be very "deterministic", meaning that the same notes
> each time will be delayed the same amount (or very close).  While 
this
> doesn't sound like it matters so much on paper (or email?), it does
> when you're listening to your pattern.  It means that if you're 
hearing
> something that's sloppy, you can fix it; and conversely, if it 
sounds
> good, it won't suddenly behave badly later.
> 
> Lastly, for a given note, higher numbered track performance will 
only
> degrade if there are notes at that exact timestamp in earlier 
tracks. 
> Translation: the track doesn't necessarily matter, just how many 
notes
> are at the same timestamp on lower numbered tracks.  It is, however,
> very good practice to put the most important things (timing-wise) on
> early tracks.  Save those later tracks for pads, noises and other
> instruments with longer attack times.
> 
> > Data in other tracks doesn't influence performance if the
> > tracks are muted. (I have a feeling this wasn't true of
> > OS 1.31, but could be wrong.)
> 
> That's correct, muted events take nearly no time at all.  This has 
been
> that way, I believe, from the 1.00 release.
> 
> > Interestingly, turning MIDI on for the tracks ("ext"/"both")
> > doesn't seem to make much difference. The XL-7 seems to have
> > bandwidth/performance issues internally, regardless of the
> > external MIDI traffic.
> 
> Right.  Turning the synth *OFF* however, will make large amounts of
> difference.  Try setting all your tracks to ext (not both) except 
for
> the test track and see how it fares.  This is a more accurate test 
of
> the *sequencer* alone.  Also, you can do the inverse, play your test
> sequence in from an external sequencer with all but the test track's
> volume down.  You'll probably get similar results (possibly even 
worse
> due to MIDI bandwidth) to your internal tests.
> 
> > A second set of timings tests the arpeggiator: this time, the
> > sequence is four quarter-notes (300 ticks long), but the preset
> > repeats at 1/16 notes.
> > 
> > * Test pattern as track 1, others running volume=0: routinely 
8msec,
> >   often around 15msec.
> > 
> > SUMMARY: in ideal circumstances (sparse data), the arpeggiator has
> > slightly better timing than the sequencer, but it degrades equally
> > badly when other tracks are active, and -- curiously -- lower-
> > numbered tracks are apparently *NOT* prioritised, so there's no
> > clear way of improving critical arpeggiator timing in a busy 
pattern.
> 
> The sequencer has priority over the arpeggiator.  If you've got 
other
> notes firing (again regardless of volume) at a given instant, the 
ones
> from the sequencer will happen first.  The easy way to give the
> arpeggiator a head start is to slide the trigger notes back a tick 
or
> two in the sequencer.
> 
> Hope this clarifies stuff a bit!
> 
> -Aaron
> 
> 
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I hate to be like my management, but...:  the science is interesting, 
but is there a fix??

zsk