RE: JamMan & MIDI sysnc

["Sellon, Bob" <bsellon@lexicon.com>]

Miguel,

There are two possible causes for the noise I can think of; one you can   
fix the other you can't.

When Jamman is slaved to an external MIDI clock it determines the end of   
the loop by itself based on the tempo of the clock and the number of   
beats selected on the front panel. If the operator tries to end the loop   
manually, the resulting loop will very likely be shorter than it should   
be. When the loop is too short, Jamman restarts the loop twice: once when  
 
the end of the loop (time) is detected and once when the correct number   
of MIDI clocks has come in. The solution is to let Jamman close the loop   
by itself (DON'T tap a second time). This will get the loops size to it's  
 
best fit.

The second cause is based on the jitter on the incoming MIDI clocks and   
the resolution of Jamman itself. At best, Jamman can lock in a loop size   
to within half a millisecond (512us). The problem is that most MIDI clock  
 
sources have jitter (timing variations) in the same neighborhood. After   
the loop time is locked in, the priority in Jamman is to stay in perfect   
sync with the incoming MIDI clock. The problem is that the combined half   
millisecond resolution of Jamman and the jitter on the incoming clock   
result in the actual size of the loop changing very slightly every time   
through. As the loop size changes, Jamman either shortens the loop or   
replays the very beginning of the loop to compensate resulting in   
potential clicks and pops. With the PC itself being slaved the jitter   
gets worse and so do the clicks and pops.

As I said, there is currently no work-around for this other than, as you   
said, not playing anything at the loop edge. The only other thing I can   
suggest (which is equally klugey), is to place something percussive at   
the splice point which will tend to mask the noise. I am looking at the   
problem, however, and will let you know if I come up with anything.

If anyone out there has any suggestions on how to deal with this, I'd   
love to hear it.

Bob Sellon
Lexicon/Stec
bsellon@lexicon.com

 ----------
From:  Loopers-Delight[SMTP:Loopers-Delight@annihilist.com]
Sent:  Friday, April 25, 1997 12:56 PM
To:  loopers-delight
Cc:  ghogan
Subject:  JamMan & MIDI sysnc

     Hello,
       

     I am facing the following problem with JamMan, that maybe somebody
     already solved and can give me some help.
       

     An SMPTE track (from an ADAT) drives a PC with Cakewalk that sends
     MIDI clock to JamMan. Fine, JamMan syncs properly!
       

     The problem is that in the beginning of every bar and/or loop JamMan  
 

     introduces an audible perturbation on the sound. The silly solution   
I
     found is not to play in this spot but this keeps me away from
     continuos sounds and many other things.
       

     This does not happen when Jam Man is used alone or driving the
     computer or any other box.
       

     Any clues on how to solve this?
       

     Miguel