Re[4]: Midi looping

[miguel.barella@poyry.com.br (MAT)]

     Hi Greg,
     
     I am almost sure my JamMan is not broken (I will perform the test you 
     suggest to be sure) but the noise exists as confirmed by Bob Sellon 
on 
     the following mail:
     
     
     Message was resent -- Original recipients were: 
     To: Loopers-Delight <Loopers-Delight@annihilist.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
     
     ---------------------------------------------------------------------
     
     Robert S. Carter also listens to the glitch, see his mail:
     
     Y'know I never really heard the glitch so much until I went home 
after 
     reading your post and listened carefully. Now it's gonna bug the hell 
     out of me. Thanks a lot :). Some loops it's not so bad but yeah it 
can 
     be annoying. 
     
     ----------------------------------------------------------------------
     
     
     Anyway, I thik we have to live with it until some kind of upgrade 
     happens.
     
     Regards,
     
     Miguel
     
============================================================================

     
Miguel asked "How do you manage the annoying noise (sounds like a small   
glitch) that appears next to the loop boundary when the JamMan is   
receiving MIDI clock?
     
I tried to get rid of it with all kinds of tricks I could think of but 
did not succeed."
     
Miguel,
     
There must be something wrong with your JAMMAN.  Even if a loop is not   
spliced together perfectly there should be no added noise at the splice   
point.  Certainly if the end and begining of a loop are not either silent  
 
or matched perfectly you will here a glitch but this is not an added   
noise it is only what you here when you jump between two different sounds  
 
or tones.
Either you are not matching the end and beginning loops or you have a   
broken JAMMAN.
     
If you record a loop of silence you should find is that at the   
end/beginning of the loop(what I would call the splice point) is actually  
 
more silent then the rest of the loop.  If this is not the case and there  
 
is noise at the splice point therte is a problem with the machine.
     
Please let me know if you have any questions or if there is anything that  
 
I can do for you.
     
     
Best regards,
     
Greg Hogan
Lexicon Customer Service
Phone 617-280-0372
FAX 617-280-0499
email: ghogan@lexicon.com