More MIDI stuff

David Lee mymoog at ix.netcom.com
Sat Jul 4 00:48:29 CEST 1998


Also many unit's use a "soft thru". soft thru's can cause delays in the
midi chain, and can sometimes induce a delay that is 50ms or more. An
example of this type of synth is an Emax which allows it's midi "out" to be
used as a "thru" as well (controlled via internal software). If you try to
daisychain from one of these "soft thru" unit you may get an abnormaly high
amount of delay in the signal. Especially if the device is using alot of
the internal CPU for other things (i.e. CC meassages or Pitch wheel)

If this becomes a problem simply buy a MIDI Thru Box which will solve most
MIDI distribution problems.

David Lee

----------
From: media at mail1.nai.net
To: synth-diy at mailhost.bpa.nl
Subject: More MIDI stuff
Date: Wednesday, July 01, 1998 2:17 AM

At 11:47 AM -0400 06/24/98, Silence wrote:
>
>Also, the MIDI spec 1.0 says that the maximum recommended length for
>a MIDI cable is 50'.

Well, 49' if you convert it from metric :)

>After this, the capacitance of the cable rounds off the pulse edges too
>much to be useful.  When chaining together devices, the problem is less
>with losing data, than it is with the time delay becoming very noticable,
>i.e. the first synth sounds 50 milliseconds before the last synth, which
>is a VERY audible differnece.

No, the problem is losing data.  The only delay from a MIDI Thru is from
the optoisolator.  It is about 3uS.  To get a delay of 50mS you would have
to daisy chain over 16,000 MIDI Thrus.  Not even Vince Clarke has that much
gear :)

The limit on the number of MIDI Thru's is from distortion of the signal.
The rise of an optoisolator is only 3uS but it still isn't instantaneous.
So the cumulative effect of a number of optoisolators will shorten the time
of the individual bits eventually causing data to be lost.

PEACE OUT :)
MARK













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