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From: ach@pucc-h (Stephen Uitti)
Newsgroups: net.music.synth
Subject: MIDI and RS232
Message-ID: <1854@pucc-h>
Date: Tue, 19-Feb-85 11:55:03 EST
Article-I.D.: pucc-h.1854
Posted: Tue Feb 19 11:55:03 1985
Date-Received: Fri, 22-Feb-85 08:25:16 EST
Organization: Purdue University Computing Center
Lines: 33


	9600 Baud is indeed 9600 Bits/sec.  Usually, its something like
8 data, 1 start & 1 stop bits.  10 bit times per useful byte.  Thus
9600 baud is 960 cps (Characters per second).  Thus, MIDI is a lot
faster than 19200 baud.  However, a note sent via MIDI takes 3 (8 bit)
bytes (a byte still has the 2 bit overhead, I think).
	MIDI data only gets sent when something happens.  Since you
don't play 6 millisecond trills, the MIDI line tends to be quiet most
of the time.  The main problem with translation to a half speed media
is that timing is a concern.  One byte at 19K baud takes (roughly) half
a millisecond.  MIDI uses three bytes for each note action.  This
translates to 1.5 milliseconds for 19K baud serial.  In chords and
other "simultaineous" events, the inter-note timeing becomes more
important.  The human ear tends to be able to detect differences of
something like 6 milliseconds (if memory serves).
	The three bytes specify velocity and pitch.  When the note is
released, you also specify velocity and pitch.  If you are not
interested in velocity information, then the data that must be sent can
be done with fewer bytes, and thus quicker.  With this sort of
sacrifice (for some instraments, velocity would be ignored anyway), one
can do equally well as MIDI with just a 19K baud serial port.
	A straight translation can be done to 38K baud serial.  There
are UARTS that will let you do this kind of speed.  In fact, normal
UARTS are used for MIDI.  There is then additional hardware to do
opto-isolation.
	Sequential Circuits will sell you a MIDI spec, for $10.00.
It's not a high quality book, but it talks about MIDI in a technical
black-and-white manner.  Unfortunately, I don't have the address
handy.
	Perhaps when I write a review of my Prophet-T8, I'll give the
Sequential address as well.
	Stephen Uitti, UNIX support staff, Purdue Univ. Comp. Center
ps:
	Various buzzwords are copyright/trademarks of various organizations.