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From: scott@bbxsda.UUCP (Scott Amspoker)
Newsgroups: sci.electronics,comp.music
Subject: Re: MIDI data compression idea
Keywords: MIDI
Message-ID: <1347@bbxsda.UUCP>
Date: 15 Nov 90 21:08:37 GMT
References: <1990Nov15.173346.11644@yenta.alb.nm.us>
Reply-To: scott@bbxsda.UUCP (Scott Amspoker)
Organization: Basis International,  Albuquerque, NM
Lines: 42

In article <1990Nov15.173346.11644@yenta.alb.nm.us> dt@yenta.alb.nm.us (David B. Thomas) writes:
>All this talk of interfacing MIDI to PC serial ports got me thinking:
>
>Aren't MIDI messages horrendously inefficient?  I seem to remember
>reading that normal note data, in order to be distinguishable from
>control messages, has to have the eighth bit turned off.  But the
>data is still logically grouped in eight-bit chunks, so you get
>something like this:
>
>0000xxxx
>0000yyyy
>
>where "xxxxyyyy" is the actual data byte.
>
>Of course, the control messages use the other bits, but they still appear
>compressable.  I'll bet with a smart midi card doing hardware compresssion
>(and buffering), you could cut the throughput of actual bits down to 19.2k
>and not lose any (valid) information.
>
>						Comments?
>
>						little david

MIDI command bytes have the 8th bit on.  MIDI data bytes have
the 8th bit off.  I know of no MIDI command or data that
disregards the upper 4 bits.  All in all, the MIDI data
format is pretty efficient.  However, sequencer files
are likely to contain recurring "patterns" of data that
would benifit from a compression scheme.

Also, bulk dumps must frequently transfer 8-bit data within
the 7-bit data bytes.  This is left entirely to each manufacturer.
Some manufacturers are lazy and simply do a hex transfer (I assume 
that's what you were describing).  Others send 7 bytes of 7-bit data
followed by an 8th byte containing the hi bits of the preceding 7 bytes.
This 7/8 effeciency ratio seems OK to me.

-- 
Scott Amspoker                       |
Basis International, Albuquerque, NM | "I'm going out for a sandwich"
(505) 345-5232                       |                       - Ben
unmvax.cs.unm.edu!bbx!bbxsda!scott   |