Re: MIDI & sysex stuff

[Xav <MBGE4MDC@fs1.ee.man.ac.uk>]

>> I can dig out all the relevent info if anyone seriously wants to
>> tackle this.
>
> I for one would be very interested in any information..
> (But I can't say I could write anything for MiNT[Net])

I'll try to remember to dig out what I can, and post it to the list 
for anyone to use (or for someone to keep for when this thread 
resurfaces in a couple of years ;)

>> Incidentally, the above could be solved if the synths were 
>> connected on a spur from the main loop. MIDI for music doesn't 
>> need a loop topology.
>
> What would that look like? I am just a little puzzeled about the 
> mechanics of MIDI - if you send something from a computer down a 
> MIDI cable, does it go down both the OUT and the THRU? (that is 
> prolly a stupid question...) If it does, then the MIDI IN port must 
> ignore the THRU signal and look only at the OUT...

Okay, here goes. Bluffers guide to MIDI connections, pt1.

Basically every MIDI device has at least an IN or an OUT. The IN is 
used for receiving information, and you can guess the rest. Most 
devices also have a THRU, which is basically a hard wired copy of the 
IN data (but after the opto-isolator at the IN). Usual topology 
therefore:-

    TRANSMITTER--->SYNTH1 IN=>THRU--->SYNTH2 IN=>THRU--->SYNTH3
    
Where ---> is a "real" cable, and => is a hard wired connection in 
the device. Often the transmitter is a computer running a sequencer. 
An important thing to note is that a synth may or may not have a 
keyboard, and even if it does, they will usually be treated as two 
separate devices. I.e. on most systems the OUT of the keyboard does 
not go directly to its synth section, but rather via a computer to 
its synth:-

    S1 KBOARD--->COMPUTER IN
    COMPUTER OUT--->S1 SYNTH
    
But the synth and keyboard are in one "box". Also there is usually 
only one keyboard, so you get:-

    KEYBRD--->COMPUTER IN
    COMPUTER OUT--->S1 IN=>THRU--->S2 IN etc.
    
This works because most MIDI messages are sent on a particular 
"channel" - one of 16. Each synth is set to respond to only one 
channel.

Due to the opto-isolators in the INs, the waveform can lose its 
integrity, so often a star topology is used:-


    TRANSMITTER--->IN=>THRU--->S1
                     =>THRU--->S2
                     =>THRU--->s3

Where the lump in the middle is a THRU box (one in, many THRUs).
A mixture can also be used:-


    TRANS--->S1 IN=>THRU--->IN=>THRU--->S2 IN=>THRU--->S3
                              =>THRU--->S4
                              =>THRU--->S5
                              
If you get what I mean.

Going back to the "spur" I mentioned yesterday, the final system 
would be:-


    +--->C1 IN==>OUT--->C2 IN==>OUT---+
    |                                 |
    +-------------+-------------------+
                  |
                  +--->S1 IN=>THRU---> etc.
                  
With this system, the synths could be used for playback (i.e. MIDI 
files), but with no connection back IN to any computer, could not be 
used for recording. Also anything played back by a computer would 
circulate forever (==> represents a software THRU) unless blocked by 
one of the machines.

Basically you _have_ to use one of these sotfware THRU arrangements, 
otherwise all the machines can listen, but only one can write to the 
network. Similarly there has to be a mechanism for blocking messages 
from circulating endlessly, not only network stuff, but other MIDI 
messages too.                  

If this isn't clear (I'm pushed for time), mail me, and I'll try 
again.

> I assume you can get hold of cable splitters to convert the MIDI OUT 
> of the Atari to be a MINI OUT and THRU? Could someone send the 
> technical info on how to build such a splitter?

You don't need one. _Every_ sequencer uses a software THRU, and there 
is no practical reason for needing a hardware version on a computer.

Cheers,

Xav

--
Xav
E-mail: mbge4mdc@fs1.ee.man.ac.uk                                      
Web: http://cerebus.lamp.ac.uk/~xav/xav.html
"It's who I am, it's what I do - I can't change" - Sledge Hammer