[sdiy] MIDI Router

[ASSI]

On Samstag, 11. April 2009, Matthew Smith wrote:
> After working out that I would need more MIDI interfaces than I
> have USB ports on my [Linux] laptop (will be running the Qtractor
> DAW,) I had another look at my gear to see what I really needed. 

If you're laptop-centric anyway, why not get as many 8x8 USB MIDI 
interfaces as you need and aggregate them via a USB2.0 hub (make sure 
the computer talks to the hub in highspeed - not all hubs can do 
highspeed<->fulspeed translation).  All routings can then be done with 
aconnect (under Linux, part of ALSA/alsatools) and changed at a whim.

If you really just use one module at a time you could also use a MIDI 
Thru / MIDI Merger combination, but it is not likely to be less 
expensive and certainly less flexible should you change your mind 
later on.

> * Backing up modules using MIDI SysEx - need as many MIDI ins to
> laptop as there are modules doing this.

Check

> * Recording patterns from the Alesis to either the laptop or the
> workstation (in real time.)

Check

> * Latency from using MIDI through.

Check

> * MIDI routings getting to damn complex. Example: why am I not
> getting MIDI data on unit x?  Because it's at the end of the MIDI
> through chain and one of the units in the middle is switched off.

Check.

> The logical solution would appear to be to have the MIDI ins and
> outs of every unit connected to a single patch/hub/router or
> whatever you want to call it.  Every in can be routed to every out.

Check.

Without the computer you'd need something like a Waldorf MIDIbay or a 
MIDItemp PMM88E/MT16-X.  You can only get these used these days, but 
the laptop in the above setup could be replaced by an embedded uC 
board running Linux.  Even if you don't intend to replace the laptop 
you should probably have a look at how things have been done by the 
hardware MIDI routers.  Especially the MIDItemp stuff is very deep and 
allows quite elaborate setups as you can filter data at the input 
and/or the output and set up multiple filters at once.

> An simple 8 in x 8 out unit could be built simply by using a
> 74HC151 mux for every output and a microcontroller (or possibly 2
> microcontrollers - cheaper than using latches!) to control them. 
> By multiplexing the multiplexers (say with 74HC157s) we could
> easily go to a 16x8 or, by duplicating the 74HC151s as well, having
> a full 16x16 unit.

This only works if you don't need to merge MIDI (i.e. never).  I 
believe this is what the Kawai MAV8 MIDI patchbay did: you have four 
inputs and can send them to any of eight outputs, but only one at a 
time.  This works well for controlling modules from a set of 
keyboards, but not at all for getting data back from the modules.

> The uCs could be controlled from some sort of front-panel control
> and/or MIDI.  (Add another 74HC151 and we could select not just the
> MIDI channel used to control the device, but the port as well.)
>
> My main question is which MIDI controller would I use for selecting
> patches? (Note that an 8x8 or a 16x8 unit would work fine here but
> a 16x16 could complicate the MIDI implementation if we only have 7
> bits from which to select.)

Bank Switch MSB/LSB + Program Change gives you 21 bits to play with.



Achim.
-- 
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