[sdiy] MIDI notes filter which is also a MIDI converter for Junos ?

rsdio at sounds.wa.com rsdio at sounds.wa.com
Sun Dec 29 02:25:31 CET 2013


I prefer to encourage DIY efforts, but this design violates the MIDI  
specifications in multiple ways.

First of all, there is no opto-isolator on the MIDI input, which  
risks ground loops between your synthesizers. Is there any reason you  
did not use the standard chip?

Second, powering a circuit from the MIDI cable is a hack that was  
never sanctioned by the MIDI Manufacturer's Association (to my  
knowledge - if it has been added to the spec, please let me know). In  
this age of 3.3V devices, there's no guarantee that a MIDI output  
will actually be 5V. As long as a device delivers the required 5mA of  
the MIDI spec, then  it's theoretically possible for the output to be  
less than 5V. Of course, the example MIDI schematics do show 5V, but  
that supply voltage is never mentioned in the text as a requirement.  
Fortunately, your circuit does provide the option of external,  
regulated voltage.

Brian Willoughby
Sound Consulting

On Dec 20, 2013, at 17:03, Dave Brown wrote:
> This is a real DIY solution but I had similar needs for filtering  
> stuff,
> transposing, etc. so I designed a small MIDI-powered processor  
> system.  The
> MIDI received stream is parsed to each of the base commands which then
> reassemble them for transmission.  You can do whatever you want to  
> the MIDI
> stream with it.  The schematics and code is public and on my site at
> http://modularsynthesis.com/processor/processor.htm
> There isn't much to the schematic if you just want a filter:  
> processor,
> crystal and caps, a couple of resistors, and a couple of diodes.   
> You can
> leave off the LED, reset circuit, and of course the switches.  I  
> have a
> variety for whatever specialty I need.  This is probably more DIY  
> than you
> are interested in.
> I use them for changing expression messages to volume messages,  
> filtering
> active sensing, transposing midi channels, keyboard splits, and  
> just messing
> around - hence the keyboard reverse.
> Dave

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