[LAD] [semi-OT] midi snakes using CAT5?

Dan Mills dmills at exponent.myzen.co.uk
Sun Nov 1 17:55:44 UTC 2009

On Sun, 2009-11-01 at 12:56 -0400, Raymond Martin wrote:
> 15 meters is a recommendation based on typical cables used in a simple system.
> Data corruption ensues somewhere after 15m, depending on cable quality, EMI,
> and so forth. I would imagine a CAT5 as having better shielding and IIRC runs 
> for that are advised to somewhere up to 50m. Different frequency ranges though,
> so signal loss/degradation per meter may vary.

My recollection is that when MIDI was originally standardised, they
needed to specify a maximum length, and that 15M was chosen somewhat
arbitrarily (No tests were done, no eye patterns examined). 

Now midi is actually at heart a 5mA current loop interface running at a
fairly low baud rate (31.25 Kbaud IIRC), so should be good for far more
then 15m without any problem, however nobody really knows and it will
depend a bit on the environment and the receiver. 

Interference is unlikely to be an issue assuming good quality twisted
pair cable (Cat 5 counts), but bulk capacitance just might ultimately
limit the length. 

Regards, Dan.

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