MIDI via microphone cable ??

DeadPoet

DeadPoet

carpe diem
Hi

for what I know from it the MIDI cable only uses 3 pins, so would it be possible to for instance make a midi-to-xlr adaptor for studio-wall-connector use ??? Or would I run into cable resistance problems or so ????


Any help appreciated



Herwig
 
In theory you could run into impedance problems and such, yes, and the bps rate of MIDI is rather high so you do need good cables. However I'd be surprised if it didn't work, and making cables shouldn't cost you many bucks, so give it try!

Don't connect it to a mic of a preamp, though, I don't think the mic would like midi signals, and I don't think a midi interface would like +40V :)
 
I agree with regebro that it should be possible, but I think it’s a really bad idea. Using different connectors for different things helps prevent all sorts of miswiring accidents.

If you’re trying to run wires in the wall then what about this:
Put two of those blue PVC boxes in the wall. Run some midi wire between the two. Get two blank wall plates with the screw holes spaced so that they fit over a box. Buy 2 midi / keyboard female connectors from radio shack (like the type of connectors on the back of a keyboard). Drill a hole in the center of the wall plate for the midi connector and 2 small holes to bolt the connector to the wall plate. Solder the connecters to the wire. Assemble.

Urea wall plates are stronger than nylon, use urea.
 
thanks for the replies. It was just an idea to seehow flexible a wall plate full of LR in a studio could be ;)
(could benice to be able to MIDI-record a triggered drum kit as well as with microphones)

Gonna hafta reserve two places for a midi connector then.


Herwig
 
Yeah, that's definitely a much better idea. I thought you were in a place where the wiring was done. :)
 
Lighting equipment uses a protocol called DMX that is a digital comunication very similar to MIDI. They use special XLR cables called DMX (duh). I imagine using those cables you would be okay.
 
Hmmm..

I thought a DMX cable was identical to a microphone cable, for convenience... I'll ask the light tech of the musical I'm playing this afternoon..


Herwig
 
Almost ANY mic cable will pass audio satisfactorily - but when you start transmitting MIDI, you're dealing with a SQUARE wave, which takes TEN TIMES the bandwidth to properly transmit as its highest frequency - otherwise, leading and trailing edges of the pulses get rounded off. When this reaches a point where the slope of the rising and falling edges of MIDI pulses aren't steep enough to reliably trigger the pulse input of your MIDI device, you get errors. At that point, what you send is NOT what you recieve.

Decent MIDI cables are built with very low capacitance cable, so that the inter-electrode capacitance of the wire doesn't round off the edges of the MIDI pulses. Normal mic cable, since it is expected to be used as a low impedance transmission line, doesn't pay as close attention to cable capacitance and is typically around 30 to 75 picofarads per foot. MIDI cable, as is 110 ohm DIGITAL (AES) cable, typically has below 12 picofarads per foot, and sometimes as low as 7 or 8.

This makes a HUGE difference in how far you can run these cables before the capacitance takes its toll on pulse shape. A commercially made MIDI cable can go about 20 feet before you're asking for problems, so if you use a mic cable with 7 times the capacitance, you will probably get about 3 feet before you encounter the same problems.

If DMX uses special XLR cables for their lighting protocol, they most likely are using low capacitance cable. If you used such a cable for audio, assuming it's shielded, the only possible difference you might hear is an increase in treble response since most balanced line connectors on gear today are NOT low impedance, just balanced. (maybe)

So, your idea of using XLR cables for MIDI might work IF, and I mean IF, the DMX cables are really low capacitance and you use only that type cable. But the most sensible thing to do, as brought up earlier, is to get MIDI connectors and the CORRECT cable and wire it up to avoid confusion.

Hope all that made some sense - cable ain't always cable... Steve
 
OK, so assuming you're being a cheapskate then, can you get away with routing MIDI through an audio patchbay?

I'm thinking: Behringer Ultrapatch (like I said, cheap) and then wiring it so the current loop pair goes to the jack tip and sleeve.

Or is it that just insane?

Yes, a dedicated patchbay marked "MIDI ONLY" to prevent accidents ...

Is the Ultrapatch "isolated" so that the sleeve isn't bonded to earth, but just connects through the switching? Or is every sleeve joined to a common earth (which would stuff the idea anyway!)

I know proper MIDI ones with routing control exist ... I'm just not fussed enough yet to get one :)

Mike.
 
mjbee said:
OK, so assuming you're being a cheapskate then, can you get away with routing MIDI through an audio patchbay?

I'm thinking: Behringer Ultrapatch (like I said, cheap) and then wiring it so the current loop pair goes to the jack tip and sleeve.

Or is it that just insane?
Click to expand...

Nono, it's current loops, you can't ground one of those pins, is could seriously damage something.

You could probably do it with a balanced patchbay though, although I'm quite sure it's a bad idea. It's definitely a bad idea to mix audio and midi in the same patchbay, you'll probably end up with some serious bleed-through.

There are two types of MID patchbays: smart and stupid. The smart ones understand the MIDI-data and can route in in more or less complex ways. Very practical of course, but induces a slight delay, and you have to program them.

Second hand: Akai ME30PmkII
New: Emagic AMT8

Then there is the type that only does an electrical connection, and you patch it with standard trs cables. You can't do any advanced stuff like routing two MIDI channels to different outputs, and you can't do MIDI merge. There is no delay, though, and they use small buffers on all outputs meaning that you can use them as MIDI splitters. Pretty cheap too, and 145 punds or so, I think. ($220?)

New: http://www.dacs-audio.co.uk/midipb_main.htm
 
regebro said:
Nono, it's current loops, you can't ground one of those pins, is could seriously damage something.
Click to expand...

I know it's a current loop, who said anything about aiming to ground it? Just because the body of the jack is normally a ground doesn't mean it has to be! I was hoping to use tip and sleeve as the 2 parts of the current loop, subject to Behringer having done the earthing appropriately.

What I'm asking is :

Is the Ultrapatch designed so that the "bodies" all just tie together (or to the case), and only the "tip" is switched, or

Is the switching also applied to the "bodies". The answer to that will vary across brands of patchbay, I guess, so it would need to be checked on an actual ultrapatch.

You could probably do it with a balanced patchbay though,
Click to expand...

Yes, being 2 conductors + a ground, the 2 conductors would have to switch as a pair. That'd go. The ultrapatch is not balanced though, right?

On the link :-

10 MIDI devices in 1U -- Seems like they've taken a basic unbal patchbay, added current loop->TTL, switched the TTL over the patchbay, and reconverted. Hence being more than the 40 quid Ultrapatch :) But worth a look. Thanks!

Mike.
 
mjbee said:
I know it's a current loop, who said anything about aiming to ground it? Just because the body of the jack is normally a ground doesn't mean it has to be!
Click to expand...

No, but it should be.

I was hoping to use tip and sleeve as the 2 parts of the current loop, subject to Behringer having done the earthing appropriately.
Click to expand...

Well, It's Behringer, they'll do it the cheap way. So you can safely assume that they only switch the signal, and not the ground. Besides, I'm pretty sure almost any unbalanced patchbay would do it like this, not only because of cost, but becuase you get much less grounding errors that way.
And it doesn't sound like a good idea not to include the grounding in a MIDI connection. You'd probably end up with current loops you didn't intend, and shaky MIDI as a result.

Yes, being 2 conductors + a ground, the 2 conductors would have to switch as a pair. That'd go. The ultrapatch is not balanced though, right?
Click to expand...

Nope.

10 MIDI devices in 1U -- Seems like they've taken a basic unbal patchbay, added current loop->TTL, switched the TTL over the patchbay, and reconverted. Hence being more than the 40 quid Ultrapatch :)
Click to expand...

I think that is probably a very accurate description. :) ONe thing worth mentioning is that it, as far as I know, doesn't have a proper box. That means that you really MUST rack mount it, so you need a rack. That's the main reason I haven't bought one yet. :)
 
regebro said:
ONe thing worth mentioning is that it, as far as I know, doesn't have a proper box. That means that you really MUST rack mount it, so you need a rack. That's the main reason I haven't bought one yet. :)
Click to expand...

Er, what, like the guts are hanging out exposed? That didn't show up in the pictures! So what do you get beside a front and rear panel (and a PCB with the guts on)?

Oh well, I'm heading ever nearer to needing a rack anyway :(

Mike.
 
Well, that's how it looked on another picture of it that I saw. It's quite common for patch panels to be like that. You don't really need the rest of the stuff if it's going to be in a rack anyway.

And I wouldn't call it 'hanging out', but it's exposed, yes.
 
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