I have a number of external modules and they all work fine except for my Prophecy. When I use the Prophecy I get an audible crackle/zipper noise/data noise. The Prophecy is the master keyboard in the system and it is set to "local off". The MIDI Out goes to an input on my MIDIMan and the MIDI In is fed through two modules from the same interface. The MIDI Thru goes to the first of the same two modules in the chain. When using the Prophecy I get an audible click when I press a key and when using any of the CCs I get a lot of noise. Is this a ground loop? I thought that MIDI devices were isolated from each other via the MIDI port, so I'm not sure what causes it. All my other modules are fine, it is just the Prophecy, which is the only one which has In, Out and Thru connected. I am going to try and re-cable it, but any ideas as to why it happens?

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Midi is (supposed to be) opto isolated, but if the cable has been made up with the screen connected to the shell of the din plug it can sometimes defeat the isolation by providing a ground path independent of the midi loop through the screen.

This only shows up when the gear at both ends bonds the screen connection of the midi connector to ground, and at least one end has a pin one 'issue'.

The cure is easy, open up the connector and isolate the screen at one end.

There are of course other ways digital noise can make it into the audio, but my bet is midi cable made up incorrectly.

Regards, Dan.

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Audiophiles use phono leads because they are unbalanced people!

Yes, this was my first thought as well - MIDI opto isolation is designed to avoid ground loops, but cheap MIDI cables are sometimes incorrectly wired.

It’s also possible that sensitive audio cables (such as those connected to mics) may pick up interference from nearby MIDI cables, so keep them a reasonable distance apart.


Martin

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YewTreeMagic

Ah! DINs. Super things!

Dan. "Pin one problem"? I know what you mean but you are going to confuse the noobs! Pin TWO has ever been the common pin for common DIN connectors.

Then, cutting the common pin 2 connection is not that easy for the beginner (practice on XLRs!). For one thing the plugs are often moulded these day. Then even if he gets it apart without breaking any vital wires (pins 4&5) he might never get it back together again. Gaining access to pin 2 can also be difficult. Two solutions..
1)Use a craft knife and carefully split 25mm of the outer sheath about 25mm back from a plug. Now unpick the shield until you have open circuited it completely (check with a multimeter. Don't even THINK of doing this sort of thing without one!). Tape it all up for mechanical support.
2) Buy two 5pin DIN chassis sockets from Maps and just wire 4 and 5 pin for pin with about 50mm of wire. Tape up, heatshrink or if you are especially handy, fit into a 25mm section of plastic tube. The small section of unshielded wire will do no harm. You will of course need another DIN lead.

Dave.

Thanks for the responses gentlemen. I also suspected the cable, so I'm going to note down the current cabling configuration, strip it all out and re-cable, starting with the Prophecy. It is quite frustrating, because the Prophecy can really perform well, if you use the CCs well, but in this case it is all ruined by the zipper noise. I'll report back when I have had the chance to jig it around.

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Well I tested a few different leads and found that all my MIDI leads have five pins connected. I took one of the leads which didn't have a moulded end and snipped through pins 1, 2 and 3 leaving just the important pins 4 and 5 connected at one end, but alas the buzz is still there.

Next step is to try it in a different cabling order and set up, but that can wait for another day.

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Quote Richie Royale:

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Well I tested a few different leads and found that all my MIDI leads have five pins connected.

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Then they are not really MIDI leads

Seriously, a lot of problems over the years have been due to unscrupulous companies passing off 5-pin DIN to 5-pin DIN cables as suitable for MIDI


Martin

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YewTreeMagic

I know! But they all work without any problems, except the Prophecy connection.

I almost bought some new cables to sync my x0x, only to realise I already had 5 pin wired DINS!

I'm going to try the Prophecy on a single output and input and see if that does anything to resolve the problem. I have some MIDI ports on my audio interface as an alternative.

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yeah, MIDI cables are basically supposed to be balanced microphone cable (i.e. a screened twisted pair) but with a DIN plug on the end instead of an XLR.
(And the legendary Octave-Plateau Voyetra 8 synth actually had XLR MIDI sockets, fact fans!)

If I recall correctly, the MIDI committee originally intended that people *could* just use microphone cables for MIDI cables...cos that would be really simple and microphone cables were already ubiquitous and available - and also ideally suited, cos the twisted pair with braided screen would be good for stopping the 32 kbaud digital signal spewing everywhere...

... but someone on the committee (dunno who? the delegate from Planet Stoopid, perhaps?) insisted that musicians would be too dumb to cope with this, and would keep plugging microphones into MIDI sockets then ringing up Roland to ask why their synth wasn't responding to voice control. Or something.
So an engineering compromise was reached, whereby MIDI cables were mic cables with DIN plugs stuck on the end.

Have I got that right? (All a bit before my time! In 1983 the only cable I was using was to connect my ZX Spectrum to the telly and the 'ear' and 'mic' lead for the cassette recorder!)

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~~~ A weasel hath not such a deal of spleen as you are tossed with! www.feline1.co.uk ~~~

I knew that there were XLR MIDI cables but I am of the opinion that it WAS a stupid idea! Almost as bad as XLR3s as speaker outs on some old heavy duty PAs!
Mind you the 180drg "audio" DIN was not much wiser, why not the much rarer 240dgr jobbie? I have used standard DIN leads in my very modest system without problems and even some VERY old DIN puter keyboard leads from the cheapo bin at Maplins. Note however that you can run foul of a "crossed" DIN lead that was made to enable old tape machines to dub sound tape to tape.

And sorry to bring it up again(!) but FTP patch cable makes excellent MIDI leads and if you can find some 2 pair shielded Belden 9534 it is loverly stuff!

Dave.

Quote ef37a:

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I knew that there were XLR MIDI cables but I am of the opinion that it WAS a stupid idea!

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Why? (he asked curiously...)

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~~~ A weasel hath not such a deal of spleen as you are tossed with! www.feline1.co.uk ~~~

Quote feline1:

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Quote ef37a:

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I knew that there were XLR MIDI cables but I am of the opinion that it WAS a stupid idea!

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Why? (he asked curiously...)

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Because although I do not know what the consequences would be of plugging a MIDI source into a mic input or connecting it to a venerable 4038 I would not want to try it! This is not about people being stupid, *it just'appen. I can recall theatres where the sound system (100Vline) was on 3pin 2amp mains plugs!

In any case, when I started my interest in audio, equipment, especially mics had all sorts of proprietory connectors, differentiating MIDI conns' from all others would have been no economic hardship. Then, compared to mic/line cables, MIDI leads are very short and mostly fixed site so they do not need to be quite as rugged.
I am no lover of the DIN! Made too many variants up for that but a decent, metal 240dgr with only 2 or 3 wires in it is not that bad to build.

Dave.

MIDI signals are just itty-bitty TTL level things, are they not? Wouldn't hurt a fly. Nor a phantom powered mic...?

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~~~ A weasel hath not such a deal of spleen as you are tossed with! www.feline1.co.uk ~~~

I've been using mic cable to make MIDI leads for 20 years. Never had any trouble at all. Except with forgetting to pop the plug bodies over before soldering... Maplins no-brand cheapo stuff does well enough, and is nicely flexible, which helps. Neutrik DIN plugs are not so expensive, so making your own custom-length MIDI leads is something I'd recommend. I've got several of just a few inches each for hopping between adjacent units - much tidier than cable-ties around the ubiquitous 3-metre jobs.

Back on topic,
when you opened up the plug, did you see if the cable screen was connected to the metal shell in the connector? That connection is the one most likely to be screwing you over.

MIDI is a 20mA current loop, usually driven from a 5V rail with a transistor and a few hundred ohms of series resistor, input is typically a 6N137 opto isolator IIRC, typically again with series resistance and maybe a transorb or so for protection.
With good quality twisted pair cable, it really does not need a screen connection all that much, but people seem to use screened lines anyway.
Given its opto isolated inputs, I would not expect P48 up it to be a problem, but I could maybe see the output side getting a little upset with that, particularly is plugged in while the phantom was up (so the input coupling caps discharge into the midi driver).
XLR would have been a MUCH better choice then fecking din plugs, and could even have been sexed to make getting the right wire in the right hole in the dark a bit easier.

For all that, midi, a bit like DMX512, is evidently good enough that no replacement is going to gain any serious traction.

Regards, Dan.

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Audiophiles use phono leads because they are unbalanced people!

Ok Dan!
XLR4s then! "We" used to use them for 100V lines and DC300As.

Good cheap solution today would be RJ45,unlike a DIN they will stand for a size 13 once or twice!

Dave.

Quote dmills:

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With good quality twisted pair cable, it really does not need a screen connection all that much, but people seem to use screened lines anyway.

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Graham Hinton's site http://www.hinton-instruments.co.uk/reference/midi/promidi/pg02.htm
says "In general, any good quality microphone or data cable may be used, but it should be noted that the MIDI specification was drawn up over a decade before current EMC legislation was introduced. MIDI was designed to work well within a typical studio installation without introducing digital breakthrough or ground hum loops, but it was not designed with radio frequency interference in mind. As nearly all MIDI equipment contains microprocessors with clock frequencies above 1 MHz all connected cables have the potential to act as aerials regardless of the equipment meeting any regulations or not. This is because the equipment was only tested in a "typical" situation and if the manufacturer does not supply the cabling it does not have to be tested with cables attached.

Cables with "lapped" or "helical" screens should be avoided if possible as they have poor screening properties above the audio bandwidth. They may also cut through the insulation if flexed a lot or if stored knotted up. Use a braided screen cable for equipment connections and foil screened twin pairs for permanent installations. Ideally a foil screen with overall braid should be used, but these are quite hard to source. As no DIN connector used for MIDI is ever going to be suitable for RF screening this is always going to be a compromise."

However the only foil + braid cables I ever found for sale were by 'Planet Waves', and they had all 5 pins connected /sighs/

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~~~ A weasel hath not such a deal of spleen as you are tossed with! www.feline1.co.uk ~~~

Well the opto isolation should mean that with even mostly sane layout there is little opportunity for radiated emissions issues from the gear at the receiving end, and the transmitter really should not be generating edges that are all that fast anyway.

Certainly the few hundred ohms from the +5V rail with the transistor switching the other leg to ground via another hundred ohms or so is not exactly going to produce fast edges, I would be very surprised if conducted (never mind radiated) emissions were an issue via that route for anything even mostly sane.

In reality, any old mic cable will do just fine for midi, and the biggest issue is finding din plugs that do not totally suck.

Regards, Dan.

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Audiophiles use phono leads because they are unbalanced people!

Nowt wrong with the RF stopping for a decent DIN plug Feline?

I agree the plastic abortions leave about 10mm unshielded but I am now looking at an all metal RS type that must be all of 40 years old!

BTW, that Belden cable is foil screened with drain wire.

Dave.

Quote dmills:

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Well the opto isolation should mean that with even mostly sane layout there is little opportunity for radiated emissions issues from the gear at the receiving end, and the transmitter really should not be generating edges that are all that fast anyway.

Certainly the few hundred ohms from the +5V rail with the transistor switching the other leg to ground via another hundred ohms or so is not exactly going to produce fast edges, I would be very surprised if conducted (never mind radiated) emissions were an issue via that route for anything even mostly sane.

In reality, any old mic cable will do just fine for midi, and the biggest issue is finding din plugs that do not totally suck.

Regards, Dan.

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http://www.google.co.uk/products/catalog?hl=en&cp=19&gs_id=1k& xhr=t&q=all+metal+din+plugs&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&wrapid=tljp 1334967797234036&um=1&ie=UTF-8&tbm=shop&cid=7409744154573526395&sa=X&a mp;ei=G_6RT6PnGM-s8QP8sdjODA&sqi=2&ved=0CHwQ8wIwAw#
Bazinga!

Edited by ef37a (21/04/12 12:26 AM)

Why do things NEVER work here the way they do everywhere else????

Dave. Anyhoo Neutriks do good ones.

Slight hijack...

After all that talk about what constitutes a "proper" MIDI lead, does anybody have any suggestions where to get "proper" MIDI leads at reasonable (=low) cost?

Quote BillB:

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Slight hijack...

After all that talk about what constitutes a "proper" MIDI lead, does anybody have any suggestions where to get "proper" MIDI leads at reasonable (=low) cost?

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http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/646790.xml Only plastic plugs I fear but cheap enough to buy spares.
I fear if you want rugged mic cable and metal plugs you wil have to roll your own?

Dave.

Quote ef37a:

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Quote BillB:

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Slight hijack...

After all that talk about what constitutes a "proper" MIDI lead, does anybody have any suggestions where to get "proper" MIDI leads at reasonable (=low) cost?

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http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/646790.xml Only plastic plugs I fear but cheap enough to buy spares.
I fear if you want rugged mic cable and metal plugs you wil have to roll your own?

Dave.

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So are these "5-pin DIN Stage leads" wired only pins 4 and 5 as discussed above?

Quote BillB:

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Quote ef37a:

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Quote BillB:

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Slight hijack...

After all that talk about what constitutes a "proper" MIDI lead, does anybody have any suggestions where to get "proper" MIDI leads at reasonable (=low) cost?

---

http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/646790.xml Only plastic plugs I fear but cheap enough to buy spares.
I fear if you want rugged mic cable and metal plugs you wil have to roll your own?

Dave.

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So are these "5-pin DIN Stage leads" wired only pins 4 and 5 as discussed above?

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I couldn't say but in any case pins 1 and 3 should not be wired on a standard MIDI socket so I do not see that it matters?
I said before that I had never had a problem with fully wired DINS for MIDI and I have never read of anyone having a problem either.

Dave.

The issue is less pin 1 & 3 as it is the metal surround and the screen connection....

Regards, Dan.

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Audiophiles use phono leads because they are unbalanced people!

Quote dmills:

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Back on topic,
when you opened up the plug, did you see if the cable screen was connected to the metal shell in the connector? That connection is the one most likely to be screwing you over.

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Hi Dan,

no the shield was connected to pin 2 and even had a small amount of heat-shrink on it. I've not had a chance to re-cable yet, going to make some music this week instead of spending time chasing this problem for the moment.

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