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With my Yamaha CLP-150, I have tried to plug my PC with MIDI and audio-in, and found an important humming noise (as I have found with USB and audio).

I could get rid of this noise unplugging the MIDI-IN (this one is not used by a virtual piano). But it seems weird to me... I thought the advantage of MIDI was the optic isolation which prevents ground loops.

As the MIDI-IN jack of my piano should be isolated by an optocoupler inside my piano, I can't blame my MIDI-USB adpater (a M-Audio Uno MIDI interface... not one of the cheapest MIDI-USB interface). Does my (old) Yamaha present some current leakage which could explain the noise ?

Still probaly a ground loop, as most likely the midi cable has screening or ground connectors.

Try plugging your DP and computer into different outlets..Even if they are, try several others... sometimes putting them on different circuits is all it takes.

@spanishbuddha : You should be right... a quick look in my "service manual" shows me the connection of the MIDI shield of the jack directly to the ground... but also some pins to the ground through capacitors (I don't know why... and I have never seen this in MIDI schemas).

I have same issue. I notes that a year ago. Thankfully I don't really need this kind of setup (midi and line-in connected to the PC) but I find it annoying too. Was very obvious noise.

Not sure who to blame, but my guess is the motherboard fault or something on the PC. Apparently they share the ground for usb and audio jacks. They should try isolate as much as possible all audio with the rest of the computer.

What you can try is this: You know the usb connectors on the front of the computer? They are connected to the motherboard with a particular connector that is like a rectangle with holes. And you notes the mic and headphone plugs in-front of the computer? Well, generally the case manufacturers make the mistake of joining the ground of the audio ground and the USB ground in the circuit-board of the front of the case. Because of this every-time anyone plug a headphone and a flashdrive (or basically anything) on the USB front port, I can hear noise on the headphone. I solve this modding the circuit board of the front of the case, where the USB and audio plugs are solder.

I don't know if this kind of mod would solve your problem, though. But at least you can easily do a test disconnecting the audio ports of the front of the case from the motherboard, and connect the midi-usb to the front of the case. This will prevent the usb ground connect to the audio ground, at least in that point. Don't know if later they re-join somehow, but this for sure fix my problem with the headphones. Was different problem, but maybe works for you too.

Do the test and lets see...

Yes, it's annoying, however if none of the above suggestions resolve the issue, an additional piece of hardware such as the Behringer 'Hum Destroyer' should do the trick.

Cheers,
James
x

Either that or get a better interface. The m-audio is decent, but basic. My Roland Quad Capture has a ground lift on it, which I think would also solve the problem. Maybe look into interfaces that offer a ground lift option.

I was bedeviled by hum, from the computer's soundcard, in my computer + DP + mixer setup -- many wires, many wall-warts.

I finally tracked it down to a ground loop involving the printer. Unplug the printer's USB cable, and the hum disappears.

It's sometimes a matter of trying everything, until something works.

. Charles

Ha, I like that solution. On my laptop setup, nothing to do with DP 's, to solve the audio hum from connected speakers, I have to connect the printer!

Frédéric be aware that early MIDI interfaces did not use opto-isolation

Ian

As I have said, the CLP150 do have an opto-coupler.... But shunts the shield of the socket to the ground and connects some pins to the ground with capacitors.... Yamaha seems to manage to make a not-isolated MIDI-IN with a (not-usefull) optocoupler.

I had ground loop problems when connecting to other equipment. I shielded the earth connection (pin) with a piece of paper. Its fine now.