Noise infecting audio cables, part 3 of 3 (for now)

So here’s the latest story (it’s a pretty long one).

This summer I decided to do some refurnishing in the studio. And with that came the opportunity, well it was pretty much a must, to change how the cables where running.

I dissconnected almost every cable and made sure audiocables, usb-cables and power cables were separated from eachother. In fact even midi-cables were somewhat separated.
None of these types ran alongside eachother anymore.

And even though all the gear was connected to only one grounded outlet I made sure they where all connected to only one single output on the “clean power surge protector”-thingy.

This did help with some of the hum. But let’s see what happened and what was the problem.

I had two problems. First I had a problem with to loud hum, a 50 or 60 Hz signal usually caused by a ground loop. Then I had a problem with a higher sound, a squeal or squeak for no better explanation, that was definitely disturbing some of the equipment.

I isolated the ground to one of the affected synthesizers and the squeaky sound disappeared. This sound was present in some synthesizers when powered off and in some only when the synthesizer was powered on.

And isolating ground is not a good thing (even illegal here).

The changes I did (described previously) did help with lowering the hum and also the squeak but did not solve the latter to a satisfactory degree. I had to search on.

I did connect and disconnect all equipment one by one, a 150+ cables, and it was a pain.

Finally I tracked the squek down! It was one of the powered USB.hubs (I know I know, I did write this before) running a USB-cable into my motif es rack and from there distributing the squeal via ground to all other equipment.
Remember I use optical ADAT connections from my studio into my computer so I wouldn’t have deal with this kind of things. But much is connected by USB today for easier integration with the DAW.

So I wiggled the USB-hub a bit and noticed the sound changed. Strange. When I disconnected it’s own power the squeal went away! So some circuit in there was spreading this pollution into my system. I have another identical hub that doesn’t have this problem.

So now the noise pollution is finally down to acceptable semi-pro levels. You cannot hear it at a normal studio listening level. And since all digitally connected eqipment isn’t affected by it, it is now solved.

So there, now you have a couple of things to check.
A short list:

  • Faulty cables, these are hard to detect and most often the culprit
  • Connectors not inserted correctly or all the way.
  • Power cables not connected correctly or at different outlets
  • Power cables and audio cables running alongside.
  • Through USB-cables or circuits in the USB hubs

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