Having connected up my new XS rack to the mixer I was impressed by the low noise and high quality sound of the analogue outputs.

After connecting a USB cable to get started with the editor, I noticed a subtle mains hum – not too intrusive, but it was there, nevertheless.

Just to investigate, I tried a different USB cable, running it around the front of the computer to save scrabbling about behind. Hum cured! Excellent – I’d solved the problem….

However, as soon as I fed the new cable back behind the computer for everyday use, the hum returned.

A bit of closer investigation revealed that the cable was lying close to an external power supply and was clearly picking up the hum from that.

Re-routing the cable away from the PSU removed the hum from the signal chain entirely.

Just a cautionary tale that might possibly help others trace any mystery “hums”.