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"This buzz is an annoyance for sound engineers trying to make the highest quality recordings."

It hit me a while back when I was writing the software for a test stand for a hearing aid as a summer intern. Mysterious 60/120/180 Hz frequencies appeared on our analysis, soon to be discovered as the motors for the building's ventilation unit. It was barely noticeable to anyone, but it was quite obvious to our test equipment, even in an insulated box.

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It may be that the reason was not the sound of the motors, but the effect of the motors on your electricity supply for the audio gear. Isolating the electricity (running stuff from batteries) might give more benefit than the audio insulation of that box.

Not just audible, either. Electric motors are very naughty when it comes to interference, as are ballasts in light fixtures. I've seen a street light throw off enough interference to disconnect a poor guy's DSL every day when it turned on, and it was only after repeated troubleshooting and hassle that an eagle-eyed install tech noticed (by waiting with the customer at the right time). It's a legend within that company now.

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