How to fix hum

This recording was setup with three lapel microphones on stage, recorded into a desk. The hum is terrible. I have tried the following nyquist prompt: (do ((i 1 (+ 2 i)))
((>= (* i 60) (/ sound-srate 3)) s)
(setf s (notch2 s (* 60.0 i) (* 8.0 i))))

I have also tried going through tiny sections and fixing it via noise reduction, but no luck. Is it completely stuffed?
Screen Shot 2019-04-09 at 11.27.01 am.png
Link to sample:

If you use Plot Spectrum (, you can see that the hum is at 206 Hz.

The “Notch Filter” ( can mostly fix this (note that a bit of hum will remain for the first half second or so).

Suggested settings for Notch filter:
Frequency: 206
Q: 10

The result:

Better, would be to work out where that 206 Hz tone is coming from, and prevent the problem from happening.

The hum is terrible.

There is no powerline hum. That sounds like ventilation fan to me. By the time you get to “terrible,” that kills most if not all of the post production fixes. Stiff patch application damages the show.

Is that tone audible at the mixing desk? Does the mixing desk have a built-in microphone and it it selected? You may be listening to the desk vent system.

Is this an on-going production? Get a long microphone cable, disconnect two of the microphones and walk the remainder around the studio announcing as you go. Some of this is a human problem. If we spend enough time in an environment, we “tune out” the resident noises and just don’t hear them. They stay tuned out until you introduce a recorder and change the environment. You get the recording home and “Good Night! Where did that tone come from?”

206Hz is not a standard power frequency, so we’re immediately reduced to computer fan noise or other computer related devices or equipment. Did one of the performers have a laptop?

Describe the environment, chairs, type of microphone, etc. etc.


Do you see that haystack right around 9000Hz? That’s probably Essing where all your SS sounds are piercing, loud and gritty. Many home microphones do that because it sounds “crisp and professional” (it says here). It hurts my ears and there is a recommendation from the audiobook publishers that you not use a microphone which does that.

There are two DeEssers available, but they’re difficult to adjust and use.