Is it best to use notch filter in spots or entire audio?

Working on an audio book - read your detailed info on how to use notch filter to remove background hum. Very helpful! In an hour-long audio, I hear a background hum in several spots. Do I use the Notch Filter effect just in those spots or can I apply it to the entire audio and it will fix all the spots at once?

remove background hum.

You should remove the background hum before you record. It’s nice to think you can solve performance problems by applying filters and effects, but they all affect the quality of the voice and are to be avoided.

It’s a danger sign when someone goes into a project planning on rescuing it from known damage.

I hear a background hum in several spots.

That’s aother danger sign. Hum should be there all the time, not come and go. There’s a very common problem where home recording microphones try to help you by automatically adjusting the quality of the work. Windows settings, Chat and Skype can all do this. Make sure Skype and Chat are turned off and not waiting in the background.

Can you tell where the hum is coming from? There’s a trick you can try. Drag-select some of the hum on the timeline and make it louder (Effect > Amplify). Sometimes that can trigger a recognition of what it is.

“Oh, right. That sounds like my refrigerator.”

It’s good to have WAV backups of any live, unprocessed readings so you don’t damage anything by accident. File > Export: WAV (Microsoft) 16-bit. You should never have to read anything again because the computer or Audacity dumped in the middle of an edit. Also remember we can’t take effects or filters out of a performance later and Audacity Projects do not save UNDO.

Equipment problems? Does it change when you touch the microphone?

If you have a directional microphone, you might be able to aim it around the room and find what’s causing the noise. That’s how I finally found a low volume humming bass cabinet in my music performance system. I solved that one by unplugging the cabinet from the wall. No more hum.


Steve’s de-hum plugin has a threshold setting : it only kicks-in when the volume is below threshold,
(hum is more noticeable then),

Thanks so much - these answers were great - very helpful. I will try these tips!