The Mudcat Café TM
Thread #155388   Message #3654653
Posted By: GUEST,CJB
28-Aug-14 - 03:31 PM
Thread Name: Tech: Removing hum from old tapes
Subject: Tech: Removing hum from old tapes
I have a number of off-air reel-reel recordings that I'd like to rescue by digitising them. I have digitised some of them them to WAV files. BUT they all have an amount of mains hum on them. Audacity Spectrum Analysis shows that this is around 50 KHz plus harmonics. The strongest harmonic is 200 KHz, then 100 KHz, then 50 KHz, then 400 KHz. But these are all +/- 10 KHz - it is a noisy hum.

If I use a Single Parametric effect on these frequencies in turn (at about -30db) the hum is nullified, but so is the audio!! Boosting the audio volume only brings back the hum. And the audio also sounds strange without any depth.

I have also tried notch filters - again on the above frequencies. But even being very selective with a high Q factor the result is the same - strange sounding audio.

Then I tried highlighting 0.5 sec. of noise (from a gap in the actual performance recording). Then I 'taught' Audacity what that noise represented. Then I applied the associated noise filter. But whilst the hum disappeared in the quiet parts of the recording as soon as the loud parts were played so did the hum. The hum had been filtered from the quiet parts, but not where it was embedded in the loud parts. This resulted was an audible pulsing effect.

What do folks here recommend please?