A mixed mono track with 2 different RMS sources


I’ve digitalized an old compact cassette.
The original source of this tape is radio in mono and I’ve made a stereo file on a good player.

As if it was recorded on a cheap radio-cassette player with a used tape in recording and playing (the heads were probably not often cleaned), the tracking of the recording head differed quite a lot in the left and rigth channels.

I’ve used different filters available on Audacity like Channel mixer or Repair channel.
The right channel is the better on both side of the cassette.
I always had to have a look at the vu meter to see when the signal was dropping.
The result is not too bad, but I couldn’t really correct the whole sound as I wished as there are sometimes constant small signal drops in both channels.

I thought invert filter could do something in it but I don’t really understand how to use these two tracks as if if was layers.

How can I use the these two tracks after a normalization to get an optimized single mono track from the left and right channels ?

Thanks a lot for your replies.

A common cause for that on old tapes is that the magnetic surface of the tape is starting to break down and come off the tape (that’s the brown dust that builds up in old cassette players). Slight dips in volume can sometimes be improved using the envelope tool (https://manual.audacityteam.org/man/envelope_tool.html), but if too much of the surface has come off then it is not repairable other than by copying a similar bit of audio over the top of the “gap”, or cutting the bad bit out in musical fashion.

Probably the most useful tools for this type of job are “Channel Mixer” and “Repair Channel”, both of which you have already found.

Thank you Steve.

I knew that dirt could damage tape surface.
Let me show you this video : https://www.youtube.com/watch?v=cvFArqPyoyk

This is for removing vocal but the process can have an intrest.

If inversion of one channel can remove the vocal who is generally on the center, then why not create a mono file from the stereo one (the thing I want to do), copy and layer one of the stereo track (L or R), apply invert on it, then make again a mono with it.

I tried this and there is an idea in it if I make another layer with one of the stereo track. I make this again with the other channel. Then I’ll have 4 channels.

Invert on one channel always remove (or cancel) the sound in the center.

Your tapes may be suffering from “sticky shed syndrome” https://en.wikipedia.org/wiki/Sticky-shed_syndrome

If that is the case baking the tapes at low temperature (see the Wikipedia article) may bring improvement.

I assume you have inspected the heads on your playback deck… You will need to clean them frequently when playing old tapes.