Awful knocking sound to get rid of

[ginlane]

Hi there,
I’m restoring an old audio that was originally on cassette tape. So, all the way through the recording it has a knocking sound, …..as if the central spindle or some other part of the cassette was knocking together during the original recording. There is a repeated rhythmic kind of knock every second or two, it’s really obvious throughout the recording. The audio is of a female choir concert given about 20 years ago. I have added a small sample audio with this post to give you an idea of my problem. I took the sample audio from a portion of the recording where there is just someone speaking, where the knocking is more clear to give you some idea of what the problem is. Of course I want to get rid of that knocking and I would be very glad if someone could tell me how to minimise it or remove it entirely using Audacity, or any other software for that matter.

Kind regards Richard Milner

[steve]

Do you still have the original recording before effects were used? If so, please post a short sample of that in WAV or FLAC format.
I'm doubtful how much can be done to reduce the knocking, but we have a better chance with the pre-effects recording.

[ginlane]

Hi Steve,

How to you know that effects were used? Actually you are correct I have and unfortunately I no longer have the pre effects audio

Kind Regards Rich

[Trebor]

... how to minimise it or remove it entirely using Audacity, or any other software for that matter ...

A thing called Spleeter uses Artificial intelligence to automatically separate sounds.
It can separate vocals from percussion, (it should interpret knocking as percussion).
Even IF it is successful there will probably be holes in the vocal where the knocks were.