How to clear up audio beyond Noise Reduction?

[Kilm]

Hi folks,

I'm trying to tidy up the audio on some old documentaries from the 70's. I've sorted out the Db level and Noise Reduced a lot of mess off of them, but there's a fine high pitched (to my ears anyway!) bit of noise that I can't get shot of.

It's not even visible until you drop down right into milliseconds. I've attached how it looks for reference.

Question is - do I just live with it, or is there something more that can be done? I've tried Noise Reduction and Click Removal, but my skills with Audacity are limited and so I've had no success.

The noise is exceptionally noticeable in some parts of silence, of which there's a fair bit as it shows footage, etc.

Any advice greatly appreciated.

Thanks!

noise.png (92.57 KiB) Viewed 384 times

[Trebor]

but there's a fine high pitched (to my ears anyway!) bit of noise that I can't get shot of.

Zoom-in on the vertical-scale to see very quiet parts of the waveform.

The noise is exceptionally noticeable in some parts of silence...

A noise gate is a possible solution: it is designed to reduce/remove noise in what should be silence.
https://en.wikipedia.org/wiki/Noise_gate
http://wiki.audacityteam.org/wiki/Nyqui ... Noise_Gate

If the noise is a constant-pitch whistle/whine, then notch filter(s) may be a solution.
https://manual.audacityteam.org/man/spe ... ml#example