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I'm conforming and repairing a foreign language version of a classic 1941 film. Among it's many problems is an inaudible high frequency tone that screeches when I scrub. Obviously slowing makes it audible. I'm working in Pro Tools. The source is, of course, mag. You can see the high frequency saw tooth tone when you zoom in. Some mistake must have been made somewhere in the recording or transfer process. Is this bias and how did it get there? What causes this and should I try to remove it? I have iZotope I can afflict on it if the consensus thinks it should be removed. Thanks for the help!

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2 Answers

Well if it is inaudible, unless you plan on pitch shifting the audio down, it sounds like it doesnt need to be removed?

It is probably there because when it was transferred to mag, it may have transcoded frequencies from the mag above the our audible range and when you scrub, your pitching it down in varispeed which would cause it to fold down higher frequencies into the audible spectrum.

But if you do want to remove it, why not just use iZotope spectral repair and do a vertical attenuation on a 4096 window?

Not sure if that helps at all..

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Try doing a varispeed on a section of the file, slowing it down by 50%. Then run that through spectral analysis to find the pitch of the tone (or sweep it with an EQ). Then, simply notch out the actual tone (existing at 2x that frequency) from the original 100% speed. If everything's within the 48k domain you should be fine since your within the Nyquist limits that all major EQs tend to cover. If you're in the 96k domain and beyond, you may have to rely on something like iZotope to filter it out since EQ plugin's don't go beyond the frequencies excited within the 44.1/48k range, at least any of the ones I've worked with. Or, cut the speed in half, do the notch, and 'un-do' the varispeed. I'd consider that more of a last resort though since the double varispeed may have affects on the integrity of the source.

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