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Topic: Best programs or methods to clean up cassette tapes? (Read 16312 times) previous topic - next topic
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Best programs or methods to clean up cassette tapes?

Reply #25 –
Hi - I'm Hans van Zutphen, the developer of Tape Restore Live. I just found this thread (through my visitor logs) and I've read the story about removing wow and flutter using the high pitched tone.

Actually, at the time when I wrote Tape Restore Live I've been looking for such tones - but I suppose they are not present on normal audio cassettes. I've tried if I could find remains of the 19 kHz FM stereo pilot for FM radio recordings, but I couldn't find anything.

If such tones are present, the processing to remove wow and flutter would actually be really simple: Measure the exact frequency of the tone, and adapt the sampling rate to make the frequency of the tone constant.

I have considered looking at the recorded audio itself, but many changing frequencies are supposed to change (vibrato effects) so that would at the very least not be easy - and probably often make mistakes.

I assume that there are no such tones - even when sampling on very high frequencies - on cassette tapes?

An alternative solution that might work, although nowhere near as good as the examples with a guiding tone: If I analyze a larger portion of sound (say one minute) instead of just a very short piece of it, I could make a graph containing the measured wow and flutter of that minute, and then remove the wow and flutter frequencies that are only present sometimes. That way I would get a "description" of the type of wow and flutter that the tape contains - and then I can remove only that..........  This does assume that the wow and flutter are more or less constant and continuously present. Alternatively, if the tape recorder is still present and it still causes the same wow and flutter, it would even be possible to record a constant tone to measure the type of wow and flutter that is present. Or if a good quality recording is present, and the same recording is present on a tape that contains the wow and flutter, it would be possible to distinguish wow/flutter from vibrato effects as well, and create a profile for the tape or recorder. Which could then be used to improve recordings of which no HQ version exists.

When I have some time left I'll look into this - doing this might actually work without any bias or other guiding tones... (Although of course nowhere near as good).

Best programs or methods to clean up cassette tapes?

Reply #26 –
Quote from: Specy on
Hi - I'm Hans van Zutphen, the developer of Tape Restore Live. I just found this thread (through my visitor logs) and I've read the story about removing wow and flutter using the high pitched tone.

Actually, at the time when I wrote Tape Restore Live I've been looking for such tones - but I suppose they are not present on normal audio cassettes. I've tried if I could find remains of the 19 kHz FM stereo pilot for FM radio recordings, but I couldn't find anything.

If such tones are present, the processing to remove wow and flutter would actually be really simple: Measure the exact frequency of the tone, and adapt the sampling rate to make the frequency of the tone constant.

I have considered looking at the recorded audio itself, but many changing frequencies are supposed to change (vibrato effects) so that would at the very least not be easy - and probably often make mistakes.

I assume that there are no such tones - even when sampling on very high frequencies - on cassette tapes?

An alternative solution that might work, although nowhere near as good as the examples with a guiding tone: If I analyze a larger portion of sound (say one minute) instead of just a very short piece of it, I could make a graph containing the measured wow and flutter of that minute, and then remove the wow and flutter frequencies that are only present sometimes. That way I would get a "description" of the type of wow and flutter that the tape contains - and then I can remove only that..........  This does assume that the wow and flutter are more or less constant and continuously present. Alternatively, if the tape recorder is still present and it still causes the same wow and flutter, it would even be possible to record a constant tone to measure the type of wow and flutter that is present. Or if a good quality recording is present, and the same recording is present on a tape that contains the wow and flutter, it would be possible to distinguish wow/flutter from vibrato effects as well, and create a profile for the tape or recorder. Which could then be used to improve recordings of which no HQ version exists.

When I have some time left I'll look into this - doing this might actually work without any bias or other guiding tones... (Although of course nowhere near as good).

Hi Hans,
          If you do find time to do some work on Tape Restore Live would you consider producing a VST or Direct X plug in version? I do all my restoration work from within an audio editor and would love to be able to use it from there. I'm sure a lot of other people would find it useful too.

Best programs or methods to clean up cassette tapes?

Reply #27 –
I'd love to see this as VST or Direct X plugin too
So i could use it with audacity or nero wave editor instead of installing winamp only for this purpose.

Best programs or methods to clean up cassette tapes?

Reply #28 –
Quote from: Specy on
Hi - I'm Hans van Zutphen, the developer of Tape Restore Live. I just found this thread (through my visitor logs) and I've read the story about removing wow and flutter using the high pitched tone.

Actually, at the time when I wrote Tape Restore Live I've been looking for such tones - but I suppose they are not present on normal audio cassettes. I've tried if I could find remains of the 19 kHz FM stereo pilot for FM radio recordings, but I couldn't find anything.

If such tones are present, the processing to remove wow and flutter would actually be really simple: Measure the exact frequency of the tone, and adapt the sampling rate to make the frequency of the tone constant.

I have considered looking at the recorded audio itself, but many changing frequencies are supposed to change (vibrato effects) so that would at the very least not be easy - and probably often make mistakes.

I assume that there are no such tones - even when sampling on very high frequencies - on cassette tapes?


I'm under the impression that at least some of the work involving tracking residual HF tones due to things like bias, involved using tape heads with very narrow gaps, and/or also involved tapes recorded at high speeds like 7.5 or 15 ips.

Best programs or methods to clean up cassette tapes?

Reply #29 –
If you only need the Azimuth filter, you can use my program Stereo Tool of which there also is a VST version:
http://www.stereotool.com/

I'm very busy with other things right now, so it will take some time before I can make a VST version.

Best programs or methods to clean up cassette tapes?

Reply #30 –
Besides HF bias and FM pilot, DC hum and monitor 15.6kHZ tone are rather common artifacts that could be used to remove tape flutter. I've also seen an odd 8khz tone on a tape recoding of a FM broadcast that would seemed to fluctuate the same as overall pitch. Surely this must be a trivial to correct with frequency analysis and resampling. Anyways I made a feature request to Sox here: https://sourceforge.net/tracker/?func=detai...amp;atid=360706
 
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