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Old February 7th, 2012, 07:47 PM   #1
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Dealing with bad tape flutter?

This is a bit off topic, as video is not involved... just audio. Still, there are a lot of experienced people in this forum, so I figure it's worth asking.

Someone wants me to try to clean up some old open-reel audiotape. It has terrible flutter. (I can't really imagine how they got this much flutter on a reel-to-reel system; it must have been a terribly cheap consumer recorder.) I've dealt with some bad archival material in the past, but nothing to match this.

There are other problems, too, like significant background hum and other noise. But of course a frequency-selective filter won't work correctly when the hum frequency is fluttering around constantly. Aside from that, the flutter sounds terrible, of course.

Has anyone heard of any sort of software that will reduce flutter? It would, I suppose, to be some hybrid version of auto-tune, but really more complex than that. Frankly, I can't imagine how such a thing would be possible. But, as I said, I figured it can't hurt to ask on this forum.

Thanks in advance to anyone who can provide any help with this one.
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Old February 7th, 2012, 09:07 PM   #2
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Re: Dealing with bad tape flutter?

Since it has a "reference clock" (the mains hum), it is possible that the speed could be "re-normalized". But it doesn't appear to be the kind of thing you could do with your average sound editing software. It would probably take a high-end application like Sequoia, or even custom software. There are several technical (mathematical) scholarly papers online on the topic of wow-reduction. Alas, it doesn't appear to be a simple plug-in and button click.
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Old February 8th, 2012, 04:14 AM   #3
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Re: Dealing with bad tape flutter?

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Has anyone heard of any sort of software that will reduce flutter?
Yes - CAPSTAN wow and flutter removal.

I saw it at the European AES Convention last year.

There is, of course, also CEDAR. They also do a bureau service if you don't want you buy the software.

John
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Old February 8th, 2012, 09:59 AM   #4
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Re: Dealing with bad tape flutter?

Richard, John, thank you both.

Richard, using hum as a "reference clock" is interesting, similar to the pilottone on the old R-R Nagras, etc. The software would have to be capable of a very fast phase comparison, since the flutter frequency is perhaps 0.5 Hz. Unfortunately, while part of the subject recording is speech (where the hum is easily audible), much of the recording is music, where it would most likely be impossible to pick out the hum frequency from the varying musical frequencies.

John, Capstan looks very interesting! Absolutely amazing!!! (It's also interesting that my search engine did not find it.) Alas at a price of ~$4,500 USD it is prohibitive for this use. It would be great for someone in the re-mastering business, if it lives up to its promise. I do wonder what it does with spoken voice, where there's no fixed pitch structure. Although, as Richard mentions, perhaps Capstan is smart enough to find the hum and use that for reference.

When I win the lottery I'll buy a CEDAR system, although I didn't realize it could also deal with flutter... I've known about only its noise removal chops.

Ah well, some things are just out of reach. Thanks again.
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Old February 8th, 2012, 02:38 PM   #5
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Re: Dealing with bad tape flutter?

In a very recent pro audio magazine, (don't recall if it was Mix or another mag) they talked of remixing the Grateful Dead's 1972 European tour album. Using the bias as a clock source from the multi-track masters minimize or eliminate wow and flutter.
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Old February 8th, 2012, 05:58 PM   #6
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Re: Dealing with bad tape flutter?

Yes, that would work if all the wow/flutter was introduced to the final generation tape.

But what if the original was an old phonograph record with an off-center hole, which had been re-recorded on tape... and then the record was lost? The tape would have a lot of wow, being an accurate recording of a phono playback with wow. Yet the tape bias frequency would be constant, so bias clocking wouldn't help at all.

Apparently Capstan is the best universal solution at this time.

--

BTW, John, I'm having a hard time finding CEDAR on the web right now.

www.cedaraudio.com is 404
www.cedar-audio.com is 404
www.cedar-audio.co.uk is 404

I found an independent pre-review stating that "Respeed" will become available in Q2 2011, but I can't find anything more recent. {grumble}
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Old February 9th, 2012, 01:45 AM   #7
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Re: Dealing with bad tape flutter?

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When I win the lottery I'll buy a CEDAR system, although I didn't realize it could also deal with flutter... I've known about only its noise removal chops.
But, as I said, CEDAR do a bureau service. You send them the file and they will sort it for you - you don't have tou purchase the software at all.

Give them a ring - I posted the link in my earlier post.
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Old February 9th, 2012, 01:47 AM   #8
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Re: Dealing with bad tape flutter?

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John, I'm having a hard time finding CEDAR on the web right now.
I posted the direct link in my earlier post - it's HERE - and it works perfectly for me.
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Old February 9th, 2012, 11:34 AM   #9
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Re: Dealing with bad tape flutter?

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Originally Posted by John Willett View Post
I posted the direct link in my earlier post - it's HERE - and it works perfectly for me.
John, I clicked you link yesterday and it was dead (as were the others I listed). Indeed, it's working fine today. Thanks.
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