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Topic: Take the best out of 2 noisy tapes (Read 5295 times) previous topic - next topic
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Take the best out of 2 noisy tapes

Hi there,

Say I have 2 exactly the same tapes, both with some noise etc.
If I record them both to some lossless format, is there software that can take the best of both tapes?

I mean is there some software that can "overlay" the 2 recordings and make the best out of it by analyzing the noise and artifacts in the recordings and for every moment take the one from the tape that has the best quality for that moment. This would then result in 1 digital version that has the least amount of noise and artifacts that could be made from the 2 (or 3, 4, 5) tapes.

Thanks,
Stan

Take the best out of 2 noisy tapes

Reply #1 –
Assuming you can align them (which may not be trivial), you could average the two which would reduce your noise.

Take the best out of 2 noisy tapes

Reply #2 –
There should also be some speedcorection I guess, cause I can imagine that both tapes won't run for spot on the same time.
I'm pretty sure the guys in audio labs do have such software though, and by seeing the waves the software would do a much better job overlaying that I can possibly ever do myself.

Take the best out of 2 noisy tapes

Reply #3 –
Cassette is going to have ridiculous speed variations...I'm skeptical that you could align two different tapes without it just sounding like a phaser effect at best. But you might have good results if you normalize the speed first with Celemony Capstan. I haven't ever tried it, myself.

Take the best out of 2 noisy tapes

Reply #4 –
Quote from: saratoga on
Assuming you can align them (which may not be trivial), you could average the two which would reduce your noise.


I'd say next to impossible. There is no such thing as 'identical' analog tapes. 2 different tapes from different machines with different speeds, wow and flutter. It will be a demo of 'flanging' from the '70s. The noise processing in Adobe Audition can do wonders if you're careful. The OP should post a 30 second sample to have us give it a shot.

G²

Take the best out of 2 noisy tapes

Reply #5 –
I don't think there's any software you can download or buy to do this, but people have worked on it...

http://www.hydrogenaud.io/forums/index.php?showtopic=100114

http://www.hydrogenaud.io/forums/index.php?showtopic=61012


In the video world, people use a similar technique successfully...
http://www.digitalfaq.com/forum/video-rest...e-captures.html
...but video (even analogue video!) has the advantage of discrete frames and lines, making synchronisation much easier (though not entirely problem-free).

Cheers,
David.

Take the best out of 2 noisy tapes

Reply #6 –
Thanks to you all for the replies!

It was more a hypothetical question as I don't have 2 the same tapes right now.
I was just wondering if it's possible and if there are tools for it.
The same also applies to vinyl I guess? Though the speeddifference might be less or not there at all.

Take the best out of 2 noisy tapes

Reply #7 –
Quote from: Glenn Gundlach on
Quote from: saratoga on
Assuming you can align them (which may not be trivial), you could average the two which would reduce your noise.


I'd say next to impossible. There is no such thing as 'identical' analog tapes. 2 different tapes from different machines with different speeds, wow and flutter. It will be a demo of 'flanging' from the '70s. The noise processing in Adobe Audition can do wonders if you're careful. The OP should post a 30 second sample to have us give it a shot.


I don't think its impossible.  I've done some work synchronizing data from devices that have randomly fluctuating sampling clocks.  That is essentially the problem here.  It can be done if the SNR isn't terrible, its just not easy.

I'd probably start by dividing one tape into short blocks, and then trying to find the optimal (rigid) registration of each block onto the second tape.  Then I'd iteratively subdivide the blocks further and find a new rigid registration for the smaller size.  Since the the tape is a mechanical device with inertia, the speed variations probably follow 1/f statistics.  Since the error is likely to be highly concentrated at lower frequencies, the signal should be oversampled with respect to the power spectrum of the tape speed error, so probably something like a spline interpolation could do ok.  That said, getting the distortion very low would be an interesting challenge.

Take the best out of 2 noisy tapes

Reply #8 –
Quote from: saratoga on
Quote from: Glenn Gundlach on
Quote from: saratoga on
Assuming you can align them (which may not be trivial), you could average the two which would reduce your noise.


I'd say next to impossible. There is no such thing as 'identical' analog tapes. 2 different tapes from different machines with different speeds, wow and flutter. It will be a demo of 'flanging' from the '70s. The noise processing in Adobe Audition can do wonders if you're careful. The OP should post a 30 second sample to have us give it a shot.


I don't think its impossible.  I've done some work synchronizing data from devices that have randomly fluctuating sampling clocks.  That is essentially the problem here.  It can be done if the SNR isn't terrible, its just not easy.

I'd probably start by dividing one tape into short blocks, and then trying to find the optimal (rigid) registration of each block onto the second tape.  Then I'd iteratively subdivide the blocks further and find a new rigid registration for the smaller size.  Since the the tape is a mechanical device with inertia, the speed variations probably follow 1/f statistics.  Since the error is likely to be highly concentrated at lower frequencies, the signal should be oversampled with respect to the power spectrum of the tape speed error, so probably something like a spline interpolation could do ok.  That said, getting the distortion very low would be an interesting challenge.


Have you ever done analog audio tape machine alignment? There are even interchannel phase shifts that are random both during record and play because the tape wobbles side to side in the guides and that's on top of the wow and flutter. Expecting 2 tapes to line up for canceling or averaging is a LOT to ask. Digital it's possible. Analog I'll leave to someone else.

G²

Take the best out of 2 noisy tapes

Reply #9 –
Quote from: Glenn Gundlach on
There are even interchannel phase shifts that are random both during record and play because the tape wobbles side to side in the guides and that's on top of the wow and flutter.

All true, and I'm not claiming what's needed is necessarily possible right now, but TapeRestoreLive fixes those inter-channel issues very well (you can mono the result without nasty phasiness), and the plangent process removes the wow and flutter very well (using the original bias signal as a stable clock which can be recovered and used to fix any tape speed anomalies).

Cheers,
David.