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  • gutted
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'Remastering' of an old cassette recording
I have several old recordings - originally from cassette - that I'd like to try and improve.  Or 'remaster' 

Anyway - there's one particular distortion effect that I want to try and correct, but I'm not entirely sure what it's called, so unsure which tools to search for.  I think it might be wow & flutter, but the research I've done so far would suggest that wow & flutter involves periodic change in pitch of the audio (due to periodic variations in speed of the cassette).

The effect that I want to correct for is certainly periodic and obviously has a frequency, but it doesn't sound like the music is speeding/slowing.  Instead, the music sounds like it's periodically getting slightly muffled then slightly clearer, slightly muffled then slightly clearer, slightly muffled then slightly clearer.  Perhaps this actually is wow & flutter (?)

Can anyone help me identify this distortion so I know what tools I'm looking for to see if I can make it any better.

I currently use Audacity, so any sort of plugin for that would be interesting.  Of if anyone can suggest other tools that I may be able to download/buy for the purpose, that would also be of interest.

Cheers!
Dan.

  • cliveb
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'Remastering' of an old cassette recording
Reply #1
The effect that I want to correct for is certainly periodic and obviously has a frequency, but it doesn't sound like the music is speeding/slowing.  Instead, the music sounds like it's periodically getting slightly muffled then slightly clearer, slightly muffled then slightly clearer, slightly muffled then slightly clearer.

Sounds to me like it's a tape head contact problem. If your playback deck isn't dual-capstan, then the internal mechanics of the cassette shell can radically affect head contact. In this case my guess is that the feed spool has a sticky spot that causes a "snag" once per revolution, which would be about every couple of seconds. One possible solution would be to transfer the tape and spools to a different shell, although if the problem is on the spool hub itself rather than the shell, that may not work.

  • gutted
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'Remastering' of an old cassette recording
Reply #2
Ah, sorry - I should have been clearer.  This is an old recording that was originally from cassette - but I don't have the cassette itself.  I have an MP3 of the recording.

Even though the MP3 is a high bitrate, the playback is very poor.  I'm wondering if I can use any software to play around with the MP3 file(s) I have here to improve things.

And for clarity - this is a a recording that I got from someone else.  Just listening to it, and given the context, I'm 100% sure it was originallly recorded on cassette but I have no idea of specifics (e.g. I don't know the tape material and/or bias etc).

Basically I'm starting from scratch with an MP3 recording which has pretty poor playback.  I can imagine that I'll never get the sound to be "good", but the periodic fluctation in sound makes me wonder if I can apply some sort of digital technique to at least remove that distortion effect if nothing else...

What do you reckon?

'Remastering' of an old cassette recording
Reply #3
I think you're stuck with it personally.

It sounds to me as though it may have come from a cassette tape that had been left laying in the sun for too long. A friend of mine used to have exactly the same problem with cassette tapes in his car until I suggested that he make new recordings and stored them in their cases under his driver's seat rather than leaving them laying around on his dashboard out of their cases in hot, sunny weather.

As you only have the MP3, this information is of no practical use to you. It may explain why it sounds the way it does though.

Cheers, Slipstreem. 

EDIT: FYI - Wow is periodic variations in speed that make the tape sound like a vinyl record with an offset centre hole and flutter sounds like a constant gargling effect. It sounds to me as though you're hearing cyclic HF loss on these particular recordings. Almost as though somebody is winding the treble control up and down constantly and repeatedly.
  • Last Edit: 26 June, 2008, 12:23:50 PM by Slipstreem

  • pdq
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'Remastering' of an old cassette recording
Reply #4
It sounds to me as though it may have come from a cassette tape that had been left laying in the sun for too long.

Another important point about storage of tapes is always to store then on edge rather than flat. If you store then flat then gravity gradually distorts the tape The same is true for vinyl. Of course, all of this is becoming less and less important as we move away from tape and vinyl.

  • gutted
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'Remastering' of an old cassette recording
Reply #5
Thanks Slipstreem.  Yeah, the effect is kind of similar to someone adjusting the treble up and down throughout playback I guess.

I was hoping it was a common enough effect that some clever soul has built a plugin for Audacity or something.  But I am denied.  Harsh.

Ah well - thanks again dude, and all other guys who replied.  It's better to have this distorted copy than nothing at all, so I shall consider myself lucky!

  • BobO
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'Remastering' of an old cassette recording
Reply #6
Thanks Slipstreem.  Yeah, the effect is kind of similar to someone adjusting the treble up and down throughout playback I guess.

I was hoping it was a common enough effect that some clever soul has built a plugin for Audacity or something.  But I am denied.  Harsh.

Ah well - thanks again dude, and all other guys who replied.  It's better to have this distorted copy than nothing at all, so I shall consider myself lucky!


I wonder if you could take the file, load it into Audacity, and manually create shape envelopes along the length of the track that follow the ebb and flow of the HF loss, and which would allow you to correspondingly boost and recede the HF along that path. Presumably you could put back some of the lost HF and even out the sound.

Your high-end noise floor would go up and down too, but you might end up with something better than what you started with.

  • Last Edit: 26 June, 2008, 05:25:21 PM by BobO

  • jesseg
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'Remastering' of an old cassette recording
Reply #7
It's possible it could be better.  The improvement also hinges on how linear the treble loss is.  That is to say...  if there's dynamics changes when the treble gets reduced.  It's likely there is.  That could also be corrected for somewhat, but this is getting into some really complicated stuff.

[edit]
if you would like to upload a 30 second clip or so, i can run it through some audio processing that I have which exceeds the capabilities of "hardware" like Omnia6EXi, Orban8585, etc... and some might say sounds better than them too. (even people from orban and omnia, and other manufacturers)

and we'll see what it can do with em, if you want.  please use mp3DirectCut to slice the clip out of your original mp3 if you can, so I can ensure the mp3 gets decoded properly directly to 32bit.  if not, decode it to wav using lame, and cut the wav down to the clip you want, and upload as wav or flac.

chances are it'll just sound like a polished turd - what it would be regardless of how it sounds.
[/edit]
  • Last Edit: 26 June, 2008, 06:20:36 PM by jesseg

  • gutted
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'Remastering' of an old cassette recording
Reply #8
Thanks for the suggestions, guys.  And jesseg: thanks for your offer!  I'll upload a sample - thanks