I am digitally capturing several old cassette tapes for a friend, and one of them - that was published in 1983 and has sat on a shelf for more than 30 years - suffers from cyclical pitch modulation or "warble". I suspect it's due to tape stretching because it gets significantly more pronounced near the end of the spool. At any rate, it's not the USB player I'm using, as only this one tape is affected, and it's consistent.
I've run the tape through several times hoping it might just be a "stickiness", "dry rot" or contaminant problem...no luck. Since the pitch modulation is cyclical...does anyone know of an Audacity (or similar) plugin that might allow me to repair the audio? I've done a fair amount of Googling and, except for professional-grade tools, no one's had any ideas. But then again, most of the posts I found were 5+ years old.
Thanks in advance.
Sorry I can't recall any names but quite some time ago, perhaps 10 years even, software was developed that reportedly achieved what had previously be consider impossible. There were some reports about it from a couple of users on the Syntrillium forum (Audiomasters) but that is defunct now. A backup of all posts was maintained on another server for some time but that too eventually disappeared (but might exist somewhere?). Some of the main technical people from Syntrillium became active on the Audition forum and might still be reachable there (Syntrillium was the developer of CoolEdit, which became Audition when purchased by Adobe).
Anyway, its main use to these people was with phonograph disks. Reportedly it did a marvelous job with warped disks or those with off center holes, the symptoms of which are probably the same as your damaged tapes. At the time it was quite expensive, only reasonable for professional (money making) use or perhaps by very wealthy amateurs. Still, after all this time, it might be more affordable.
haven't heard of that, you would (maybe) need to implement your own, it would be like a resampler which can interpret input as varying sample rate signal, and then you'll need to figure out a couple of other variables (like, speed of rotation and the speed difference at the beginning and at the end of the recording). possible but definitely not easy, it sucks if this is the best record you have.
There is a company called Plangent that has successfully removed wow from audio recordings by recovering the bias frequency from the recording and using that as a reference frequency. The technique works, but I suspect that the cost is out of your ballpark.
Celemony Capstan (https://www.celemony.com/en/capstan) claims to do that, but it's $200 USD to rent for 5 days or $4500 to buy!!!!!
If it is really is as you say, cyclical, you could undo it with vibrato. A VST vibrato, or Reaper DAW vibrato. If a sine wave waveshape for the modulation of pitch does not do it then I think you can draw your own, but I have not tried it.
You could obtain the pitch control data for the whole recording by ear. Record midi control data into a midi channel while playing the audio at a slow speed.