I've got a lot of old 7 inch singles and lp's I want to digitize, but it's almost impossible to get them played correctly because on most of these records the hole isn't really pressed in the middle of the record. I've tried Audacity and load of other audio correcting software, but I keep hearing the pitch change. I've tried several different record players but they all give the same result. Is there anybody out there who found the ultimate solitions? I for one would be very grateful, since tnis has been bugging me for years now. Thanks in advance
I have personally done this once. I had a recording that had obviously been copied from a source that had been recorded or played back at uneven speed. By listening to parts where the high and low points in the modulation were clear, and looking at the audio in spectrogram mode in an audio editor, I was able to identify the speed of the modulation, and then applied an inverse modulation. With a bit of trial-and-error I was able to get a satisfactory result.
The good news for you is that the modulation will be at a constant rate throughout the song. With a record playing at 45 rpm, the modulation will have just that rate, 45 rpm, or 0.75 Hz. Unfortunately, the depth of the modulation (how much higher and lower the frequency goes) depends on how far the hole is from the actual center of the record; so you won't be able to find settings that work for one record and then apply them to all the records. A bit of trial-and-error will always be needed to find the correct settings.
Practically, try to find a part of the song where the modulation can easily be measured, e.g. an isolated instrumental part with long notes, preferable on an instrument that doesn't have strong vibrato of itself. Once you have identified the location of the high and low point, and the depth of the modulation, you can then apply the opposite modulation (using a sine wave as modulator) to the whole song.
There is a commercial tool available for this: Capstan by the same company that makes Melodyne.
It's rather expensive, however (about 3800 EUR to buy, 200 EUR to rent for five days).
It can certainly be done. I'm thinking of the recent 'stereo' versions of some Glenn Miller recordings. At the original session as well as the main recording there was a backup recording to another machine through its own microphone. It proved possible to synchronise these well enough to derive stereo information. Whatever computer did that should be quite capable of compensating for an off-centre hole!
But, practically, I think you'd be better off contriving a mechanical method of centering the disk. Maybe drill out the centre - aligned correctly this time! - and use one of those adapters made for ex-jukebox singles? Or just bore it out a bit and use packing.
The subject is discussed here:
This is possible but probably rather complicated. Audacity should work but you would have to calibrate the speed changes over a single rotation. I'm not sure if the correction is different on the outside or inside groves; I think it is. Perhaps you could calculate the correction then use audacity to apply that correction. It's a calculus problem to calculate the rotational speed of an off-center disk taking into account the movement from outside to inside.