I had not used Audacity in quite a while and had no idea that it had been improved so much as to include a sample noise remover filter. This is most excellent for a freeware offering. Although not as elegant and easy to use as Amadeus, if you are just doing a few tapes here and there, this would be the way to go to keep expenses down.
Forget overdubbing. You just need to get one good original from your tapes. How you do that depends on the equipment available. The Technics deck would be fine, IF it plays the tapes well. Make sure the heads, rollers and capstans are clean. Plug the output RCAs into the Mac and record the music accordingly. Make sure to save this as your master recording and burn the files to CD. Never do any noise reduction on your original!
Once you have a duplicate copy, start the noise reduction process with Amadeus or Audacity to remove tape hiss. If you want more bass or need to bring out some highs, use the EQ filters, but do not OVER EQ. Use your Normalize filter to make sure the audio level is appropriate.
This should result in a good archive of precious tapes.
You misunderstood what they were doing with the Black Sabbath tapes. What they mean by overdub is that, say there was something wrong with the bass track (because of age or damage). The studio can pot down the track with the bass, and the origianl bass player can come in to the studio and "overdub" the damaged area in order to repair it. They can then add reverb to simulate the arena and it should sound almost exactly like the damaged portion.
You are not doing anything near this. If you try to overdub your stereo tapes, you will get what is called "phasing". That is, two identical tracks with slight variation causing audio conflict.
Audacity is GREAT! I am doing the same type of project, preserving old cassette tapes before the oxide falls off, and it has saved me a ton of time and expense.
