A bunch of good suggestions were made already. From the "Let's Get Ridiculous About It" department:

If you're really a stickler about getting the best possible sound quality out of an old cassette, you might consider looking around for a Nakamichi Dragon cassette deck. If you can beg, borrow, or steal one in good condition. Reason is, this cassette deck had a servo mechanism to adjust the azumuth of the play head to best match the recorded signal on the tape, and indeed, it will continually adjust the azimuth as the tape plays, which will give you the best high-frequency response possible out of any given tape. Plus, this deck's level of quality in the playback preamps will give you the best S/N ratio, too.

If you can't find a Dragon, some cassette decks allow you to adjust the azumuth of the play head manually, i.e. with a small screw on one side of the play head. If you listen carefully using headphones, you can sometimes get a big improvement in the highs in the playback, as you slowly adjust the azimuth screw. Don't turn it too far, or you can encounter what's called a "side peak", a small peak which is not the maximum. For old-time analog tape recorder geeks only. And I qualify, since I still have a set of reel-to-reel MRL calibration tapes buried somewhere around here. :-)

Once you get the best possible quality signal from your cassette deck, it's mainly a matter of keeping levels in your signal chain as high as possible before distortion, for the best S/N ratio, up to and including your A/D converter. I would use a minimum of 24-bit, 48 kHz for the digital conversion. You can always downsample/dither it later for transfer to CD or whatever.

Regards,
Doug

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