I've done a fair amount of tape digitalising.
Here's some more things that might help:
Record at 44.1 kHz, 16-bit. Recording at 16-bit gives you a dynamic range of 96dB, although your audio interface might only be capable of a bit less. Cassette tapes without any Dolby can give a dynamic range of up to 56dB. So there's no need to turn up the gain all the way when making recordings, you wont be loosing information. The levels can be changed afterwards very easily, the important thing is that there is no clipping. You should set the gain so that the computer registers the maximum amplitude (the loudest parts of the audio) at between -6 and -12 dB. This will leave some headroom, as the recording level on some cassettes varies over the length of the cassette.
If the cassettes where recorded without dolby originally (ie no dolby sign on the cassette), make sure you play the cassette back with dolby OFF on the deck. It will sound more noisy, with more hiss, but this can be dealt with later in software. Otherwise you will be loosing valuable high frequencies.
In my experience, is there is any phase difference in the left and right channel of the recorded channel, converting to mono can result in loss of high frequencies. Keep a backup in stereo. (Anyone have any experience with this?) Adobe audition has a tool for automatically correcting phase error.
Keep a wav backup of the file before any editing, at 44.1 kHz / 16-bit.
For removing tape hiss, Adobe Auditon's 'adaptive noise reduction' on 'light noise reduction' gives very good results. It doesn't leave a momentary 'swishing' noise after when a silence starts after someone stops speaking, like many other algorithms do. If you send the original recordings to another member who has access to the software, I'm sure they can it for you. Audition has a batch mode, so it's not a lot of work. I could do this for you too.
One more tip: if you happen to have a twin cassette deck, it means you only have to change cassettes every two hours

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