A good rule of thumb is to do a mixdown of your tune first, and then record it on a cassette out of the 4-track into in a regular deck.
I find that bouncing track's (in the 4-track) to achieve a stereo mix will degrade the quality when it's done more than a few time's.
it's better to just record on all 4 track's and then do a good mix.
if You need to do an overdub just ffwd the 4-track tape past the ending of your song. Record the mix you just recorded into the regular deck back onto the 4-track tape. Then you got 2 more track's to do some overdub's.
Repeat this as many time's as it take's to complete your song.
Here's the sequence in order.
1)Record all track's, mix, dump onto regular tape deck.
2)ffwd 4-track till blank tape, record mix from regular tape deck into 4-track.
3)use open track's for overdub's.
Repeat step's 1,2,3 till song is complete.
The idea here is that you'll be using a fresh part of tape (on each deck)everytime. Therefore no real loss of quality.
of course I agree that the method I'm suggesting is a bit primative, but it work's the best to achieve the highest quality IMO. especially when you're working with only 4 track's, and using cassette tape.
Buy a digital 16 track studio next time damn it

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Tripp.