All the usual issues are widely noted but a recurring issue is controlling "levels" so not to overload any input along the way.
Keep trying.
Bob
Recording audio via 'line in' from Tapes, LP's, etc, all with faultless material frequently results in an very distorted audio file.Monitoring during recording is faultless, thus proving medium, player, leads and connections and Sound card ( Creative 'Sound Blaster "live' 5.1 - 2 such cards tried, same result), also speakers. The OS is Windows XP with SP2. The track either side of the faulty one can be faultless, (as can an immediate re-recording). I have used several different recording software prgrammes, with the same effect.

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