Scrape Flutter refers to an audio error caused by physical problems with analog tape media.
Scrape flutter is caused by too much friction between the tape transport and the tape itself. The friction may be present at any point the tape touches the deck: at the guides, both moving or stationary; at the heads; or at multiple points along the tape path simultaneously.
The friction causes the speed of the tape across the heads to slow momentarily, at which point the tension along the tape in parallel to its path increases until the tension force overcomes the inertia of the friction, causing the tape to suddenly move forward at a speed higher than playback. This variable speed process happens in microseconds and the result in the output signal is flutter.
Scrape flutter is an audio artifact that sounds a bit like bad mp3 compression. There is a sort of swirling, whooshing noise in the high-midrange of the audio spectrum. This artifact is identifiable in the audio signal, and may be accompanied by an acoustic squealing noise coming directly from the tape deck, which may or may not be present in the audio signal.
Can it be fixed?
The issue can be mitigated, depending on the physical condition of the tape. If the tape is scraping due to sticky-shed or soft-binder then baking can help fix the problem.
If the problem is due to loss or failure of the tape lubrication then baking will not help. Instead, many specialists use oil specially formulated to lubricate the tape’s path over the guides or heads of the deck.