There is a mention (p. 48) in Peter Wright's book 'Spycatcher' about use of a tape recorder with two heads to give listeners a slight delay in one ear for the purpose of *improving* voice intelligibility when transcribing tapes.
TLC flash stores three bits per cell, a trick which requires the hardware to reliably distinguish eight distinct levels of charge on the floating gate. Three times the capacity of SLC flash; 1.5 times the capacity of MLC.