precision adaptive subband coding (MPEG) (PASC)

Precision Adaptive Subband Coding (PASC) is an MPEG-based data reduction process used in Digital Compact Cassette( DCC). The goal of the PASC process is to store digitized audio in CD sound quality on audio tapes.

PASC achieves this by optimizing two factors that determine audibility: The first effect considered in PASC is the hearing threshold. The hearing threshold is the volume at which human hearing begins in the first place. It is frequency dependent and characterized by the fact that hearing is more sensitive at medium frequencies than at low or high frequencies. PASC takes this into account by processing only sounds above the hearing characteristic.

The second effect is the loudness, which is subject to a certain dynamic in the perception and changes the hearing threshold. This means that with louder sounds the hearing threshold automatically increases. This dynamization of the hearing threshold is also taken into account in PASC.

The PASC process is highly efficient, requiring only a quarter of the bit rate compared to pulse code modulation( PCM) for the same sound quality. PASC relies on the MPEG standard and has a bit rate of 384 kbit/s.