Compression
Overview
- After capture, WAV files are ftp'd to a temporary holding area on gigue, an RS/6000 AIX server housed on the third
floor of the Music Library.
- A batch job runs nightly to compress the files into MPEG-1 layer II format (384
kbps) using software developed by IBM.
- The compressed files are used for playback and the original WAV files are stored
on tape in the rare book vault in the Music Library.
MPEG-1 Layer II
- Lossy perceptual audio encoding method based on psychoacoustic models of the
ways in which the human mind interprets sound.
- Compression ratio (approximately 3:6:1) chosen based upon subjective
comparison testing between original and compressed files by students, faculty, and
library staff.
- Compression reduces space needed for storage and network bandwidth with little
loss of audio quality to the listener.
Future Plans
- The following emerging formats will be investigated as possible replacements for
MPEG-1 Layer II during the next year:
- MPEG-1 Layer III ("MP3")
- Dolby AC-3
- AT&T's PAC
- MPEG-2 AAC