Bay Area Moviegoing: Theatrical Digital Sound Formats

updated Monday, 01-Mar-2004 22:24:20 PST by sparCKL@snout.org

The information below is reproduced from http://home.att.net/~reyito/digital.htm. As the author says: Which format is better depends on personal taste.

Most modern movies are released in at least two of the digital formats listed below, in addition to having the standard analog sound track. You should always check theatre listings to determine what sound format a particular movie is actually being presented in.

The digital movie sound formats of today deliver from six (Left, Center, Right, Left Surround, Right Surround, and Low Frequency Effects or Subwoofer) to eight channels (same as the six-channel format plus Left Center and Right Center channels across the front) of clean dialog, music, explosions, bass, Foley effects, and other sound effects. The formats in use today are:

Dolby Digital (DD)
http://www.dolby.com/digital/

Up to five full-range channels (L-C-R-LS-RS @ 20Hz-20kHz) and a 20-120Hz LFE channel in a 384 kbps (kilobits per second) bitstream (a single line of digital data) (Note: bitstream on a movie filmstrip is 320 kbps; DVD uses up to 448 kbps)
Resolution: 20-bit @ 48kHz sampling rate
Compression: about 11:1, by AC-3 algorithm
115 dB dynamic range for LFE channel; 105 dB dynamic range for the other channels
Where on filmstrip: gaps between sprocket holes
Backup: analog tracks (Dolby SR, Dolby-A, mono)

DTS Digital Surround
http://www.dtsonline.com/

Up to three full-range front (L-C-R) channels, two 80Hz-20KHz surround channels and a 20-80Hz LFE channel in a 1544 kbps (or 1.544 Mbps) bitstream (laserdiscs use two bitstreams that add up to 1.544 Mbps)
Resolution: same as Dolby Digital
Compression: about 3:1, ADPCM-based
96 dB dynamic range
Where on filmstrip: timecode along edge of film frame; it is read and synchronized with CD-ROMs on custom-made 3-disc reader
Backup: analog tracks (Dolby-compatible)

SDDS (Sony Dynamic Digital Sound)
http://www.sdds.com/

Up to five full-range front channels (L-LC-C-RC-R), two full-range surrounds (LS,RS) and an LFE channel (frequency range should be similar to Dolby Digital's); no information about bitrate on hand
Resolution: 16 bits @ 44.1 kHz sampling rate, ATRAC-based (like MiniDisc)
96 dB (approx.) dynamic range
Where on filmstrip: on either side of sprocket holes (two separate bitstreams are offset by several frames to provide a digital backup track in case of tears or bad splices)
Backup: one digital bitstream (read above) plus analog tracks

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