Interesting Film Sound Info

Info on the three different digital audio systems in use in movie theaters

• DTS (Digital Theater Systems) has the 6 channels of audio on one or two CD ROMs synchronized to the film, 1.5 megabit bit stream. One channel is reserved for the subwoofer or LFE (low frequency effects) as it is called in the industry. DTS is the best system and uses the least amount of compression. DTS time code is printed between the picture and the analog track.

• SDDS (Sony Dynamic Digital Sound) has its bit stream printed outside of the sprocket holes. Both sides are identical but are staggered in time. SDDS usually hiccups at splices. It is a 7.1 staggered in time. SDDS usually hiccups at splices. It is a 7.1 channel system, 3 behind the screen, 2 surround channels on the left side of the seating area, and 2 more on the right side. Some theaters fold it down to 5.1, with one left and one right surround. The 0.1 channel is for the subwoofer.

• Dolby Digital is a 5.1 channel system over which there is much controversy due to its very low bit rate of only 320 kilobits/ sec and extreme compression. It uses “bit pooling” so that if only one or two channels are active at a given moment, it or they get most of the bits. But when all 5.1 channels are active you can hear it run into trouble. Dolby Digital bit stream is printed “between” the sprocket holes.

Related Additional Info

• Some movies are analog only, usually in stereo; some also have one of the digital systems on the print, some have two digital systems on them and the big budget movies have all three.

• If a theater has one type of digital equipment but the movie does not have that system, that movie is played in analog. All three digital systems can revert to the analog track in the event of trouble.

• Most theaters that have digital are equipped with DTS because DTS is the least expensive system for a theater owner to install. This is ironic when you consider it is the best system. DTS can also supply CDROMs in different languages. Currently DTS is the only system that can be put on 70 mm film but no movies are released on 70 mm anymore and very few theaters have 70 mm equipment.

• Dolby Digital at the slightly higher bit rate of 384 kb/sec has been selected as the mandatory audio format for digital HDTV. This has caused much controversy. Dolby Digital is also the mandatory audio format for DVD.

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