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WPI Technical Theatre Handbook: Digital Audio Tape (DAT)
 
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Digital Audio Tape (DAT)

A significant advance in tape technology has given the industry the DAT (Digital Audio Tape). DAT addresses many of the problems associated with standard tape, but does not solve all of them.

Standard tape employs an analog method of recording. That is to say, at any given time, the voltage coming off of the playback head in a tape deck may be any voltage within a certain range. This voltage directly represents the sound recorded on the tape. With DAT, what is stored on tape is a digital representation of the sound. All that is being read off of the tape are binary data -- ones and zeroes.

Digital recording schemes work by sampling (reading) an analog signal many times a second. Each sample is a representation of what the continuous analog wave (the sound) is ``doing'' at a particular time. However, it is not an entirely accurate representation of the sound, as there are a discrete number of representations for each sample. That is to say, where an analog signal can be any value in between two end points, a digital sample can only be one of several values in between those points.

DATs sample at either 44.1KHz (44,100 times a second) or 48KHz (48,000 times a second)6.1. DAT decks sample with a 16-bit resolution, meaning 16 individual ones or zeroes are used to represent one sample. This translates to each sample being any of 65,536 values. The faster the sampling rate and more bits of resolution yield a more accurate representation of what's being recorded. It should be noted that no digital recording method is as accurate as analog methods, because digital methods are only approximations of the analog signal.

Several advantages make DAT more appealing than standard tape. A scheme of indexing and cueing is included, thus it is fairly easy to cue with DAT. However, seeking between cues is not instantaneous, as the tape must still be physically moved to the proper position. DAT is also relatively free from the noise problems associated with analog tape.

Even with DATs advantages, it is still a tape, and thus isn't exceptionally robust. Quality DATs can last a considerable period of time, but when they start to degrade the effects are quite noticable. As the magnetic oxide flakes off of the tape, the DAT deck becomes incapable of reading the data, and produces a noise somewhere in between an explosion and someone scraping their fingernails on a chalkboard. Needless to say, this is less than desirable. This and the problems with cueing make DAT more suited to recording effects and music for a production for playback in some other digital format such as compact disc.


next up previous contents index
Next: Compact Disc (CD) Up: Input Previous: Analog Tape   Contents   Index
Steve Richardson 2000-07-06

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