|The R-DAT (Rotating-head Digital Audio Tape) recorder or DAT is a digital audio recorder that makes use of tape transport and rotating head technology originally developed for video recorders.|
The DAT system houses the tape in small cassettes roughly half the size of a standard analog cassette and is protected from dust and handling by the same kind of hinged door used for video tapes. As with analog cassettes a sliding write protect tab is provided to prevent accidental erasure. Tape recording times of up to 2 hours are possible with DAT.
The tape is drawn out of the cassette housing by the tape transport and wrapped around the rotating record/playback head. As in helical scan video systems the drum rotates at high speed and lays the digital audio information on the tape in a series of closely spaced diagonal lines with a resulting high information density on the tape. Fast forward and rewind times are very fast with a two hour tape rewinding in about 45 seconds.
Most DATs house the tape transport and digital audio processors in one enclosure although some manufacturers separate these functions. The audio processing functions include both analog-to-digital conversion (ADC) and digital-to-analog conversion (DAC) plus anti-aliasing filters. Most professional DATs are capable of recording and playback at a number of sampling rates with the most usual being 44.1 kHz and 48 kHz.
|Subcodes||Subcodes are information written on the tape independently of the digital audio portion. They allow the user to arbitraily number and mark selections on the tape in order to search or skip portions of the recorded material.|
|Program numbers||Program numbers are added in numerical order and can be used to locate selections.|
|Start ID||Start ID marks can be added either manually or automatically. If manually set they can occur anywhere in the recorded program. If automatically set the machine uses a level threshold to decide where to place marks. If the program level has been below the threshold for more than two or three seconds a mark is placed at the next place which exceeds the threshold. Start ID marks can be erased at any time and in any order.|
|Skip ID||Skip ID marks allow a portion of the recorded program to be marked so that when the machine senses one of these during playback it will stop and enter fast forward mode until it reaches the next Start ID where it will continue playing.|
DATs provide both analog and digital I/O. By using
the digital I/O it is possible to limit the number of times the digital
signal is passed through the D/A-A/D converters until final playback when
the digital signal must be converted to analog for amplification and loudspeaker
dissemination. By keeping the signal in the digital domain signal loss
and noise which might be introduced by analog components is kept to a minimum.
Several types of digital connectors are used with DATs. The most common are RCA, BNC, and XLR type connectors. Analog connectors are usually of the unbalanced RCA or balanced XLR type.
machines provide peak meters using bar graph type level indicators.
These are not VU meters and a reading of 0 is the absolute maximum level
the machine can achieve without distortion. If peaks are reaching or exceeding
0 the level is too high and input level should be reduced.
Some DAT machines provide a headroom indicator which keeps track of the highest signal peak since last being reset. This provides a handy way to tell if your program has reached or exceeded the 0 level maximum of the machine. This is a very useful feature as it is not always possible to pay such close attention to levels when recording, mixing, or mastering.