Digital Audio Stationary Head
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The Digital Audio Stationary Head or DASH standard is a reel-to-reel, digital audio tape format developed by Sony in the early 1980's for high-quality multitrack studio recording and mastering, as an alternative to analog recording methods. DASH is capable of recording 2, 24, or 48 channels of audio on a quarter-inch or half-inch wide tape on open reels of up to 14". The data is recorded on the tape linearly, with a stationary recording head, as opposed to in the DAT format, where data is recorded helically with a rotating head, in the same manner as a VCR. The audio data is encoded as linear PCM and boasts strong Cyclic redundancy check error correction, allowing the tape to be physically edited with a razor blade as analog tape would, e.g. by cutting and splicing, and played back with no loss of signal. In a two-track DASH recorder, the digital data is recorded onto the tape across nine data tracks: eight for the digital audio data and one for the CRC data, there is also a provision for two linear analog cue tracks and one additional linear analog track dedicated to recording time code.
There were three families of DASH recorders produced by Sony and Studer, with minimal differences among them:
- 2 track: PCM-3402 and the PCM-3202
- 24 track: PCM-3324, PCM-3324A, and the PCM-3324S
- 48 track: PCM-3348 and the PCM-3348HR, and the Studer D820 and D827
With the exception of the Sony PCM-3348HR and Studer D827, all of the DASH recorders have 16-bit resolution with a 44.1 kHz or 48 kHz sampling rate, although it is possible to use an outboard analog-to-digital converter of up to 20-bit resolution. The PCM-3348HR and D827 are capable of 20-bit 96 kHz operation, and are the only machines that still find significant use today, often in only the highest-end studios for music and film production. All DASH recorders primarily use the SDIF-2 (Sony Digital Interface Format-2) as a digital interface, which is slightly different than the S/PDIF / AES-EBU that nearly all other digital audio recorders utilize. Because of this fact that SDIF-2 is often only found on the expensive DASH recorders, it is also only often found on the highest-end mixing consoles, such as those made by Solid State Logic.
[edit] Tape
The 2-track DASH machines use 1/4" wide tape, while the 24 and 48 track versions use 1/2" wide tape. One interesting thing to note is that the 24-track machines only actually use half of the tape's width, and can be played on the 48-track machines with no modifications. Similarly, the 48-track tapes can be played on a 24-track machine, but only the first 24 tracks are capable of being reproduced. Unlike analog recorders, DASH recorders (as well as any other type of digital recorder) require the use of metal particle-formulation magnetic tape. Analog machines could possibly benefit from the use of metal particle tape, but it would often wear the headstacks at a significantly accelerated pace, so open reel tape of this type was previously not widely available before or after these digital machines were in fashion. Some examples of metal particle tape compatible with DASH machines are 3M 'Scotch' 275, Quantegy / Ampex 467, EMTEC / BASF 931, and Sony's own formulation, typically just typified as 'D', followed by the tape width and length in feet (an example for 1/4" width tape on a 7" reel would be "D-1/4-720").
The DASH format is not compatible with the only other popular open reel stationary head digital recording format, Mitsubishi's ProDigi, which was available as a 2-track or 32-track recorder.
