In the slow-speed versión, all eigth tracks are used for two audio channels. Each channel is divided into four subchannels at one-fourth the sampling frequency and recorded on four tracks. Ratherthan periodically subsample the data, the requence of words is split, preserving the pattern of even/odd samples. This preserves manuall editability while improving data recovery in case of a singletrack loss. A 2-channel, medium- speed “Twin Recording” version of the ¼- inch DASH format provides improved cueing and editing performance, affirded by the higher tape speed compared to the low-speedversion. In the twin version, because density and track format are unchanged, each audio channel is recorded twice on separate tracks. Splices can be played without interpolation. However, playing timeis cut in half, compared to the low-speed version.
All DASH tapes carry four auxiliary tracks. The control (CTL) track is a reference track for all digital audio tracks and is synchronous with thesampling rate; one sector corresponds to 48 audio samples. The CTL tracks contains a 4- bit synchronization pattern marking the beginning of sector (groups of four data blocks) a 16-bit control worddescribes the sampling rate and type of format. A 28-bit sequential sector addres provides an internal timecode; its word length is 28 bits, allowing encoding of a time duration beyond the duration ofany tape. It can be used for autolocating or for locking recorders together. After the control tracks is recorded, all subsequent audio tracks are recorded synchoronously to it. A 16-bit cyclicredundancy check code (CRCC) block provides sector error detection. The three other auxiliary tracks are used for stereo or mono cueing , auxiliary data, or conventional timecode.
A linear packing densityis common to all versions and is independent of tape speed: 38,4 kbpi is recorded with 25,6 thousand flux reversals per inch, with a minimum wavelength of 78.2 mils and a maximum wavelength of 235...
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