5.5.5 Common Systems and Characteristics: Cassette Systems
5.5.5.1 The R-DAT (commonly referred to as DAT) is the only common system to use a cassette format specifically developed for digital audio recordings. DAT tapes have been widely used in field and studio recording, broadcasting and archiving. New DAT equipment is now virtually unavailable. Second hand professional DAT machines are a solution, but present maintenance problems as parts supplies become exhausted.
5.5.5.2 Some last generation recorders operate outside the specification, allowing high resolution recording at 96 kHz and 24 bits (at double speed), others provided Timecode (SMPTE) recording, or Super Bit Mapping, a psycho-acoustic principle and critical band analysis to maximize the sound quality of 16-bit digital audio. 20-bit recordings are quantized to 16 bits using an adaptive error-feedback filter. This filter shapes the quantization error into an optimal spectrum as determined by the short-term masking and equi-loudness characteristics of the input signal. Through this technique, the perceptual quality of 20-bit sound is available on a 16-bit DAT recording. Full quality can only be reached with signals containing frequencies lower than 5-10 kHz. Super bit mapping does not require special decoding on playback.
|
Record/playback mode |
Pre-recorded tape (Playback only) |
||||||
|---|---|---|---|---|---|---|---|
| Standard | Standard | Option 1 | Option 2 |
Option 3 | Normal track | Wide Track | |
| Number of Channels |
2 | 2 | 2 | 2 | 4 | 2 | 2 |
| Sampling rate (kHz) |
48 | 44.1 | 32 | 32 | 32 | 44.1 | |
| Number of quantization bits |
16 (linear) | 16 (linear) | 16 (linear) | 12 (non linear) |
12 (non linear) |
16 (linear) | |
| Linear recording density (KBPI) |
61.0 | 61.0 | 61.1 | ||||
| Surface recording density (MBPI2) |
114 | 114 | 76 | ||||
| Transmission rate (MBPS) |
2.46 | 2.46 | 2.46 | 1.23 | 2.46 | 2.46 | |
| Sub-code capacity (KBPS) |
273.1 | 273.1 | 273.1 | 136.5 | 273.1 | 273.1 | |
| Modulation | 8–10 Conversion | ||||||
| Correction | Dual Reed Solomon | ||||||
| Tracking | Area split ATF | ||||||
| Cassette size (mm) | 73x54x 10.5 | ||||||
| Recording time* (min) |
120 | 120 | 120 | 240 | 120 | 120 | 80 |
| Tape width (mm) | 3.81 | ||||||
| Tape type | Metal-particle | Oxide | |||||
| Tape thickness (μm) |
13±1μ | ||||||
| Tape speed (mm/s) | 8.15 | 8.15 | 8.15 | 4.075 | 8.15 | 8.15 | 12.225 |
| Track pitch (μm) | 13.591 | 13.591 | 20.41 (wide track) |
||||
| Track angle | 6°22’59”5 | 6°23’29”4 | |||||
| Standard drum | Ø 30 90° Wrap | ||||||
| Drum revolution speed (r.p.m.) | 2000 | 1000 | 2000 | 2000 | |||
| Relative speed (m/s) |
3.133 | 1.567 | 3.129 | 3.133 | 3.129 | ||
| Head azimuth | ±20° | ||||||
Table 1 Section 5.5 Specifications for various record/playback modes of DAT for both blank and pre-recorded tapes:
5.5.5.3 Phillips DCC (Digital Compact Cassette) system was (unsuccessfully) introduced as a consumer product and offered limited compatibility with analogue compact cassettes through the ability to replay analogue cassettes on DCC equipment. DCC is now considered obsolete.
| Format | Variants | Carrier Type | Audio and data tracks | Digital Audio Standards supported | Interface |
|---|---|---|---|---|---|
| DAT or R-DAT | Timecode is not part of the R-DAT standard but may be implemented in Sub-Code. Some pre-recorded DATS use ME tape | Cassette with 3.81mm metal particle tape. | Stereo. Subcode includes standardised markers plus user bits for proprietary extensions | 16 bit PCM @ 32, 44.1 and 48 kHz | AES-422 on professional machines. SP-DIF standard |
| DCC | Cassette with 3.81 CrO2 | Stereo, metadata standard supports minimal descriptive data | PASC compressed PCM (4:1 bit rate reduction) | ||
| Videotape based formats — see table 4 |
Table 2 Section 5.5 Digital Audio Cassettes
