Audio Engineering

Digital Audio Recording Basics 563

machine with a single head. At such a low frequency, conventional inductive heads that
generate a voltage from fl ux changes cannot be used, and DCC has to use active heads
that actually measure the fl ux on the tape at any speed. These magneto-resistive heads
are more complex than conventional inductive heads and have only recently become
economic as manufacturing techniques have been developed.

Data reduction relies on the phenomenon of auditory masking and this effectively
restricts DCC to being a consumer format. It will be seen from Figure 17.30 that the data
reduction unit adjacent to the input is complemented by the expansion unit or decoder
prior to the DAC. The sound quality of a DCC machine is not a function of the tape, but
depends on the convertors and on the sophistication of the data reduction and expansion
units.

17.9 Editing Digital Audio Tape ...................................................................................

Digital recordings are simply data fi les, and editing digital audio should be performed in
the same way that a word processor edits text. No word processor attempts to edit on the

Figure 17.29 : In DCC audio and auxiliary data are recorded on nine parallel tracks along

each side of the tape as shown at (a) The replay head shown at (b) carries magnetic poles,

which register with one set of nine tracks. At the end of the tape, the replay head rotates

180 ° and plays a further nine tracks on the other side of the tape. The replay head also

contains a pair of analogue audio magnetic circuits that will be swung into place if an

analogue cassette is to be played.

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Digital track distribution 107.5

(a)

(Dimensions in millimetres)

3730

10 1852.5

(3780)

(b)

Head rotation

A 1

A 2