Audio Engineering

Digital Audio Recording Basics 555

52 256

Control

bit

0.3 70

0.3

0

1

Data

512

Data

Figure 17.21 : Typical line of video from PCM-1610. The control bit conveys the setting of
the preemphasis switch or the sampling rate, depending on the frame. The bits are separated
using only the timing information in the sync pulses.

Digital

to

analogue

convertor

Timebase

correction



error

concealment

De-interleave



correct

errors

Data

separator

External sampling

rate reference

Out

In

Capstan

Analogue

to

digital

convertor

Timing

Time compress



odd/even

shuffle

Interleave



add

redundancy

Channel

code

Figure 17.22 : Block diagram of one channel of a stationary head digital audio recorder.

See text for details of the function of each block. Note the connection from the TBC to

the capstan motor so that the tape is played at such a speed that the TBC memory neither

underfl ows nor overfl ows.

The samples from the convertor will be separated into odd and even for concealment
purposes, and usually one set of samples will be delayed with respect to the other before
recording. The continuous stream of samples from the convertor will be broken into
blocks by time compression prior to recording. Time compression allows the insertion of
edit gaps, addresses, and redundancy into the data stream. An interleaving process is also