Audio Engineering

554 Chapter 17

44.1 kHz is obtained by recording three samples per line on 245 active lines at 60 Hz. The
sampling rate is thus locked to the video sync frequencies and the tape is made to move
at the correct speed by sending the video recorder syncs which are generated in the PCM
adaptor.

17.6 An Open Reel Digital Recorder ............................................................................

Figure 17.22 shows the block diagram of a machine of this type. Analogue inputs are
converted to the digital domain by converters. Clearly there will be one convertor for
every audio channel to be recorded. Unlike an analogue machine, there is not necessarily
one tape track per audio channel. In stereo machines the two channels of audio samples
may be distributed over a number of tracks each in order to reduce the tape speed and
extend the playing time.

Analog

to

digital

converter

Digital input

Analog

input

Analog

output

Digital

output

Timing generator

Digital

to

analog

converter

Decode

video

to

samples

Encode

to

pseudo-

video

Video to

VCR

Reference

video to

VCR

Video

from

VCR

Analog Digital

Dub

Figure 17.20 : Block diagram of PCM adaptor. Note the dub connection needed for

producing a digital copy between two VCRs.