Alesis ADAT-XT20 User Manual download pdf (Page 113)

Appendix A: Digital Recording Concepts

112 ADAT-XT20 Reference Manual

APPENDIX A

DIGITAL RECORDING

CONCEPTS

ANALOG RECORDING BASICS

Digital recording works very differently from analog recording. With analog

recording, tape containing millions of tiny magnetizable particles move past a

record head. The magnetic field around this head fluctuates according to the

audio signal present at the tape recorder’s input. These fluctuations

permanently rearrange the particles on the tape to form a pattern that is

analogous to the original audio signal.

On playback, the patterns on tape are read by a separate playback head (or

from the record head, set up to read instead of record signals) that converts the

magnetic fluctuations back into an audio signal.

The biggest problem with analog recording is that the tape itself alters the

sound originally recorded on tape. Tape hiss is one problem; it superimposes a

low-level rushing noise onto the audio signal. Although there are ways to

minimize noise, such as noise reduction circuitry, this colors the sound in the

process of masking the noise.

Tape’s frequency response is also an issue. Tape has a hard time “absorbing”

higher frequencies, which can dullen the sound. Moving tape faster allows the

heads to magnetize more particles and extends the high frequency response, but

the tradeoff is increased tape costs, and heftier transports to move bigger reels

of tape.

DIGITAL RECORDING BASICS

With digital recording, the technology is very similar — tape moves past a

record head, and plays back through a playback head. However, the signal

recorded on tape is very different.

Audio signals entering each channel of the XT first pass through an analog-to-

digital (A/D) converter, a device that takes 48,000 samples or “snapshots” of

the signal level every second

. Each sample is assigned a specific numeric value

that corresponds to its level.

A/D

Analog Signal Digital Signal

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Alesis ADAT-XT20 User Manual Page 113