Spirit Digital 328, User Manual

SECTION 1: The Basics Of Digital Mixing

5

C. The Question Of Levels

In the world of digital recording, you have to treat

levels with a little more respect than in analogue

systems in order to avoid distortion. This is

because of the very different ways in which ana-

logue abd digital systems work.

We know distortion when we hear it, but how

does it arise? Put simply, distortion is an unwant-

ed change in the audio waveform, usually caused

by the clipping of the audio waveform. As you

crank up input levels, you reach a point where the

system cannot recreate at the output the extreme

peaks and troughs at the input – and that’s distor-

tion. In analogue circuits distortion tends to come

on gradually, increasing in severity as input levels

are increased. Because it can sound good to the

human ear, some types of analogue distortion

have long been exploited in the studio –  to warm

up drum sounds by recording ‘hot’ to tape, by

using tape saturation characteristics. So, although

the point at which distortion begins can usually be

quite well identified, you can generally ‘push’ this

level a little without ruining your recording. 

Digital electronics, on the other hand, deal with

a precisely defined range of levels. As you increase

the level going into an analogue-to-digital convert-

er, the numbers coming out get bigger and bigger

– until you run out of resolution at the convert-

er’s maximum input level, and you have the sud-

den onset of distortion. For reasons which are too

tedious to go into, digital distortion doesn’t sound

at all pleasant, and it’s therefore very important to

avoid exceeding maximum levels.

Metering also works differently. In analogue

mixers and recorders, equipment is designed to

operate at various operating levels, such as

+4dBV (most ‘professional equipment) or -

10dBU, and the relationship between 0dB on

meters and the point at which distortion starts is

not fixed. Also, because distortion comes in gradu-

ally, you can almost always get away with pushing

your meters some way into the red.

In a digital system, metering is relative to

0dBFS, which is the point at which the system has

run out of numbers and you cannot go any higher

without creating distortion. There is no LED on a

bargraph meter above this, because there isn’t

anywhere else to go. Because distortion occurs as

soon as you exceed these levels, whenever you’re

setting levels bear in mind that even peaks should

not light the red LEDs at the top of the 328’s

meters, though this might feel right if you’re used

to working with analogue mixers. 

D. The Future

Because digital audio technology rides benefits

from progress in the very fast moving area of

computer technology, things are always moving

ahead. From 16 bits and 44.1kHz, we’ve moved

on to a point where 20 and 24-bit recorders are in

use, some with 96kHz sampling. The need to

move greater amounts of data around means that

new interface standards will appear. Firewire

(IEEE1394) is already establishing itself as a use-

ful transfer protocol in digital video, though it may

soon also be used in audio. Another trend that is

is likely to continue is the use of cheap, powerful

consumer or business computers to run increas-

ingly powerful audio software, software that can

take over more functions previously performed by

dedicated hardware.

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