dbx 160X Manuel d'instruction - Page 7

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4.0 TYPICAL APPLICATIONS

4.1 SMOOTHING

VARIATIONS IN

VOCAL

LEVEL

When the distance between a vocalist and a

microphone changes, variations in signal level occur.

Start with the 160X adjusted for low compression

(around

2:1)

and adjust the THRESHOLD control

for optimum

results,

then increase

RATIO

necessary.

4.2 SMOOTHING VARIATIONS IN

INSTRUMENT LEVEL

achieve

a smoother

electric-bass

sound,

compress the instrument's output with a ratio of

about 4: 1. Compression lessens the loudness

variations among the strings and increases the

sustain. Other instruments, such as horns, vary in

loudness depending on the note being played,and

benefit similarly.

NOTE: When compressing a stereo program with a

pair of 160Xs, the factors affecting a compression

curve, and the actual compression and threshold

settings, are like those previously covered with

reference to single channels of program material.

However, it will generally be found that large

amounts of compression are more audible in a

mixed stereo program than they might be on the

separate tracks that were mixed to create the

program.

4.3 RAISING A SIGNAL OUT OF A MIX

Since reducing dynamic range increases the

average

signal level and meter readings by a small

amount, a single track can be raised out of a mix

by boosting its level slightly and applying com-

pression. It is also possible to separate certain

vocals or instruments from a mono

program

already mixed by following the procedure in

Section 4.6.1.

4.4 PREVENTING TAPE SATURATION

With programs of widely varying levels, com•

pression

can prevent recording levels from satur•

ating

tape

tracks (see also Section 4. 7

.1).

4.5

SPEAKER

PROTECTION

Compressors are frequently used to prevent

excessive program levels from damaging drivers

sound-reinforcement system. Limiting also

benefits intelligibility by allowing low-level input

signals

to be reproduced through·the system at

higher volume.

In a musical performance, this

provides

additional intimacy as the vocalist's

whispers are heard clearly at each seat in the house.

The

Over

Easy curve utilized by the 160X permits

a very high

amount of compression (10:1 or

greater)

to be used in many situations. Vocalists

and musicians don't get the sense of being

"choked

back", but high average levels can be maintained

without the speaker damage which would

norn,ally

occur

due to excessive heat buildup

in the drivers.

In circumstances where the 160X is expected

cause no change

in gain unless an emergency

arises (wildly excessive levels) some operators

set the RATIO to•:

1, the THRESHOLD to the

highest permissible level, and operate the unit in

hard-knee mode. (In hard-knee mode, the 160X

will perform in the manner of

Its

predecessor, the

16Q.) As

general rule, the comprnaors should be

as clou

th11 •mplifi11r, • p0$$ibl•

in the signal

chain. If the 180X Is placed before the EQ, for

example,

potentially damaging boost in EQ

won't bG seen by

the

unit and the speakers may

be damaged.

(See

Section

4.8.2.)

For maximum

sound-pressure levels, large sound-reinforcement

systems frequently

use a separate

compressor on

each output of the electronic crossover(s). For a

stereo sounckeinforcement system, stereo

strapping

cabin

should be run between the 160Xs

in each band (low-low, .mid-mid,.etc) •

•

4.8 INFINITY+T~ COMPRESSION

It has been noted that with a full-scale

Infinity+ setting of-1.1, a 1 dB

decreasa

of input level above THRESHOLD causes a

1 dB incmnt1 of output level. It can

be seen

how this differs from the full counter-

clockwise setting of 1

1, where the transfer

function is linear (e.g., a 1 dB

increas11

of input

level causes a 1 dB

decrease

of output level).

A total dynamic reversal of the entire program

being processed will not occur unless the

THRESHOLD is

set

very low (e.g., -40 dBm)

and all the program material falls above the

threshold level. More often, some of the

program input will

below threshold, and

will therefore have normal dynamics - that

is, the output level will change linearly with

changes of input level. As the input level rises

above threshold, however, the output level will

begin to decrease. The audible results will differ

with

different types of program material and

different settings. With instruments havina_fast

attack times, such

as a

picked guitar,

harpsichord,

or a drum, a low threshold will all but eliminate

the attack transient. Interesting effects can be

obtained by setting a moderate threshold with

instruments with a slower attack, such as wind

instruments or bowed strings; the level will build

normally up to the threshold, then begin going

lower, the output will become very quiet as the

instrument is generating its loudest sound, perhaps

quieter than when the note first began.

4.7 USING THE DETECTOR INPUT

4.7. 1

Detector EQ For Signal Enchancement

possible to separate certain vocals and

instruments from a mix by frequency-weighted

compression. With an equalizer ioserted ahead of

the detector input (but not in the audio path), the

equalization settings do not shift the timbre or

frequency response of

the

audio signal. They

merely alter the threshold response of the com-