dbx 165 Manuel d'instruction - Page 17

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Sub

armonic

A sub-multiple of the fundamental frequency. For example,

a wave

the frequency of which is half the fundamental frequency

of another

wave

is called the second sub harmonic of that

wave.

Sub

Woofer

A loudspeaker made specifically to reproduce the lowest of

audio frequencies, usually between 20Hz and 1 OOHz.

Sy nthesizer

An ELEC

RONIC MUSIC SYNTHESIZER

is an aud io

processor that has a bui lt-in sound generator (oscillator!,

and

that alters the envelope of the sound w ith voltag

contro

circuitry. Synthesizers can produce familiar sounds and serve as

musical instruments, or they can create many un ique sounds

and effects of their own.

A SUB HARMONIC SYN

ESIZER is a device which is not

used to create music, but to enhance an existing audio program.

In the case of the dbx Model 100, the unit creates a new signal

that corresponds to the volume of the input signal, but is at

the frequency of the input signal.

T ape Satu

ratio

There is a ·maximum amount of energy that can be recorded on

any given type of magnetic tape. When a recorder "tries" to record

more energy, the signals become distorted, but are not recorded at

any higher levels. This phenomenon is called tape saturation

because the magnetic ox ide particles of the tape are literally

saturated with energy and cannot accept any more magnetization.

.H.D. (Total Harmon ic

sto

t ion) (See "Harmonic

Distortion")

Threshold

the level at which a compressor c,r limiter ceases to

have

inear gain, and begins to perform

its

gain-changing function

(i.e., where the output level no

longer

rises and falls in direct

proportion

the

input

level). In most systems, the threshold is a

point above which the level changes, although there are compressors

that

raise

signal levels below a threshold point. Some compander-

type noise

reduction

systems, such as Do lby~•

have upper andl

lower

threshold between which the gain changes; these systems

require carefu

level calibration for proper encode/decode perfor-

mance. dbx noise reduction systems have no threshold at which

compress ion or expansion factors change, so level calibration is

not critical.

INPUT

OUTPUT

120

ComPfenion

Comp,en1on

Uim itin;;il

- - - -

Thres:hold

- -

---

acking Accu racy

Tracking

refers

to the ability of one circuit to "follow"

the

changes of another circuit. When two volume contro ls are adjusted

*•oolby'

a trademark of Dolby® Laboratories, Inc.

Manufactured

under one or

more of

the

following

U.S. patents:

,681

,618

;

3,714,462;

3,789,143;

4,101,849;

4,097,767.

Other

patents pending.

in exactly the same way, the corresponding "sameness" of the

output levels can be expressed as the tracking accuracy of the

controls.

he level detection circuitry

in a dbx encoder senses the signal

level, changes the

gai

n, and creates an encoded signal. The corre-

sponding "sameness" of the original signal and the encoded/

decoded signal can be expressed as the tracking accurac'y of the

noise reduction system. (dbx systems are non-critical for the

operator, and are built to close tolerances, so that

racking

accuracy is excellent, even if the encoder and decoder are in

different pieces of db

equipment.I

ansitio

n Level

(See Level Match)

When a circuit has uniform compression or expansion through-

out its full dynamic range,

here must be some level which passes

through the unit without

being raised or lowered

here gain is

unity). This unity gain level is the transition level or transition point.

The transition point is a "window"

1 dB wide, in a dbx encoder

(compressor). all signals above the

transition

point are decreased in

level, and all signals below the point are increased in level. Con-

versely, in a dbx decoder (expander), all signals above the

transition point are increased

level, and all signals belo

the

point are decreased in level. The transition level

simi lar to a

"threshold,"

except it does not refer to a point at which

compression or expansion factors change.

Triamplifi ed

Similar to biamplified.

A sound system

here a passive cross-

over network creates three frequ ency ranges, and feeds three power

ampli

iers: one for bass,

one

for mid, and one for high frequencies.

he amplifiers are connected directly to the woofers, midrange

drivers and tweeters without a passive, high-level crossover network.

Tun er

A unit which receives radio broadcasts and converts them

into audio freq uency signals. May be part of a receiver.

VCA (Vo lta

ge Controll ed

plifi er)

Traditionally,

ampl ifiers have been designed to increase

signal

levels (to provide gain). If an amplifier were required to decrease

the level (to attenuate), it could become unstab le, and might even

oscillate.

he gain (amount of amplification)

in these traditional

amplifiers would be adjusted by one of three methods (1) attenuat-

ing the audio signal fed to the input of the amplifier, (2) attenuating

the audio output of

the

amplifier, or (3) changing the negative feed-

back (feeding more or less

signal

from the output back to the

input,

but in reversed polarity).

The VCA is a special type of amp lifier that can be used to

increase or decrease levels over a wide dynamic range. Instead of

using signal attenuation or negative feedback, the gain (or loss) is

adjusted by means pf an external de control voltage. dbx has a

unique, patented VCA design that has extremely low noise and

very wide dynamic range;·'the dbx VCA is the heart of dbx noise

reduction equipment.

Woofer

A loudspeaker which reproduces only low frequencies.

9805C-600127