Multimoog Musical Instrument Wartungshandbuch PDF herunterladen (Seite 31)

EXERCISE

7:

MODIFYING

LOUDNESS

BY

CONTROLLING

THE

VCA

OCX

■Mat

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1.

Place

BYPASS

switch

to

ON

position.

You

should

hear

sound

continuously,

since

the

voltage

controlled

amplifier

(VCA)

is

being

held

completely

open

("bypassed").

2.

Return

BYPASS

switch

to

OFF.

Depress

any

key,

then

release.

The

sound

is

articulated

with

nearly

immediate

attack

and

release.

3.

Notice

that

the

ATTACK

and

RELEASE

controls

of

the

LOUDNESS

CONTOUR

are

set

for

immediate

attack

and

release.

Play

keyboard

and

note

that

the

sound

is

articulated

with

immediate

attack

and

release

(beginning

and

end).

4.

Vary

the

ATTACK

control

in

the

LOUDNESS

CONTOUR

slightly.

Play

keyboard.

The

initial

part

of

the

sound,

or

attack

time,

is

increased

as

you

move

the

control

clockwise.

5.

Vary

the

RELEASE

control

in

the

LOUDNESS

CONTOUR.

Notice

that

the

timing

of

the

final

portion,

or

release of

the

sound

is

increased

as

you

move

the

control

clockwise.

(END

EXERCISE)

When

the

BYPASS

switch

is

in

its

normal

OFF

position,

the

LOUDNESS

CONTOUR

section

is

connected

to

the

control

input

of

the

voltage

controlled

amplifier

(VCA).

The

LOUDNESS

CONTOUR

creates

a

voltage

"contour"

(sometimes

called

"envelope")

which

opens

and

closes

the

VCA,

shaping

the

loudness

of

any

sound

passing

through

the

VCA.

Use

of

the

LOUDNESS

CONTOUR

section

to

control

the

VCA

doesn't

"turn

on"

any

of

the

sound

sources—they

are always

potentially

available

for

use.

The

sound

source

in

use

is

always

present

at

the

audio

input

of

the

VCA;

the

VCA

modifies

the

sound

source

by

amplifying

it.

The

amount

of

this

amplification

is

controlled

by

the

LOUDNESS

CONTOUR

section

when

it

generates

a

signal

that

"contours,"

or

increases

and

decreases

the

gain

(amplification)

of

the

VCA.

FILTER

SECTION

A

filter

modifies

sound

the

way

the

name

implies—it

removes

a

portion

of

the

sound.

The

Multimoog

features

the

patented

Moog™

wide

range

lowpass

resonant

filter.

This

unique

filter

plays

a role

in

creating

the

distinctive

and

recognizable

"Moog

Sound"

that

has

become

popular.

The

Multimoog's

FILTER

section

is

a

lowpass

filter;

this

filter

acts

to

pass

the lows

of

a

sound

and

reject

the

highs.

The

FILTER

section

attenuates,

or

"cuts

off"

the

higher

frequency

components—those

which

lie

above

the

adjustable

"cutoff

frequency,"

and

passes

the

lower

frequency

components

of

the

signal

passing

through.

The

CUTOFF

control

sets

this

cutoff

frequency.

The

cutoff

frequency

is

lowered

as

the

CUTOFF

control

is

moved

counterclockwise;

the

lower

the

cutoff

frequency,

the

fewer

highs

a signal

will

have

after

passing

through

the

filter.

A

waveshape

is

rounded

and

smoothed

as

the

CUTOFF

control

is

moved

counterclockwise.

When

the

cutoff

frequency

is

so

low

it

approaches

the

fundamental

frequency

of

the

waveshape,

almost

all

of

the

upper

harmonics

are

cut

off

and

the

signal

approximates

a

sine

waveshape

(pure

tone

with

no

harmonics).

If

the

CUTOFF

control

is

set

to

cause

a

very

low

cutoff

frequency,

all

sound

may

be

cut

off

and

silence

will

result.

The

following

Exercise

illustrates

FILTER

section

features:

36

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