Marantz 5220 User Manual download pdf (Page 90)

Experimenter's

Corner

PERCUSSION

INSTRUMENT

SYNTHESIZER

THANKS

John

Simonton,

and

Don Lancaster,

this

magazine

has

featured

articles

virtually

every

as-

pect

of electronic music

over the

past

several years.

Recently

the

electronic music

bug

bit me.

Having

tinkered

with

several

the

basic

circuits, I'm

convinced

that

voicing

circuits are

far

the

most

challenging

-and

the

most fun.

course, they

can

very

difficult

implement,

but the

successful

elec-

tronic

synthesis

the

unique

"voice"

or timbre

of a particular

musical in-

strument

quite rewarding.

Percussion

instruments

are among

the

simplest

simulate,

let's

jump

into

electronic

music

by putting

a per-

By Forrest

M. Mims

cussion

synthesizer together.

Since

percussion instruments include

the

bell, gong,

cymbals, triangle,

xylophone,

tambourine,

and

drum,

successful percussion

synthesizer

has

lots

of uses!

The first

step

of a successful design

to study the waveforms

produced by

the instrument

be synthesized. If

you're new to

electronic music,

prepared

for

a surprise! "Ordinary"

musical instruments

produce

some

very

extraordinary waveforms. To

make matters

even worse, the

amplitude

(signal strength)

the

waveform

during

the

first

100 mil-

liseconds

or so

usually irregular

and

often unique. For

example, the

cello

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has

a gradual,

slow amplitude rise

time,

but

the

tuba has a fast rise time in

the

form

a high -amplitude

spike fol-

lowed

by the remainder

of the

sound

"envelope." See Don Lancaster's

arti-

cle "Imitating

Musical Instruments

with

Synthesized

Sound" (POPULAR

ELECTRONICS,

August

1975,

p. 37)

for

information

on the

sound en-

velopes

these

and other

nonper-

cussion

instruments.

Fortunately,

percussion instru-

ments

produce

fairly

orderly sound

envelope. Figure

1 is a somewhat

simplified version

the waveform

AMPLIT,.IDE

ATTACK

DECAY

Fig. I. in 1)('r(lt.tisir(' 7('Qr'efOrin,

ris('

1(r.tit Had decay

.,tore.

Tihr

produced

by a

typical percussion

in-

strument. The waveform

consists of

strong,

fast rise

-time

"attack"

fol-

lowed

by a gradual

"decay."

In the

case of a bell, the

attack

is the initial

high -amplitude

sound

produced

when the

bell

struck by

its

clapper.

The

decay is the

ringing

sound rep-

resentative

the

bell's

natural reso-

nant frequency.

Now

that we've defined the

fre-

quency

and amplitude

relationships

the

sounds we

wish to

simulate,

can start designing a circuit.

Fortu-

nately,

our

task

easy because "ring-

ing," the

effect we

want to

simulate,

a common and even

pesky

problem

many

electronic circuits!

An active notch

filter happens

make

an excellent

ringing

circuit

since

it has

natural resonance fre-

quency and can be adjusted

a criti-

cal

point where oscillation can be ex-

ternally

stimulated

and internally

damped.

you

may know, an active

filter

uses transistors or, better, one or

op amps

to simulate a conven-

tional filter. The

active

filter is

superior

a passive

filter

since

it has

internal

gain

which replaces the

losses

pas-

sive

filters

and since

can

be made

with a

very high input impedance (very

desirable) and a

low

output

imped-

ance (also

very good).

POPULAR

ELECTRONICS

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