ACT apricot - Noise Generation

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SOUND

GENERATION

NOTE:

Tone

generator 1 is

normally

assigned

to

produce

the

bell

tone.

The

frequency of

the

bell

tone

(800Hz) is

set

up during

initialisation

and

then

activated

and

inhibited

using

the

level

control

byte.

Noise

Generation

The

noise generator is able to

function

in

either

one of

two

modes.

The

first

mode

produces

"white

noise"

and

the

second

mode

produces "periodic noise".

The

noise source for

the

generator is based

on

a feedback

shift register

network

with

the

shift rate

determined

by a

reference frequency.

The

reference frequency

can

be

either

one of

three

preset

frequencies, or be

determined

by

the

audio signal frequency

output

from

tone

generator 3.

The

choice of

mode

and

reference frequency for

the

noise

source is

determined

by a single noise control byte.

Two

bits of

the

noise

control

byte

define

the

reference frequency

and

one

bit

defines

the

mode.

Three

of

the

remaining

bits

are

used

to

select

the

noise

generator control register (as

defined by

the

register

selection

table

in

the

tone

generator

section above),

and

the

remaining

bit

signifies

that

the

byte

contains register

selection

bits.

The

format of

the

noise

control

byte

is

as follows.

D7

DO

11

I

R21

Rl

I

RO

I x I

FB

INFIINFO

I NOISE

CONTROL

BYTE

I I

III

~selects

reference

Selects

mode

Immaterial

........

----

Register

selection

i-...-

____

Byte

differentiation

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Other manuals for ACT apricot

Service Manual305 pages