SOUND
This page was last modified 15:24, 25 August 2018 by Mars2000you. Based on work by Gdx and Rderooy and others.

Contents

Effect

Writes a value in a sound register of PSG.

Sound registers 14 and 15 and the two highest bits of register 7 are not accessible with this command.

Syntax

SOUND <register number>,<value>

Parameters

<register number> is the register number (0-13) to write. It can be a variable or an expression.

<value> is a value whose limits depend on the register to write (see Registers Description below). It can be a variable or an expression.

Recommendation for maximum compatibility: when you write register 7 it is good habit to set bit 7 and reset bit 6 although these potentially harmful values should not end up to PSG in any case. That's why only the values 128 to 191 are mentioned below for this register.

Registers Description

Register Description Values
0 Least signifiant bits of channel A frequency 0~255
1 Most significant bits of channel A frequency 0~15
2 Least significant bits of channel B frequency 0~255
3 Most significant bits of channel B frequency 0~15
4 Least significant bits of channel C frequency 0~255
5 Most significant bits of channel C frequency 0~15
6 Noise generator frequency 0~31
7 Mixer setting 128~191
8 Volume of channel A 0~16
9 Volume of channel B 0~16
10 Volume of channel C 0~16
11 Least significant bits of envelope period 0~255
12 Most significant bits of envelope period 0~255
13 Envelope shape 0~15

About registers 0 to 5:

The value indicating the frequency to be produced on a channel is 12 bits. It is therefore divided into two registers. The value to be written is obtained using the following expression:

Value = Fi / (16 x Fn)

Fi = Internal frequency of PSG (1789772.5 Hz on MSX)
Fn = Frequency of the sound to be produced (varies between 27 and 111960 Hz)

For simplicity, here is a table of musical notes obtained according to the value indicated in the registers 0~1, 2~3 or 4~5:

Octave
Note 1 2 3 4 5 6 7 8
C D5Dh 6AFh 357h 1ACh 0D6h 06Bh 035h 01Bh
C# C9Ch 64Eh 327h 194h 0CAh 065h 032h 019h
D BE7h 5F4h 2FAh 17Dh 0BEh 05Fh 030h 018h
D# B3Ch 59Eh 2CFh 168h 0B4h 05Ah 02Dh 016h
E A9Bh 54Eh 2A7h 153h 0AAh 055h 02Ah 015h
F A02h 501h 281h 140h 0A0h 050h 028h 014h
F# 973h 4BAh 25Dh 12Eh 097h 04Ch 026h 013h
G 8EBh 476h 23Bh 11Dh 08Fh 047h 024h 012h
G# 86Bh 436h 21Bh 10Dh 087h 043h 022h 011h
A 7F2h 3F9h 1FDh 0FEh* 07Fh 040h 020h 010h
A# 780h 3C0h 1E0h 0F0h 078h 03Ch 01Eh 00Fh
B 714h 38Ah 1C5h 0E3h 071h 039h 01Ch 00Eh

(*) 0FEh is the note produced by a tuning fork.


About register 6:

The value indicating the frequency of the white noise generator is 5 bits. The value to be written is obtained using the following formula:

Value = Fi / (16 x Fb)

Fi = Internal frequency of PSG (1789772.5 Hz on MSX)
Fb = Noise frequency master to be produced (varies between 27 and 3608 Hz)


About register 7:

This register is used to activate or deactivate the tone generator as well as the noise generator. The format of the value is as follows:

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
PSG I/O ports Disabling noise Disabling tone
B=1 A=0 channel C channel B channel A channel C channel B channel A

Bits 7 and 6 serves to specify the direction of PSG I/O ports. Always set bit 7 and reset bit 6. Otherwise some devices connected to the joystick ports may malfunction.


About register 8 to 10:

The format of these registers is as follows:

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
V/A Volume / Amplitude of the channel

Reset bit 4 (V/A) to adjust the volume of the corresponding channel, if set the volume will vary in proportion to the envelope shape defined by register 13.


About register 11 to 13:

The registers 11 and 12 control the envelope period. The value is on 16 bits (0~65535). It is calculated with the following expression:

Value = Fi / (16 x T)

Fi = Internal frequency of PSG (1789772.5 Hz on MSX)
T = Period of the envelope (in μs)

The register 13 defines the envelope shape. Here are the possible shapes:

  • 0~3 \_______
  • 4~7 /_______
  • 8 \\\\\\\\
  • 9 \_______
  • 10 \/\/\/\/
  • 11 \ ̄ ̄ ̄ ̄ ̄ ̄ ̄
  • 12 ////////
  • 13 / ̄ ̄ ̄ ̄ ̄ ̄ ̄
  • 14 /\/\/\/\
  • 15 /_______

Example

5 ' Initializes the sound registers of the PSG
10 FOR R=0 TO 13
20 IF R=7 THEN SOUND R,&B10111111 ELSE SOUND R,0
30 NEXT
40 ' Plays the note C on channel A with a volume of 12
50 SOUND 0,&hAC ' 8 least significant bits of frequency on channel A
60 SOUND 1,1 ' 4 most significant bits of frequency on channel A
70 SOUND 8,&b1100 ' Sets the volume to 12 on channel A
80 SOUND 7,&b10111110 ' Activates the sound generator on channel A

Same example in decimal mode for the values:

5 ' Initializes the sound registers of the PSG
10 FOR R=0 TO 13
20 IF R=7 THEN SOUND R,191 ELSE SOUND R,0
30 NEXT
40 ' Plays the note C on channel A with a volume of 12
50 SOUND 0,172 ' 8 least significant bits of frequency on channel A
60 SOUND 1,1 ' 4 most significant bits of frequency on channel A
70 SOUND 8,12 ' Sets the volume to 12 on channel A
80 SOUND 7,190 ' Activates the sound generator on channel A

Related to

BEEP, PLAY, PLAY()

Compatibility

MSX-BASIC 1.0 or higher

Links