Musical scale: Difference between revisions

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As a low level stack language Forth programming methodology prefers short simple definitions that extend the language in the direction that allows you to solve the problem. The creation of application specific language is common in Forth.

This demonstration code uses the PC speaker to generate musical tones. A simple device driver is created for hardware control via PORT I/O. A set of primitive operations are created to control the on:off times of the sounds. Then a small MUSIC language is created to create notes of different types. Finally 2 scales are created using "crotcheted notes" as they are called. We chose 1/8 notes. For fun we added the ability to change the expression of the notes using Italian musical terms.

<lang>~~\ play a scale~~

<lang>HEX

HEX

\ PC speaker hardware control (requires giveio or DOSBOX for windows operation)

042 constant fctrl 061 constant sctrl

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: silence ( -- ) sctrl pc@ smask and 01 or sctrl pc! ;

HEX

: tone ( divisor -- )

?dup \ check for non-zero input

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8 rshift fctrl pc! \ load high byte

sing

else silence

then ;

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variable off_time

variable feel \ controls the on/off time ratio

⚫

4000 60 m* 2constant timebase \ 1 whole note=4000 ms @ 60 Beats/min

60 value tempo

⚫

4000 tempo um* 2constant timebase \ 1 whole note=4000 ms @ 60 Beats/min

⚫

: bpm>ms ( bpm -- ms) timebase rot um/mod nip ; \ convert beats per minute to milliseconds

: wholenote ( -- ms ) tempo bpm>ms ; \ using tempo set the BPM

⚫

: bpm>ms ( bpm -- ms) timebase rot um/mod nip ; \ convert beats per minute to milliseconds

⚫

: ~~play~~ ( ~~divisor~~ -- ) tone on_time @ ms silence off_time @ ms ;

: ~~rest~~ ( -- ) ~~note~~ ms ;

: wholenote ( -- ms ) tempo bpm>ms ; \ using tempo set the BPM

: play ( divisor -- )

⚫

tone on_time @ ms silence off_time @ ms ;

: expression ( ms n --) \ adjust the on:off ratio using n

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off_time ! on_time ! ; \ store times in variables

: note ( -- ms ) on_time @ off_time @ + ; \ returns duration of current note

: duration! ( ms -- ) feel @ expression ;

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MUSIC DEFINITIONS

: BPM ( bpm -- ) \ set tempo in beats per minute

to tempo

~~tempo bpm>ms~~ duration! ;

wholenote duration! ;

: legato wholenote 3 % feel ! ;

: legato wholenote 2 feel ! ;

: staccatto wholenote 25 % feel ! ;

: staccatto wholenote 8 % feel ! ;

: Marcato wholenote 10 % feel ! ;

: Marcato wholenote 3 % feel ! ;

: 1/1 wholenote duration! ;

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: 1/16 1/8 note 50% duration! ;

: 1/32 1/16 note 50% duration! ;

: rest note ms ;

\ note object creator

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: Chromatic 1/8 C3 C#3 D3 D#3 E3 F3 F#3 G3 G#3 A3 A#3 B3 C4 ;

</lang>

=== Test at the Console ===

<pre>music ok

120 bpm legato cmajor ok

200 bpm marcato chromatic ok

72 BPM legato c3 eb3 g3 c4 ok

</pre>

=={{header|J}}==