Trigger a sound on Amstrad CPC | Pattern Library

Give an accepted action a sound. The same caller changes its picture and triggers this effect; a second version performs the action with the trigger removed. Listen to both.

Working effect

Trigger omitted

Take the effect

The reusable effect

sound.bas

2000 SOUND 1,100,10,15
2010 RETURN

SOUND 1,100,10,15 submits a channel-A note to the firmware sound system. This routine returns after submission, subject to the firmware queue being able to accept the command. Firmware owns subsequent playback.

Copy the 2000-range subroutine and call GOSUB 2000 when the game accepts an action. Keep its global scratch variables and any DATA/setup lines with it. A sound call is a consequence of an action, not a substitute for input validation.

Change it and recognise a mistake

Change the SOUND period, duration or volume operands. Adding envelopes changes the duration contract; filling the firmware queue can make submission wait.

The omitted-trigger control still accepts the action but fails the same audio guard as the working caller. Keyboard clicks or other machine output are not enough: the BASIC checks compare against a separate rejected-command recording.

Deliberately omitted sound trigger

no-sound.bas

10 MEMORY 39999:MODE 1
20 N=0:POKE 40000,0
30 CLS:PRINT "TURN";N
31 GOSUB 1000
40 GOSUB 3000
50 IF A$="GO" THEN N=(N+1) AND 255
60 POKE 40000,N
70 GOTO 30
1000 PRINT "XXX"
1010 PRINT "X X"
1020 PRINT "XXX"
1030 RETURN
2000 SOUND 1,100,10,15
2010 RETURN
3000 INPUT A$
3010 RETURN

The working implementation above repairs that omission. If an effect instead drones on, check the mute/service path and that its state is initialised. Servicing twice makes a counted effect shorter; servicing only after input can leave it running while the player waits. Those are lifecycle decisions to test when adapting it.

Run the caller

Enter the complete demo.bas in Amstrad CPC BASIC and RUN. Submit GO, then Return. One accepted command advances the displayed turn; another gives two.

Amstrad CPC native caller after accepted input. — Captured from the running caller in the configuration below.

Where setup, trigger and service belong

demo.bas

10 MEMORY 39999:MODE 1
20 N=0:POKE 40000,0
30 CLS:PRINT "TURN";N
31 GOSUB 1000
40 GOSUB 3000
50 IF A$="GO" THEN N=(N+1) AND 255:GOSUB 2000
60 POKE 40000,N
70 GOTO 30
1000 PRINT "XXX"
1010 PRINT "X X"
1020 PRINT "XXX"
1030 RETURN
2000 SOUND 1,100,10,15
2010 RETURN
3000 INPUT A$
3010 RETURN

Compare blocking, serviced and queued sound when choosing the next step.

Verification and sources

Target: CPC464 PAL, Locomotive BASIC, MODE 1. These callers were executed with released Emu198x 0.44.1; assembly uses Asm198x 0.0.71. The sample folder contains reproduction instructions and retained observations. The independent checker binds source, native captures and actual output; its rejection tests exercise wrong state, missing files and false audio claims.

This qualifies the named emulator/firmware path. Pitch accuracy, original hardware and other peripherals require their own observations.

Amstrad, CPC464 User Instructions: Locomotive BASIC entries INPUT, GOSUB, RETURN and SOUND, including channel/queue behaviour.