BBC BASIC Programmers' Reference

by Richard Russell, March 2014

The code below implements a QBASIC-compatible PLAY command, which allows you to play simple tunes; it makes use of the BBC BASIC SOUND and ENVELOPE statements available in LBB. The example tune is from Beethoven's Ode to Joy:

    CALL QBplay "L8eefggfedccdeL6eL16dL4d"
    CALL QBplay "L8eefggfedccdeL6dL16cL4c"
    CALL QBplay "L8ddecdL16efL8ecdL16efL8edcdL4<g>"
    CALL QBplay "L8eefggfedccdeL6dL16cL4c"
    END

SUB QBplay play$
    GLOBAL QBoct, QBdur, QBtem, QBenv
    IF QBoct = 0 THEN QBoct = 3
    IF QBdur = 0 THEN QBdur = 4
    IF QBtem = 0 THEN QBtem = 90
    IF QBenv = 0 THEN
      QBenv = 2
      !ENVELOPE 1,1,0,0,0,0,0,0,127,-1,-1,-1,100,0
      !ENVELOPE 2,1,0,0,0,0,0,0,127,-2,-4,-4,100,0
      !ENVELOPE 3,1,0,0,0,0,0,0,127,-4,-8,-8,100,0
    END IF
    play$ = upper$(play$)
    DO
      cmd$ = LEFT$(play$,1)
      play$ = MID$(play$,2)
      e = INSTR(play$,"E")
      IF e THEN q = VAL(LEFT$(play$,e-1)) ELSE q = VAL(play$)
      SELECT CASE cmd$
        CASE "L": QBdur = q
        CASE "T": QBtem = q
        CASE "O": QBoct = q
        CASE "<": IF QBoct > 0 THEN QBoct = QBoct - 1
        CASE ">": IF QBoct < 6 THEN QBoct = QBoct + 1
        CASE "N":
          IF q THEN
            !SOUND 1, QBenv, q*4-44, 6000/QBdur/QBtem
          ELSE
            !SOUND 1, QBenv, 0, 6000/QBdur/QBtem
          END IF
        CASE "P":
          !SOUND 1, QBenv, 0, 6000/q/QBtem
        CASE "M":
        SELECT CASE LEFT$(play$,1)
          CASE "L": QBenv = 1
          CASE "N": QBenv = 2
          CASE "S": QBenv = 3
        END SELECT
        play$ = MID$(play$,2)
        CASE "A","B","C","D","E","F","G":
        IF q THEN d = 6000/q/QBtem ELSE d = 6000/QBdur/QBtem
        q = 8 * INSTR("CDEFGAB", cmd$) - 8 : IF q >= 24 THEN q = q - 4
        IF LEFT$(play$,1) = "#" THEN play$ = MID$(play$,2) : q = q + 4
        IF LEFT$(play$,1) = "+" THEN play$ = MID$(play$,2) : q = q + 4
        IF LEFT$(play$,1) = "-" THEN play$ = MID$(play$,2) : q = q - 4
        IF LEFT$(play$,1) = "." THEN play$ = MID$(play$,2) : d = d*3/2
        IF LEFT$(play$,1) = "." THEN play$ = MID$(play$,2) : d = d*7/6
        q = QBoct*48 + q - 44
        WHILE q <= 0  : q = q + 48 : WEND
        WHILE q > 255 : q = q - 48 : WEND
        !SOUND 1, QBenv, q, d+0.5
      END SELECT
    LOOP UNTIL play$ = ""
END SUB