_SNDRAW - mkilgore/QB64pe GitHub Wiki

The _SNDRAW statement plays sound wave sample frequencies created by a program.

_SNDRAW leftSample[,][,]

• The leftSample and rightSample value(s) can be any SINGLE or DOUBLE literal or variable frequency value from -1.0 to 1.0.
• The pipeHandle& parameter refers to the sound pipe opened using _SNDOPENRAW.

• Specifying pipeHandle& allows sound to be played through two or more channels at the same time (version 1.000 and up).
• If only leftSample value is used, the sound will come out of both speakers.
• Using _SNDRAW will pause any currently playing music.
• _SNDRAW is designed for continuous play. It will not produce any sound until a significant number of samples have been queued. No sound is played if only a few samples are queued.
• Ensure that _SNDRAWLEN is comfortably above 0 (until you've actually finished playing sound). If you are getting occasional unintended random clicks, this generally means that _SNDRAWLEN has dropped to 0.
• _SNDRAW is not intended to queue up many minutes worth of sound. It will probably work but will chew up a lot of memory (and if it gets swapped to disk, your sound could be interrupted abruptly).
• _SNDRATE determines how many samples are played per second, but timing is done by the sound card, not your program.
• Do not attempt to use _TIMER or _DELAY or _LIMIT to control the timing of _SNDRAW. You may use them for delays or to limit your program's CPU usage, but how much to queue should only be based on the _SNDRAWLEN.

Example 1: Sound using a sine wave with _SNDRAW Amplitude * SIN(8 * ATN(1) * Duration * (Frequency / _SNDRATE))

FREQ = 400                             'any frequency desired from 36 to 10,000
Pi2 = 8 * ATN(1)                       '2 * pi 
Amplitude = .3                         'amplitude of the signal from -1.0 to 1.0
SampleRate = _SNDRATE                  'sets the sample rate
FRate = FREQ / SampleRate'
FOR...NEXT Duration = 0 TO 5 * SampleRate     'play 5 seconds
        _SNDRAW Amplitude * SIN(Pi2 * Duration * FRate)            'sine wave
       '_SNDRAW Amplitude * SGN(SIN(Pi2 * Duration * FRate))       'square wave
NEXT
DO: LOOP WHILE _SNDRAWLEN
END '' ''

Explanation: The loop Duration is determined by the number of seconds times the _SNDRATE number of samples per second. Square waves can use the same formula with Amplitude * SGN(SIN(8 * ATN(1) * Duration * (Frequency/_SNDRATE))).

  'do other stuff, but it may interrupt sound
  LOCATE 1, 1: PRINT USING tmp$; sample; t
LOOP WHILE t < 3.0                      'play for 3 seconds

DO WHILE _SNDRAWLEN > 0                 'Finish any left over queued sound!
LOOP
END '' ''

Example 3: Routine uses _SNDRAW to display and play 12 notes from octaves 1 through 9.

FUNCTION FreQ (octave, note, note$)
FreQ = 440 * 2 ^ (octave + (note + 3) / 12 - 1) '* 12 note octave starts at C (3 notes up)
note$ = MID$("C C#D D#E F F#G G#A A#B ", note * 2 + 1, 2)
END FUNCTION

SUB PlaySound (frq!)    ' plays sine wave fading in and out
SndLoop! = 0
DO...LOOP WHILE SndLoop! < rate&
  _SNDRAW SIN((2 * 4 * ATN(1) * SndLoop! / rate&) * frq!) * EXP(-(SndLoop! / rate&) * 3)
  SndLoop! = SndLoop! + 1
LOOP
DO: LOOP WHILE _SNDRAWLEN   'flush the sound playing buffer
END SUB '' ''

• _SNDRATE, _SNDRAWLEN
• _SNDOPENRAW, _SNDRAWDONE
• _SNDOPEN
• PLAY, BEEP
• Music Frequency table in SOUND.
• DTMF Phone Demo