_SNDRAW
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The _SNDRAW statement plays sound wave sample frequencies created by a program.
Syntax
- _SNDRAW leftSample[, rightSample][, pipeHandle&]
Parameters
- 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.
Description
- 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.
Examples
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 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 _SNDRAWDONE 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))).
Example 2: A simple ringing bell tone that tapers off.
t = 0 tmp$ = "Sample = ##.##### Time = ##.#####" LOCATE 1, 60: PRINT "Rate:"; _SNDRATE DO 'queue some sound DO WHILE _SNDRAWLEN < 0.2 'you may wish to adjust this sample = SIN(t * 440 * ATN(1) * 8) '440Hz sine wave (t * 440 * 2π) sample = sample * EXP(-t * 3) 'fade out eliminates clicks after sound _SNDRAW sample t = t + 1 / _SNDRATE 'sound card sample frequency determines time LOOP 'do other stuff, but it may interrupt sound LOCATE 1, 1: PRINT USING tmp$; sample; t LOOP WHILE t < 3.0 'play for 3 seconds _SNDRAWDONE DO WHILE _SNDRAWLEN > 0 'Finish any left over queued sound! LOOP END |
Example 3: Routine uses _SNDRAW to display and play 12 notes from octaves 1 through 9.
DIM SHARED rate& rate& = _SNDRATE DO PRINT "Enter the octave 1 to 8 (0 quits!):"; oct% = VAL(INPUT$(1)): PRINT oct% IF oct% = 0 THEN EXIT DO octave = oct% - 4 '440 is in the 4th octave, 9th note COLOR oct% + 1 PRINT USING "Octave: ##"; oct% FOR Note = 0 TO 11 'notes C to B fq = FreQ(octave, Note, note$) PRINT USING "#####.## \\"; fq, note$ PlaySound fq IF INKEY$ > "" THEN EXIT DO NEXT LOOP END 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 WHILE SndLoop! < rate& _SNDRAW SIN((2 * 4 * ATN(1) * SndLoop! / rate&) * frq!) * EXP(-(SndLoop! / rate&) * 3) SndLoop! = SndLoop! + 1 LOOP _SNDRAWDONE DO: LOOP WHILE _SNDRAWLEN 'flush the sound playing buffer END SUB |
See also