_SNDRAWBATCH
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The _SNDRAWBATCH statement plays a batch of sound wave sample frequencies created by a program.
Syntax
- _SNDRAWBATCH sampleFrameArray!([index&])[, channels&][, pipeHandle&][, frameCount&]
Parameters
- sampleFrameArray!([index&]) is an array of SINGLE values representing the audio sample frames. Optionally, an index can be specified to determine the starting point in the array.
- channels& is number of channels. This can be 1 (mono) or 2 (stereo). It is assumed as mono if not provided.
- pipeHandle& is a handle to the sound pipe, obtained by using the _SNDOPENRAW function.
- frameCount& is the number of sample frames to play, not the number of array elements. Each frame corresponds to one set of samples per channel.
Description
- Unlike _SNDRAW, _SNDRAWBATCH is designed to play a batch of sample frames. This removes the need to call the underlying audio subsystem for each sample frame and thus improves performance.
- A sample frame is one snapshot of audio data that includes the sound levels for all channels at a specific point in time. In mono audio (1 channel), a sample frame is just 1 value. In stereo audio (2 channels), a sample frame has 2 values: one for the left channel and one for the right channel.
- Stereo audio data should always be interleaved (a left channel sample followed by a right channel sample).
- Ensure that _SNDRAWLEN is comfortably above 0 (until you've finished playing sound). If you get occasional unintended random clicks, this generally means that _SNDRAWLEN has dropped to 0.
- _SNDRAWBATCH 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. However, the 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.
Availability
none
v4.0.0
yes
yes
yes
Examples
- Example 1
- Displays and plays 12 notes from octaves 1 through 9 using _SNDRAWBATCH.
OPTION _EXPLICIT REDIM soundBuffer(0) AS SINGLE DIM AS LONG oct, octave, note DIM fq AS SINGLE, noteStr AS STRING DO COLOR 7 PRINT "Enter the octave 1 to 8 (0 quits!):"; oct = VAL(INPUT$(1)): PRINT oct IF oct = 0 THEN EXIT DO octave = oct - 4 '440 is in the 4th octave, 9th note COLOR oct + 1 PRINT USING "Octave: ##"; oct FOR note = 0 TO 11 'notes C to B fq = FreQ(octave, note, noteStr) PRINT USING "#####.## \\"; fq, noteStr GenWave fq, _SNDRATE, soundBuffer() _SNDRAWBATCH soundBuffer() _SNDRAWDONE DO _LIMIT 60 LOOP WHILE _SNDRAWLEN IF LEN(INKEY$) THEN EXIT DO NEXT LOOP END FUNCTION FreQ (octave AS LONG, note AS LONG, noteStr AS STRING) FreQ = 440! * 2! ^ (octave + (note + 3!) / 12! - 1!) '* 12 note octave starts at C (3 notes up) noteStr = MID$("C C#D D#E F F#G G#A A#B ", note * 2 + 1, 2) END FUNCTION SUB GenWave (frequency AS SINGLE, sampleRate AS LONG, destBuffer() AS SINGLE) REDIM destBuffer(0 TO sampleRate - 1) AS SINGLE DIM sndLoop AS LONG DO WHILE sndLoop < sampleRate destBuffer(sndLoop) = SIN((2! * 4! * ATN(1!) * sndLoop / sampleRate) * frequency) * EXP(-(sndLoop / sampleRate) * 3!) sndLoop = sndLoop + 1 LOOP END SUB |
See also