Sound

Using Sound

Pitch Shifting

14

In general, you can set the value of a sound frame's

samplingRate

slot to any

float value less than that specified by the

kFloat22kRate

constant. However, this

usually results in poor sound quality. What generally works best is to take an 11
kHz sound and play it at some higher rate. Of course, 22 kHz sound resources
cannot be played at any higher sampling rate.

You can experiment with pitch shifting by playing sounds in the Inspector using
the

PlaySoundSync

function. You can use any of the ROM sounds or your own

custom sounds. The following example shows how to shift a sound's pitch by
altering the value of the sound frame's

samplingRate

slot. Remember when

setting this slot that

samplingRate

must be a value of type

float

.

// keep a copy of original for future use
origSound := clone(ROM_simpleBeep);

// make a copy to modify
mySound := Clone(origSound);

// play the original sound
PlaySoundSync(mySound);

// play at half original pitch
mySound.samplingRate := origSound.samplingRate/2;
PlaySoundSync(mySound);

// note how easily we can return to normal pitch
mySound.samplingRate := origSound.samplingRate;

// play at twice speed
mySound.samplingRate := origSound.samplingRate*2;
PlaySoundSync(mySound);

By using the output from a control view to alter the value of the sound frame's

samplingRate

slot, you can allow the user to interactively modify the pitch of

playback. The following example code changes the value of the

samplingRate

slot according to the setting of a

protoSlider

view:

theSlider.changedSlider := func()begin
if viewValue = maxValue then

mySound.samplingRate := originalRate
else mySound.samplingRate := (viewValue*1.01);

PlaySoundSync(mySound);
end