Apple Newton Utilities Guia do Utilizador descarregar pdf (Página 563)

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101

CHAPTER 14

Sound

Using Sound 14-9

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

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