Audio Effects

130 Audio Effects: Theory, Implementation and Application

channelData[i] = in * (1.0f - depth_ *

lfo(ph, waveform_));

// Update the carrier and LFO phases, keeping them in

// the range 0-1

ph += frequency_*inverseSampleRate;

if(ph >= 1.0)

ph -= 1.0;

}

The code uses the variable ph to keep track of the current phase of the

LFO. The tremolo effect itself is simply a change in volume modulated by

the value of the LFO. This tremolo example includes a choice of LFO styles,

as implemented in the lfo() function.

float lfo(float phase, int waveform)

{

switch(waveform)

{

case kWaveformTriangle:

if(phase < 0.25f)

return 0.5f + 2.0f*phase;

else if(phase < 0.75f)

return 1.0f - 2.0f*(phase - 0.25f);

else

return 2.0f*(phase-0.75f);

case kWaveformSquare: