ProcessFloatSamples.c
/* |
* File: ProcessFloatSamples.c |
* |
* Contains: A filter that implements a lowpass filter with with a 400 Hz cutoff. |
* |
* Version: 1.0 |
* |
* Created: 11-23-2004 |
* |
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#include "ProcessFloatSamples.h" |
/* processSamples - implements a lowpass filter with with a 400 Hz cutoff by using the coefficients in setProcessingParameters() |
in the following difference equation: |
y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] - a1 * y[n-1] - a2 * y[n-2] |
Also saves states for subsequent processing. |
*/ |
void processSamples (float * dataBuffer, UInt32 numSampleFrames, UInt32 numChannels, ParamStructPtr inParamStructPtr, StateStructPtr inStateStructPtr) |
{ |
UInt32 index; |
const UInt32 numSamplesToProcess = numSampleFrames*numChannels; |
float x_n; |
float y_n; |
float b0, b1, b2, a1, a2; |
float xstate1l, xstate2l, ystate1l, ystate2l; |
float xstate1r, xstate2r, ystate1r, ystate2r; |
// set up local copy of parameters |
b0 = inParamStructPtr->b0; |
b1 = inParamStructPtr->b1; |
b2 = inParamStructPtr->b2; |
a1 = inParamStructPtr->a1; |
a2 = inParamStructPtr->a2; |
// set up local copy of state variables |
xstate1l = inStateStructPtr->xstate1l; |
xstate2l = inStateStructPtr->xstate2l; |
ystate1l = inStateStructPtr->ystate1l; |
ystate2l = inStateStructPtr->ystate2l; |
xstate1r = inStateStructPtr->xstate1r; |
xstate2r = inStateStructPtr->xstate2r; |
ystate1r = inStateStructPtr->ystate1r; |
ystate2r = inStateStructPtr->ystate2r; |
// process interleaved floating point data |
for (index = 0; index < numSamplesToProcess; index++) |
{ |
x_n = *dataBuffer; |
// Example device is only stereo or mono; check to maintain correct state variables |
if ( (2 == numChannels) |
&& (1 == (index % 2))) |
{ |
// stereo right channel case |
y_n = b0 * x_n + b1 * xstate1r + b2 * xstate2r - a1 * ystate1r - a2 * ystate2r; |
// update state variables |
xstate2r = xstate1r; |
xstate1r = x_n; |
ystate2r = ystate1r; |
ystate1r = y_n; |
// set output data |
*dataBuffer++ = y_n; |
} |
else |
{ |
// left channel or mono case |
y_n = b0 * x_n + b1 * xstate1l + b2 * xstate2l - a1 * ystate1l - a2 * ystate2l; |
// update state variables |
xstate2l = xstate1l; |
xstate1l = x_n; |
ystate2l = ystate1l; |
ystate1l = y_n; |
// set output data |
*dataBuffer++ = y_n; |
} |
} |
// save states to structure |
inStateStructPtr->xstate1l = xstate1l; |
inStateStructPtr->xstate2l = xstate2l; |
inStateStructPtr->ystate1l = ystate1l; |
inStateStructPtr->ystate2l = ystate2l; |
inStateStructPtr->xstate1r = xstate1r; |
inStateStructPtr->xstate2r = xstate2r; |
inStateStructPtr->ystate1r = ystate1r; |
inStateStructPtr->ystate2r = ystate2r; |
} // processSamples |
void resetProcessingState (StateStructPtr inStateStructPtr) |
{ |
// reset state variables |
inStateStructPtr->xstate1l = 0.0f; |
inStateStructPtr->xstate2l = 0.0f; |
inStateStructPtr->ystate1l = 0.0f; |
inStateStructPtr->ystate2l = 0.0f; |
inStateStructPtr->xstate1r = 0.0f; |
inStateStructPtr->xstate2r = 0.0f; |
inStateStructPtr->ystate1r = 0.0f; |
inStateStructPtr->ystate2r = 0.0f; |
} // resetProcessingState |
void setProcessingParameters (ParamStructPtr inParamStructPtr, UInt32 inSampleRate, UInt32 inNumChannels) |
{ |
// set up our parameters for 400 Hz cutoff lowpass filter |
inParamStructPtr->b0 = 0.000777753436f; |
inParamStructPtr->b1 = 0.001555506871f; |
inParamStructPtr->b2 = 0.000777753436f; |
inParamStructPtr->a1 = -1.913115889852f; |
inParamStructPtr->a2 = 0.916226903594f; |
} // setProcessingParameters |
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