How to use kAudioUnitSubType_LowShelfFilter of kAudioUnitType_Effect which controls bass in core Audio?

Question

i\'m back with one more question related to BASS. I already had posted this question How Can we control bass of music in iPhone, but not get as

Answer 1

Update

Although it's declared in the iOS headers, the Low Shelf AU is not actually available on iOS.

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The parameters of the Low Shelf are different from the iPod EQ.

Parameters are declared and documented in `AudioUnit/AudioUnitParameters.h':

// Parameters for the AULowShelfFilter unit
enum {
  // Global, Hz, 10->200, 80
  kAULowShelfParam_CutoffFrequency = 0,

  // Global, dB, -40->40, 0
  kAULowShelfParam_Gain = 1
};

So after your low shelf AU is created, configure its parameters using AudioUnitSetParameter.

Some initial parameter values you can try would be 120 Hz (kAULowShelfParam_CutoffFrequency) and +6 dB (kAULowShelfParam_Gain) -- assuming your system reproduces bass well, your low frequency content should be twice as loud.

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Can u tell me how can i use this kAULowShelfParam_CutoffFrequency to change the frequency.

If everything is configured right, this should be all that is needed:

assert(lowShelfAU);
const float frequencyInHz = 120.0f;
OSStatus result = AudioUnitSetParameter(lowShelfAU,
                                        kAULowShelfParam_CutoffFrequency,
                                        kAudioUnitScope_Global,
                                        0,
                                        frequencyInHz,
                                        0);
if (noErr != result) {
  assert(0 && "error!");
  return ...;
}