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Commit 6f31f461 authored by Antti S. Lankila's avatar Antti S. Lankila
Browse files

Use 1st order high shelf instead of RC filter. 

This admittedly sounds almost the same, but the advantage of
shelving is with more high-frequency content being mixed. That being
said, the used shelving is reasonably steep (16 dB).
parent 51835b8c

libs/audioflinger/AudioDSP.cpp

+19 −2
Original line number Diff line number Diff line
@@ -196,6 +196,19 @@ void Biquad::setHighShelf(float center_frequency, float sampling_frequency, floa 
    setCoefficients(a0, a1, a2, b0, b1, b2);

}



void Biquad::setHighShelf1(float center_frequency, float sampling_frequency, float db_gain)

{

    float w0 = 2 * (float) M_PI * center_frequency / sampling_frequency;

    float A = powf(10, db_gain/40);



    float b0 = sinf(w0 / 2) + cosf(w0 / 2) * A;

    float b1 = sinf(w0 / 2) - cosf(w0 / 2) * A;

    float a0 = sinf(w0 / 2) + cosf(w0 / 2) / A;

    float a1 = sinf(w0 / 2) - cosf(w0 / 2) / A;



    setCoefficients(a0, a1, 0, b0, b1, 0);

}



void Biquad::setBandPass(float center_frequency, float sampling_frequency, float resonance)

{

    float w0 = 2 * (float) M_PI * center_frequency / sampling_frequency;
@@ -411,8 +424,12 @@ void EffectHeadphone::configure(const float samplingFrequency) { 


    mReverbDelayL.setParameters(mSamplingFrequency, 0.030f);

    mReverbDelayR.setParameters(mSamplingFrequency, 0.030f);

    mLowpassL.setRC(700.0f, mSamplingFrequency);

    mLowpassR.setRC(700.0f, mSamplingFrequency);

    /* the -3 dB point is around 700 Hz, similar to the classic design

     * in bs2b. */

    mLowpassL.setHighShelf1(1500.0f, mSamplingFrequency, -16.0f);

    mLowpassR.setHighShelf1(1500.0f, mSamplingFrequency, -16.0f);

    /* Rockbox has a 0.3 ms delay line (13 samples at 44100 Hz), but

     * I think it makes the whole effect sound pretty bad so I skipped it! */

}



void EffectHeadphone::setDeep(bool deep)

libs/audioflinger/AudioDSP.h

+1 −0
Original line number Diff line number Diff line
@@ -68,6 +68,7 @@ class Biquad { 
    void setBandPass(float cf, float sf, float resonance);

    void setLowShelf(float cf, float sf, float gain, float slope);

    void setHighShelf(float cf, float sf, float gain, float slope);

    void setHighShelf1(float cf, float sf, float gain);

    void reset();

    int32_t process(int16_t x0);

};