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Commit a2284ac5 authored by Antti S. Lankila's avatar Antti S. Lankila
Browse files

Make Headphone DSP with just 1 biquad 

Subtracting the left and right channels could be argued to
separate the center channel from the left/right channel and the
DSP therefore gets applied to panned sounds only. This halves the
cost of the filtering and eliminates the bass boost issue that bs2b
compensates for with a highboost filter.

I also adjusted the delay-to-level spatial filter to try to get slightly
more consistent perception of panning across the frequency spectrum.
parent 57e7bb29

libs/audioflinger/AudioDSP.cpp

+6 −19
Original line number Diff line number Diff line
@@ -334,10 +334,6 @@ EffectTone::EffectTone() 
}



EffectTone::~EffectTone() {

    for (int32_t i = 0; i < 4; i ++) {

        delete &mFilterL[i];

        delete &mFilterR[i];

    }

}



void EffectTone::configure(const float samplingFrequency) {
@@ -402,10 +398,6 @@ EffectHeadphone::EffectHeadphone() 


EffectHeadphone::~EffectHeadphone()

{

    delete &mReverbDelayL;

    delete &mReverbDelayR;

    delete &mLowpassL;

    delete &mLowpassR;

}



void EffectHeadphone::configure(const float samplingFrequency) {
@@ -414,8 +406,7 @@ void EffectHeadphone::configure(const float samplingFrequency) { 
    mReverbDelayL.setParameters(mSamplingFrequency, 0.030f);

    mReverbDelayR.setParameters(mSamplingFrequency, 0.030f);

    /* the -3 dB point is around 650 Hz, giving about 300 us to work with */

    mLowpassL.setHighShelf(800.0f, mSamplingFrequency, -12.0f, 0.72f);

    mLowpassR.setHighShelf(800.0f, mSamplingFrequency, -12.0f, 0.72f);

    mLowpass.setHighShelf(850.0f, mSamplingFrequency, -10.0f, 0.72f);

    /* 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! */

}
@@ -469,14 +460,13 @@ void EffectHeadphone::process(int32_t* inout, int32_t frames) 
        dataL += dryL;

        dataR += dryR;



        /* Lowpass filter to estimate head shadow. */

        dataL = mLowpassL.process(dataL >> fixedPointDecimals);

        dataR = mLowpassR.process(dataR >> fixedPointDecimals);

        /* Lowpass filter difference to estimate head shadow. */

        int32_t diff = mLowpass.process((dataL - dataR) >> fixedPointDecimals);

        /* 28 bits */

        

        /* Mix right-to-left and vice versa. */

        inout[0] += dataR >> 1;

        inout[1] += dataL >> 1;

        /* Mix difference between channels. */

        inout[0] = dataL - (diff >> 1);

        inout[1] = dataR + (diff >> 1);

        inout += 2;

    }

}
@@ -507,9 +497,6 @@ AudioDSP::AudioDSP() 


AudioDSP::~AudioDSP()

{

    delete &mCompression;

    delete &mTone;

    delete &mHeadphone;

}



void AudioDSP::configure(const float samplingRate)

libs/audioflinger/AudioDSP.h

+1 −1
Original line number Diff line number Diff line
@@ -120,7 +120,7 @@ class EffectHeadphone : public Effect { 


    Delay mReverbDelayL, mReverbDelayR;

    int32_t mDelayDataL, mDelayDataR;

    Biquad mLowpassL, mLowpassR;

    Biquad mLowpass;



    public:

    EffectHeadphone();