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Commit 00c25009 authored by Antti S. Lankila's avatar Antti S. Lankila
Browse files

Add audio dithering for intermediate quantizations 

Mask quantization effects under classic high-pass triangular
dithering.

Change-Id: I567ad3a7ae31002f04569ae0dec3685de2846d24
parent 76a4c6df

media/libeffects/cyanogen-dsp/Effect.cpp

+2 −2
Original line number Diff line number Diff line
@@ -65,7 +65,7 @@ int32_t Effect::command(uint32_t cmdCode, uint32_t cmdSize, void *pCmdData, uint 
    switch (cmdCode) {

    case EFFECT_CMD_ENABLE:

    case EFFECT_CMD_DISABLE: {

	enable = cmdCode == EFFECT_CMD_ENABLE;

	mEnable = cmdCode == EFFECT_CMD_ENABLE;

	int32_t *replyData = (int32_t *) pReplyData;

	*replyData = 0;

	break;
@@ -110,7 +110,7 @@ int32_t Effect::command(uint32_t cmdCode, uint32_t cmdSize, void *pCmdData, uint 


int32_t Effect::process(audio_buffer_t *in, audio_buffer_t *out)

{

    if (! enable) {

    if (! mEnable) {

        for (uint32_t i = 0; i < in->frameCount; i ++) {

	    int32_t tmpL = read(in, i * 2);

	    int32_t tmpR = read(in, i * 2 + 1);

media/libeffects/cyanogen-dsp/Effect.h

+19 −5
Original line number Diff line number Diff line
@@ -3,6 +3,12 @@ 
#include <stdint.h>

#include <media/EffectApi.h>



static inline uint16_t prng() {

    static uint32_t seed;

    seed = seed * 1664525 + 1013904223;

    return seed >> 14;

}



class Effect {

    private:

    audio_format_e mFormatIn;
@@ -10,9 +16,18 @@ class Effect { 
    effect_buffer_access_e mAccessMode;



    protected:

    bool enable;

    bool mEnable;

    float mSamplingRate;

    uint32_t mChannels;

    uint16_t mPreviousRandom;



    /* High-passed triangular probability density function. */

    inline int32_t triangularDither16() {

        uint16_t newRandom = prng();

        int32_t rnd = mPreviousRandom - newRandom;

        mPreviousRandom = newRandom;

        return rnd;

    }



    inline int32_t read(audio_buffer_t *in, int32_t idx) {

	switch (mFormatIn) {
@@ -51,10 +66,9 @@ class Effect { 
	    }

	}



	/* I should probably apply dithering for S15 / U8. */

	switch (mFormatOut) {

	case SAMPLE_FORMAT_PCM_S15:

	    sample >>= 8;

	    sample = (sample + (triangularDither16() >> 8)) >> 8;

	    if (sample > 32767) {

		sample = 32767;

	    }
@@ -65,7 +79,7 @@ class Effect { 
	    break;



	case SAMPLE_FORMAT_PCM_U8:

	    sample >>= 16;

	    sample = (sample + triangularDither16()) >> 16;

	    sample += 128;

	    if (sample > 255) {

		sample = 255;