AudioCompressor Class Reference

#include <audiocompressor.h>

Public Member Functions
	AudioCompressor ()
	~AudioCompressor ()
void	fillLUT ()
	4 bands More...
void	fillLUT2 ()
	8 bands (default) More...
void	fillALaw ()
	A-law compression to 8 bits. More...
void	fillULaw ()
	u-law compression to 8 bits More...
int16_t	compress (int16_t sample)
int8_t	compress8 (int16_t sample)

Private Member Functions
int8_t	ALaw_Encode (int16_t number)
int8_t	MuLaw_Encode (int16_t number)

Private Attributes
int16_t	m_lut [32768]

Static Private Attributes
static const uint16_t	ALAW_MAX = 0xFFF
static const uint16_t	MULAW_MAX = 0x1FFF
static const uint16_t	MULAW_BIAS = 33

Detailed Description

Definition at line 25 of file audiocompressor.h.

Constructor & Destructor Documentation

AudioCompressor()

AudioCompressor::AudioCompressor

(

)

Definition at line 26 of file audiocompressor.cpp.

References fillLUT2().

{
    fillLUT2();
}

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~AudioCompressor()

AudioCompressor::~AudioCompressor

(

)

Definition at line 31 of file audiocompressor.cpp.

{}

Member Function Documentation

ALaw_Encode()

int8_t AudioCompressor::ALaw_Encode ( int16_t  number )

private

Definition at line 139 of file audiocompressor.cpp.

References ALAW_MAX.

Referenced by fillALaw().

{
    uint16_t mask = 0x800;
    uint8_t sign = 0;
    uint8_t position = 11;
    uint8_t lsb = 0;

    if (number < 0)
    {
       number = -number;
       sign = 0x80;
    }

    if (number > ALAW_MAX) {
       number = ALAW_MAX;
    }

    for (; ((number & mask) != mask && position >= 5); mask >>= 1, position--) {
    }

    lsb = (number >> ((position == 4) ? (1) : (position - 4))) & 0x0f;

    return (sign | ((position - 4) << 4) | lsb) ^ 0x55;
}

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compress()

int16_t AudioCompressor::compress

(

int16_t

sample

)

Definition at line 102 of file audiocompressor.cpp.

References abs(), and m_lut.

Referenced by AMBEWorker::upsample().

{
    int16_t sign = sample < 0 ? -1 : 1;
    int16_t abs = sample < 0 ? -sample : sample;
    return sign * m_lut[abs];
}

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compress8()

int8_t AudioCompressor::compress8

(

int16_t

sample

)

Definition at line 109 of file audiocompressor.cpp.

References m_lut.

Referenced by AudioNetSink::write().

{
    return m_lut[sample/2 + 16384];
}

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fillALaw()

void AudioCompressor::fillALaw

(

)

A-law compression to 8 bits.

Definition at line 88 of file audiocompressor.cpp.

References ALaw_Encode(), i, and m_lut.

Referenced by AudioNetSink::setParameters().

{
    for (int i=-16384; i<16384; i++) {
        m_lut[i+16384] = ALaw_Encode(2*i);
    }
}

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fillLUT()

void AudioCompressor::fillLUT

(

)

4 bands

Definition at line 34 of file audiocompressor.cpp.

References i, and m_lut.

{
    for (int i=0; i<8192; i++) {
        m_lut[i] = (24576/8192)*i;
    }

    for (int i=8192; i<2*8192; i++) {
        m_lut[i] = 24576 + 0.5f*(i-8192);
    }

    for (int i=2*8192; i<3*8192; i++) {
        m_lut[i] = 24576 + 4096 + 0.25f*(i-2*8192);
    }

    for (int i=3*8192; i<4*8192; i++) {
        m_lut[i] = 24576 + 4096 + 2048 + 0.125f*(i-3*8192);
    }
}

fillLUT2()

void AudioCompressor::fillLUT2

(

)

8 bands (default)

Definition at line 53 of file audiocompressor.cpp.

References i, and m_lut.

Referenced by AudioCompressor().

{
    for (int i=0; i<4096; i++) {
        m_lut[i] = (24576/4096)*i;
    }

    for (int i=4096; i<2*4096; i++) {
        m_lut[i] = 24576 + 0.5f*(i-4096);
    }

    for (int i=2*4096; i<3*4096; i++) {
        m_lut[i] = 24576 + 2048 + 0.25f*(i-2*4096);
    }

    for (int i=3*4096; i<4*4096; i++) {
        m_lut[i] = 24576 + 2048 + 1024 + 0.125f*(i-3*4096);
    }

    for (int i=4*4096; i<5*4096; i++) {
        m_lut[i] = 24576 + 2048 + 1024 + 512 + 0.0625f*(i-4*4096);
    }

    for (int i=5*4096; i<6*4096; i++) {
        m_lut[i] = 24576 + 2048 + 1024 + 512 + 256 + 0.03125f*(i-5*4096);
    }

    for (int i=6*4096; i<7*4096; i++) {
        m_lut[i] = 24576 + 2048 + 1024 + 512 + 256 + 128 + 0.015625f*(i-6*4096);
    }

    for (int i=7*4096; i<8*4096; i++) {
        m_lut[i] = 24576 + 2048 + 1024 + 512 + 256 + 128 + 64 + 0.0078125f*(i-7*4096);
    }
}

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fillULaw()

void AudioCompressor::fillULaw

(

)

u-law compression to 8 bits

Definition at line 95 of file audiocompressor.cpp.

References i, m_lut, and MuLaw_Encode().

Referenced by AudioNetSink::setParameters().

{
    for (int i=-16384; i<16384; i++) {
        m_lut[i+16384] = MuLaw_Encode(2*i);
    }
}

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MuLaw_Encode()

int8_t AudioCompressor::MuLaw_Encode ( int16_t  number )

private

Definition at line 175 of file audiocompressor.cpp.

References MULAW_BIAS, and MULAW_MAX.

Referenced by fillULaw().

{
   uint16_t mask = 0x1000;
   uint8_t sign = 0;
   uint8_t position = 12;
   uint8_t lsb = 0;

   if (number < 0)
   {
      number = -number;
      sign = 0x80;
   }

   number += MULAW_BIAS;

   if (number > MULAW_MAX) {
      number = MULAW_MAX;
   }

   for (; ((number & mask) != mask && position >= 5); mask >>= 1, position--) {
   }

   lsb = (number >> (position - 4)) & 0x0f;

   return (~(sign | ((position - 5) << 4) | lsb));
}

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Member Data Documentation

ALAW_MAX

const uint16_t AudioCompressor::ALAW_MAX = 0xFFF

staticprivate

Definition at line 42 of file audiocompressor.h.

Referenced by ALaw_Encode().

m_lut

int16_t AudioCompressor::m_lut[32768]

private

Definition at line 41 of file audiocompressor.h.

Referenced by compress(), compress8(), fillALaw(), fillLUT(), fillLUT2(), and fillULaw().

MULAW_BIAS

const uint16_t AudioCompressor::MULAW_BIAS = 33

staticprivate

Definition at line 44 of file audiocompressor.h.

Referenced by MuLaw_Encode().

MULAW_MAX

const uint16_t AudioCompressor::MULAW_MAX = 0x1FFF

staticprivate

Definition at line 43 of file audiocompressor.h.

Referenced by MuLaw_Encode().

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The documentation for this class was generated from the following files:

• sdrbase/audio/audiocompressor.h
• sdrbase/audio/audiocompressor.cpp