G726 Class Reference
[Audio Codec - ITU-T Recomendation G726]

A class which implements ITU-T (formerly CCITT) Recomendation G726 "40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM)". More...

#include <G726.h>

List of all members.

Public Types
enum	Law { uLaw = 0, ALaw = 1, PCM16 = 2 }
enum	Rate { Rate16kBits = 2, Rate24kBits = 3, Rate32kBits = 4, Rate40kBits = 5 }
Public Member Functions
	G726 ()
void	Reset ()
void	SetLaw (Law law)
void	SetRate (Rate rate)
unsigned	Encode (unsigned pcm)
unsigned	Decode (unsigned adpcm)
unsigned	Encode (void dst, int dstOffset, const void src, size_t srcSize)
unsigned	Decode (void dst, const void src, int srcOffset, unsigned srcSize)
Private Member Functions
void	InputPCMFormatConversionAndDifferenceSignalComputation (unsigned S, int SE, int &D)
	FIGURE 4/G.726 from Section 4.2.1 - Input PCM format conversion and difference signal computation.
void	AdaptiveQuantizer (int D, unsigned Y, unsigned &I)
	FIGURE 5/G.726 from Section 4.2.2 - Adaptive quantizer.
void	InverseAdaptiveQuantizer (unsigned I, unsigned Y, unsigned &DQ)
	FIGURE 6/G.726 from Section 4.2.3 - Inverse adaptive quantizer.
void	QuantizerScaleFactorAdaptation1 (unsigned AL, unsigned &Y)
	FIGURE 7/G.726 (Part 1) from Section 4.2.4 - Quantizer scale factor adaptation.
void	QuantizerScaleFactorAdaptation2 (unsigned I, unsigned Y)
	FIGURE 7/G.726 (Part 2) from Section 4.2.4 - Quantizer scale factor adaptation.
void	AdaptationSpeedControl1 (unsigned &AL)
	FIGURE 8/G.726 (Part 1) from Section 4.2.5 - Adaptation speed control.
void	AdaptationSpeedControl2 (unsigned I, unsigned y, unsigned TDP, unsigned TR)
	FIGURE 8/G.726 (Part 2) from Section 4.2.5 - Adaptation speed control.
void	AdaptativePredictorAndReconstructedSignalCalculator1 (int &SE, int &SEZ)
	FIGURE 9/G.726 (Part1) from Section 4.2.6 - Adaptative predictor and reconstructed signal calculator.
void	AdaptativePredictorAndReconstructedSignalCalculator2 (unsigned DQ, unsigned TR, int SE, int SEZ, int &SR, int &A2P)
	FIGURE 9/G.726 (Part2) from Section 4.2.6 - Adaptative predictor and reconstructed signal calculator.
void	ToneAndTransitionDetector1 (unsigned DQ, unsigned &TR)
	FIGURE 10/G.726 (Part 1) from Section 4.2.7 - Tone and transition detector.
void	ToneAndTransitionDetector2 (int A2P, unsigned TR, unsigned &TDP)
	FIGURE 10/G.726 (Part 2) from Section 4.2.7 - Tone and transition detector.
void	OutputPCMFormatConversionAndSynchronousCodingAdjustment (int SR, int SE, unsigned Y, unsigned I, unsigned &SD)
	FIGURE 11/G.726 from Section 4.2.8 - Output PCM format conversion and synchronous coding adjustment.
void	DifferenceSignalComputation (int SL, int SE, int &D)
	FIGURE A.4/G.726 from Section A.3.3 - Difference signal computation.
void	OutputLimiting (int SR, int &S0)
	FIGURE A.5/G.726 from Section A.3.5 - Output limiting (decoder only).
unsigned	EncodeDecode (unsigned input, bool encode)
	The top level method which implements the complete algorithm for both encoding and decoding.

Detailed Description

A class which implements ITU-T (formerly CCITT) Recomendation G726 "40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM)".

G726 replaces recomendations G721 and G723.

Note, this implemetation reproduces bugs found in the G191 reference implementation of G726. These bugs can be controlled by the IMPLEMENT_G191_BUGS macro.

See also:: IMPLEMENT_G191_BUGS

Version:

2005-02-13

Added constructor G726(),
Added Encode(void* dst, int dstOffset, const void* src, size_t srcSize) and
Added Decode(void* dst, const void* src, int srcOffset, unsigned srcSize);

2006-05-20

Changed code to use standard typedefs, e.g. replaced uint8 with uint8_t, and made use of size_t.

2007-01-13

Fixed GCC compilation warnings.

Definition at line 62 of file G726.h.

Member Enumeration Documentation

enum G726::Law

Enumeration used to specify the coding law used for encoder input and decoder output.

Enumerator:

uLaw	u law
ALaw	A law
PCM16	16 bit uniform PCM values. These are 'left justified' values corresponding to the 14 bit values in G726 Annex A.

Definition at line 68 of file G726.h.

enum G726::Rate

Enumeration used to specify the ADPCM bit-rate.

Enumerator:

Rate16kBits	16k bits per second (2 bits per ADPCM sample)
Rate24kBits	24k bits per second (3 bits per ADPCM sample)
Rate32kBits	32k bits per second (4 bits per ADPCM sample)
Rate40kBits	40k bits per second (5 bits per ADPCM sample)

Definition at line 78 of file G726.h.

Constructor & Destructor Documentation

G726::G726 ( )

Contructor which initialises the object to the reset state.

See also:: Reset()

Since:: 2005-02-13

Definition at line 90 of file G726.h.

Member Function Documentation

void G726::Reset ( )

Clears the internal state variables to their 'reset' values. Call this function before starting to decode/encode a new audio stream.

Definition at line 1192 of file G726.cpp.

void G726::SetLaw ( Law law )

Set the encoding law used for encoder input and decoder output.

Parameters:

law

The encoding law.

Definition at line 1215 of file G726.cpp.

void G726::SetRate ( Rate rate )

Set the ADPCM bit-rate used for encoder output and decoder intput.

Parameters:

rate

The ADPCM bit-rate.

Definition at line 1222 of file G726.cpp.

unsigned G726::Encode ( unsigned pcm )

Encodes a single PCM value as an ADPCM value.

Precondition:: The coding law and ADPCM bit-rate should have been previous initialised with SetLaw() and SetRate().

Parameters:

pcm

The PCM value to encode. The bits in this value which lie outside the range of values for the currently set encoding law, are ignored.

Returns:: The encoded ADPCM value. The number of significant bits in this value are dependant on the bit-rate set by SetRate(). Unused bits are set to zero.

Definition at line 1229 of file G726.cpp.

unsigned G726::Decode ( unsigned adpcm )

Decodes a single ADPCM value into a PCM value.

Precondition:: The coding law and ADPCM bit-rate should have been previous initialised with SetLaw() and SetRate().

Parameters:

adpcm

The ADPCM value to decode. The bits in this value which lie outside the range of values for the currently set bit-rate, are ignored.

Returns:: The decoded PCM value. This is in the format specified by SetLaw().

See also:: IMPLEMENT_G191_BUGS

Definition at line 1235 of file G726.cpp.

unsigned G726::Encode	(	void *	dst,
		int	dstOffset,
		const void *	src,
		size_t	srcSize
	)

Encode a buffer of uniform PCM values into ADPCM values.

Each ADPCM value only occupies the minimum number of bits required and successive values occupy adjacent bit positions. E.g. Four 3 bit ADPCM values (A,B,C,D) are stored in two successive bytes like this: 1st byte: ccbbbaaa 2nd byte: ----dddc. Note that any unused bits in the last byte are set to zero.

Precondition:: The coding law and ADPCM bit-rate should have been previous initialised with SetLaw() and SetRate().

Parameters:

	dst	Pointer to location to store ADPCM values.
	dstOffset	Offset from dst, in number-of-bits, at which the decoded values will be stored. I.e. the least significant bit of the first ADPCM value will be stored in byte dst[dstOffset>>3] at bit position dstOffset&7 Where the bit 0 is the least significant bit in a byte and bit 7 is the most significant bit.
	src	Pointer to the buffer of PCM values to be converted.
	srcSize	The size in bytes of the buffer at src. Must be a multiple of the size of a single PCM sample.

Returns:: The number of bits were stored in the dst buffer.

Since:: 2005-02-13

Definition at line 1242 of file G726.cpp.

unsigned G726::Decode	(	void *	dst,
		const void *	src,
		int	srcOffset,
		unsigned	srcSize
	)

Decode a buffer of ADPCM values into uniform PCM values.

Each ADPCM value only occupies the minimum number of bits required and successive values occupy adjacent bit positions. E.g. Four 3 bit ADPCM values (A,B,C,D) are stored in two successive bytes like this: 1st byte: ccbbbaaa 2nd byte: ----dddc.

Precondition:: The coding law and ADPCM bit-rate should have been previous initialised with SetLaw() and SetRate().

Parameters:

	dst	Pointer to location to store PCM values.
	src	Pointer to the buffer of ADPCM values to be converted.
	srcOffset	Offset from src, in number-of-bits, from which the ADPCM values will be read. I.e. the least significant bit of the first ADPCM value will be read from byte src[srcOffset>>3] at bit position srcOffset&7 Where the bit 0 is the least significant bit in a byte and bit 7 is the most significant bit.
	srcSize	The number of bits to be read from the buffer at src. Must be a multiple of the size of a single ADPCM value.

Returns:: The number of bytes which were stored in the dst buffer.

See also:: IMPLEMENT_G191_BUGS

Since:: 2005-02-13

Definition at line 1315 of file G726.cpp.

unsigned G726::EncodeDecode	(	unsigned	input,
		bool	encode
	)			`[private]`

The top level method which implements the complete algorithm for both encoding and decoding.

Parameters:

	input	Either the PCM input to the encoder or the ADPCM input to the decoder.
	encode	A flag which if true makes this method perform the encode function. If the flag is false then the decode function is performed.

Returns:: Either the ADPCM output to the encoder or the PCM output to the decoder.

Definition at line 1130 of file G726.cpp.

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

audio/G726.h
audio/G726.cpp

G726 Class Reference [Audio Codec - ITU-T Recomendation G726]

Public Types

Public Member Functions

Private Member Functions

Detailed Description

Member Enumeration Documentation

Constructor & Destructor Documentation

Member Function Documentation

G726 Class Reference
[Audio Codec - ITU-T Recomendation G726]