AMR-NB - Revision history

Adam Quantrill: /* GSM OTA format */

2013-03-05T18:06:26Z

GSM OTA format

2013-03-05T18:04:07Z

GSM OTA format

2013-03-05T18:03:03Z

IF2 format

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 | Padding (called "Bit stuffing" in the specification)
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2013-03-05T17:54:40Z

Bit stream frame format

← Older revision		Revision as of 10:54, 5 March 2013
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	== Bit stream frame format ==		== Bit stream frame format ==
	Specification ([http://www.3gpp.org/ftp/Specs/html-info/26101.htm 26.101]) describes two possible frame types - interface formats 1 and 2 (often abbreviated IF1 and IF2). IF2 is byte-aligned. The following tables of data are taken from this specification unless otherwise stated.		Specification ([http://www.3gpp.org/ftp/Specs/html-info/26101.htm 26.101]) describes two possible frame types - interface formats 1 and 2 (often abbreviated IF1 and IF2). IF2 is byte-aligned. The following tables of data are taken from this specification unless otherwise stated. AMR-NB over GSM uses a third slightly different format whose bit-packing is tightly defined by the GSM specs.

	=== IF1 format ===		=== IF1 format ===

2013-03-05T17:52:09Z

Classes

← Older revision		Revision as of 10:52, 5 March 2013
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	* Class A is protected by an 8-bit CRC with polynomial x^8+x^6+x^5+x^4+1 computed over the Class A bits.		* Class A is protected by an 8-bit CRC with polynomial x^8+x^6+x^5+x^4+1 computed over the Class A bits.
			* However for AMR-NB over GSM the CRC is a 6-bit with polynomial x^6+x^5+x^3+x^2+x+1 computed over the Class A bits, and it immediately follows the Class A bits, rather than preceding them. That is, it's between the Class A and Class B bits. [see 3GPP TS 05.03 sec 3.9.4.3]
	* There is no significant step-wise change in subjective importance at class boundaries.		* There is no significant step-wise change in subjective importance at class boundaries.
	* The distribution of bits is ordered from most to least subjective importance at both the class level and within the classes.		* The distribution of bits is ordered from most to least subjective importance at both the class level and within the classes.

2010-02-21T18:23:06Z

← Older revision		Revision as of 11:23, 21 February 2010
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	[[Category:Vocoders]]		[[Category:Vocoders]]
	[[Category:Audio Codecs]]		[[Category:Audio Codecs]]
	~~[[Category: Formats missing in FFmpeg]]~~

2009-08-03T12:55:35Z

← Older revision		Revision as of 05:55, 3 August 2009
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	* Pitch / Adaptive codebook		* Pitch / Adaptive codebook
	* Fixed / Innovative (also algebraic when referring to the codebook)		* Fixed / Innovative (also algebraic when referring to the codebook)
	* Quantified means ~~quantified~~		* Quantified means quantized

2009-08-03T12:55:03Z

← Older revision		Revision as of 05:55, 3 August 2009
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	* Pitch / Adaptive codebook		* Pitch / Adaptive codebook
	* Fixed / Innovative (also algebraic when referring to the codebook)		* Fixed / Innovative (also algebraic when referring to the codebook)
	* Quantified means ~~a value has been chosen for communication. Parameters such as LPC cofficients have a theoretical optimal value, but it is vital that the encoder and decoder agree on the same, "~~quantified~~", value. Hence:~~		* Quantified means quantified
	** the fixed gain is "quantified using [...] scalar quantization" because it is scaled using a transmitted value
	** interpolated LPCs are "quantified and unquantized filter coefficients" because they are determined by the transmitted data (and should not be re-quantized)

2009-08-03T12:33:34Z

← Older revision		Revision as of 05:33, 3 August 2009
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	* Pitch / Adaptive codebook		* Pitch / Adaptive codebook
	* Fixed / Innovative (also algebraic when referring to the codebook)		* Fixed / Innovative (also algebraic when referring to the codebook)
	* Quantified means ~~estimated~~		* Quantified means a value has been chosen for communication. Parameters such as LPC cofficients have a theoretical optimal value, but it is vital that the encoder and decoder agree on the same, "quantified", value. Hence:
			** the fixed gain is "quantified using [...] scalar quantization" because it is scaled using a transmitted value
			** interpolated LPCs are "quantified and unquantized filter coefficients" because they are determined by the transmitted data (and should not be re-quantized)

2009-05-12T19:21:52Z

Update samples URL

← Older revision		Revision as of 12:21, 12 May 2009
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	* samples: http://samples.mplayerhq.hu/amr/		* samples: http://samples.mplayerhq.hu/A-codecs/amr/
	* specification: http://www.3gpp.org/ftp/Specs/html-info/26-series.htm		* specification: http://www.3gpp.org/ftp/Specs/html-info/26-series.htm
	* Wikipedia article: http://en.wikipedia.org/wiki/Adaptive_Multi-Rate		* Wikipedia article: http://en.wikipedia.org/wiki/Adaptive_Multi-Rate