IMA ADPCM - Revision history

Lord Nightmare: add link to original IMA ADPCM specification document

2017-10-30T02:49:15Z

add link to original IMA ADPCM specification document

← Older revision		Revision as of 19:49, 29 October 2017
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	15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767		15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
	};		};

			== IMA ADPCM Specification ==
			A scanned, OCR'ed copy of the original IMA/DVI ADPCM specification document can be found at http://www.cs.columbia.edu/~hgs/audio/dvi/IMA_ADPCM.pdf with original page scans at http://www.cs.columbia.edu/~hgs/audio/dvi/

	[[Category:Audio Codecs]]		[[Category:Audio Codecs]]
	[[Category:ADPCM Audio Codecs]]		[[Category:ADPCM Audio Codecs]]
	[[Category:IMA ADPCM Audio Codecs]]		[[Category:IMA ADPCM Audio Codecs]]

2011-07-15T23:08:34Z

typo correction

← Older revision		Revision as of 16:08, 15 July 2011
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	predictor = predictor + diff		predictor = predictor + diff

	step = ima_step_table[~~step index~~]		step = ima_step_table[step_index]

	Regarding the step index and predictor calculations: Be sure to saturate the computed step index between 0 and 88 (table limits) and the predictor between -32768 and 32767 (signed 16-bit number range). It is possible for these values to outrange which could cause undesirable program behavior if unchecked.		Regarding the step index and predictor calculations: Be sure to saturate the computed step index between 0 and 88 (table limits) and the predictor between -32768 and 32767 (signed 16-bit number range). It is possible for these values to outrange which could cause undesirable program behavior if unchecked.
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	== Decoding Tables ==		== Decoding Tables ==

	int ~~index_table~~[16] = {		int ima_index_table[16] = {
	-1, -1, -1, -1, 2, 4, 6, 8,		-1, -1, -1, -1, 2, 4, 6, 8,
	-1, -1, -1, -1, 2, 4, 6, 8		-1, -1, -1, -1, 2, 4, 6, 8
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	Note that many programs use slight deviations from the following table, but such deviations are negligible:		Note that many programs use slight deviations from the following table, but such deviations are negligible:

	int ~~step_table~~[89] = {		int ima_step_table[89] = {
	7, 8, 9, 10, 11, 12, 13, 14, 16, 17,		7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
	19, 21, 23, 25, 28, 31, 34, 37, 41, 45,		19, 21, 23, 25, 28, 31, 34, 37, 41, 45,

2009-06-24T13:23:42Z

Optimization

← Older revision		Revision as of 06:23, 24 June 2009
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	diff = (2 * nibble + 1) * step / 8		diff = (2 * nibble + 1) * step / 8

			[NOTE: something seems wrong here, e.g. for nibble = 3 and step = 3 we would get with the upper formula
			diff = 0 + 1 + 0 = 1
			and with the lower one
			diff = (2 * 3 + 1) * 3 / 8 = 21 / 8 = 2
			Since with ADPCM errors can propagate forever that seems like a really bad thing...
			]

	== Decoding Tables ==		== Decoding Tables ==

2008-10-24T14:59:43Z

Optimization: fix longstanding math error

2007-04-11T21:48:13Z

Optimization: don't forget to divide by 4

2006-05-30T03:29:50Z

another organization

← Older revision		Revision as of 20:29, 29 May 2006
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	The Interactive Multimedia Association (IMA) developed an ADPCM algorithm designed to be used in entertainment multimedia applications. It is particularly fast to encode and decode and does not strictly require any multiplications or floating point operations.		The [[Interactive Multimedia Association]] (IMA) developed an ADPCM algorithm designed to be used in entertainment multimedia applications. It is particularly fast to encode and decode and does not strictly require any multiplications or floating point operations.

	While the encoding and decoding algorithms remain more or less constant across different IMA implementations, the specific on-disk data formats vary. This page describes the common IMA decoding algorithm. See the [[:Category:IMA ADPCM Audio Codecs]] page for various formats used for storing the data on disk.		While the encoding and decoding algorithms remain more or less constant across different IMA implementations, the specific on-disk data formats vary. This page describes the common IMA decoding algorithm. See the [[:Category:IMA ADPCM Audio Codecs]] page for various formats used for storing the data on disk.

2006-05-30T01:35:19Z

Reverted edits by Beverlysegovia (Talk); changed back to last version by Multimedia Mike

← Older revision		Revision as of 18:35, 29 May 2006
Line 24:		Line 24:
	step = ima_step_table[step index]		step = ima_step_table[step index]

	Regarding the step index and predictor calculations: Be sure to saturate the computed step index between 0 and 88 (table limits) and the predictor between -32768 and 32767 (signed 16-bit number range). It is possible for these values to outrange which could		Regarding the step index and predictor calculations: Be sure to saturate the computed step index between 0 and 88 (table limits) and the predictor between -32768 and 32767 (signed 16-bit number range). It is possible for these values to outrange which could cause undesirable program behavior if unchecked.



	cause undesirable program behavior if unchecked.

	== Optimization ==		== Optimization ==

2006-05-30T00:48:42Z

Decoding IMA

← Older revision		Revision as of 17:48, 29 May 2006
Line 24:		Line 24:
	step = ima_step_table[step index]		step = ima_step_table[step index]

	Regarding the step index and predictor calculations: Be sure to saturate the computed step index between 0 and 88 (table limits) and the predictor between -32768 and 32767 (signed 16-bit number range). It is possible for these values to outrange which could cause undesirable program behavior if unchecked.		Regarding the step index and predictor calculations: Be sure to saturate the computed step index between 0 and 88 (table limits) and the predictor between -32768 and 32767 (signed 16-bit number range). It is possible for these values to outrange which could



			cause undesirable program behavior if unchecked.

	== Optimization ==		== Optimization ==

2006-03-24T18:09:30Z

revert spam/vandalism

2006-03-24T08:37:31Z