Opus tuning - Revision history

MrZeus: /* Parameters */

2016-11-14T14:44:21Z

Parameters

← Older revision		Revision as of 14:44, 14 November 2016
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	== Trim (7 7 8) ==		== Trim (7 7 8) ==

	Trim controls the bit allocation balance between low and high frequencies. This is currently computed by '''alloc_trim_analysis()''' around '''[https://github.com/xiph/opus/blob/master/celt/celt_encoder.c#L780 line 780 of celt_encoder.c]'''.		Trim controls the bit allocation balance between low and high frequencies.

			This is currently computed by '''alloc_trim_analysis()''' around '''[https://github.com/xiph/opus/blob/master/celt/celt_encoder.c#L780 line 780 of celt_encoder.c]'''.

	A high trim value signals more bits to the low frequencies, while a lower trim value signals more bits to the high frequencies.		A high trim value signals more bits to the low frequencies, while a lower trim value signals more bits to the high frequencies.
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	== Stereo Saving (4 6 6) ==		== Stereo Saving (4 6 6) ==

	Stereo saving controls the bitrate reduction applied for stereo signals with a narrow image. It is computed in alloc_trim_analysis(), around line ~~733~~ of celt_encoder.c. It is applied in celt_encode_with_ec(), around line ~~1558 or~~ celt_encoder.c.		Stereo saving controls the bitrate reduction applied for stereo signals with a narrow image.

			It is computed in '''alloc_trim_analysis()''', around '''[https://github.com/xiph/opus/blob/master/celt/celt_encoder.c#L780 line 780 of celt_encoder.c]'''.
			It is applied in '''celt_encode_with_ec()''', around '''[https://github.com/xiph/opus/blob/master/celt/celt_encoder.c#L1329 line 1329 of celt_encoder.c]'''.

	== Spreading (4 7 7) ==		== Spreading (4 7 7) ==

	spreading_decision() bands.c around line 413.		'''spreading_decision()''' in '''bands.c''' around line 413.

	== Tapset (1 4 9) ==		== Tapset (1 4 9) ==

	spreading_decision() bands.c around line 413.		'''spreading_decision()''' in '''bands.c''' around line 413.

	== Transient Estimator (10 8 8) ==		== Transient Estimator (10 8 8) ==

	transient_analysis() celt_encoder.c around line 209.		'''transient_analysis()''' in '''celt_encoder.c''' around line 209.

	=== Transient Boost (8 6 6) ===		=== Transient Boost (8 6 6) ===

	transient_analysis() celt_encoder.c around line 209.		'''transient_analysis()''' in '''celt_encoder.c''' around line 209.

	== TF Estimator (6 6 9) ==		== TF Estimator (6 6 9) ==

	tf_analysis() in celt_encoder.c around line 475.		'''tf_analysis()''' in '''celt_encoder.c''' around line 475.

	== Intensity Threshold (7 8 3) ==		== Intensity Threshold (7 8 3) ==

	The intensity threshold is the first band to be coded as intensity stereo. When a band is intensity-coded, the coding noise in that band is lower, at the expense of a narrower stereo image.		The intensity threshold is the first band to be coded as intensity stereo. When a band is intensity-coded, the coding noise in that band is lower, at the expense of a narrower stereo image.
	In celt_encoder.c around line 1492:
			In '''[https://github.com/xiph/opus/blob/master/celt/celt_encoder.c#L1932 celt_encoder.c, around line 1492]''':

	static const opus_val16 intensity_thresholds[21]=		static const opus_val16 intensity_thresholds[21]=
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	{ 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 4, 5, 6, 8, 12};		{ 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 4, 5, 6, 8, 12};

	The intensity_thresholds[] table defines the intensity threshold as a function of the ''effective bitrate''. For example, between 63 and 68 kb/s effective rate, the intensity threshold is 16. Above 130 kb/s, intensity stereo is completely disabled. Note that for 20 ms frames, the effective rate is equal to the actual rate, minus 4 kb/s.		The '''intensity_thresholds[]''' table defines the intensity threshold as a function of the ''effective bitrate''.
			For example, between 63 and 68 kb/s effective rate, the intensity threshold is 16.
			Above 130 kb/s, intensity stereo is completely disabled.

			Note that for 20 ms frames, the effective rate is equal to the ''actual rate minus 4 kb/s''.

	== Skip Threshold (3 6 4) ==		== Skip Threshold (3 6 4) ==
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	The important constants are the 7 and the 9. They determine the minimum allocation for a band to be coded, with hysteresis. The units are 1/16 bit per sample.		The important constants are the 7 and the 9. They determine the minimum allocation for a band to be coded, with hysteresis. The units are 1/16 bit per sample.

	The code above means that if a band was coded in the previous frame, it needs 7/16 bit per sample in this frame, but if it wasn't coded, then it needs 9/16 bits. If a band isn't coded, then ~~it's~~ contents ~~gets~~ replaced by a copy of the lower MDCT spectrum, or by noise~~. Decreasing these values increases the quality of the highest frequency bands, at the expense of all other bands~~.		Decreasing these values increases the quality of the highest frequency bands, at the expense of all other bands.

			The code above means that if a band was coded in the previous frame, it needs 7/16 bit per sample in this frame, but if it wasn't coded, then it needs 9/16 bits. If a band isn't coded, then its contents get replaced by a copy of the lower MDCT spectrum, or by noise.

	== Mode/Bandwidth Decisions (6 4 4) ==		== Mode/Bandwidth Decisions (6 4 4) ==

	[[Category:Opus]]		[[Category:Opus]]

MrZeus: /* Tonality (10 5 1) */

2016-11-14T12:56:51Z

Tonality (10 5 1)

← Older revision		Revision as of 12:56, 14 November 2016
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	tonal_target = target + (opus_int32)((coded_bins << BITRES) * 1.2f * tonal);		tonal_target = target + (opus_int32)((coded_bins << BITRES) * 1.2f * tonal);

	Replacing the constant 1.2f will change the impact of tonality on the bit-rate. The higher the value, the higher the bit-rate of tonal frames/samples.		Replacing the constant '''1.2f''' will change the impact of tonality on the bit-rate. The higher the value, the higher the bit-rate of tonal frames/samples.

	== Trim (7 7 8) ==		== Trim (7 7 8) ==

MrZeus: /* DynAlloc (5 5 9) */

2016-11-14T12:56:22Z

DynAlloc (5 5 9)

← Older revision		Revision as of 12:56, 14 November 2016
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	== DynAlloc (5 5 9) ==		== DynAlloc (5 5 9) ==

	''Dynamic allocation'' is the part of the Opus bitstream that makes it possible to increase the allocation of any band(s). This is currently computed in dynalloc_analysis() around line ~~810~~ of celt_encoder.c.		''Dynamic allocation'' is the part of the Opus bitstream that makes it possible to increase the allocation of any band(s).

			This is currently computed in '''dynalloc_analysis()''' around '''[https://github.com/xiph/opus/blob/master/celt/celt_encoder.c#L956 line 956 of celt_encoder.c]'''.

	== Stereo Saving (4 6 6) ==		== Stereo Saving (4 6 6) ==

MrZeus: /* Trim (7 7 8) */

2016-11-14T12:54:45Z

Trim (7 7 8)

← Older revision		Revision as of 12:54, 14 November 2016
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	== Trim (7 7 8) ==		== Trim (7 7 8) ==

	Trim controls the bit allocation balance between low and high frequencies. This is currently computed by alloc_trim_analysis() around line ~~677~~ of celt_encoder.c. A high trim value signals more bits to the low frequencies, while a lower trim value signals more bits to the high frequencies.		Trim controls the bit allocation balance between low and high frequencies. This is currently computed by '''alloc_trim_analysis()''' around '''[https://github.com/xiph/opus/blob/master/celt/celt_encoder.c#L780 line 780 of celt_encoder.c]'''.

			A high trim value signals more bits to the low frequencies, while a lower trim value signals more bits to the high frequencies.

	== DynAlloc (5 5 9) ==		== DynAlloc (5 5 9) ==

MrZeus: /* Tonality (10 5 1) */

2016-11-14T12:52:20Z

Tonality (10 5 1)

← Older revision		Revision as of 12:52, 14 November 2016
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	== Tonality (10 5 1) ==		== Tonality (10 5 1) ==

	~~around~~ line ~~1574~~ of celt_encoder.c:		Around '''[https://github.com/xiph/opus/blob/master/celt/celt_encoder.c#L1276 line 1276 of celt_encoder.c]''':

	tonal_target = target + (opus_int32)((coded_bins<<BITRES)1.2ftonal);		tonal_target = target + (opus_int32)((coded_bins << BITRES) * 1.2f * tonal);

	Replacing the constant 1.2f will change the impact of tonality on the bit-rate. The higher value, the higher the bit-rate of tonal frames/samples.		Replacing the constant 1.2f will change the impact of tonality on the bit-rate. The higher the value, the higher the bit-rate of tonal frames/samples.

	== Trim (7 7 8) ==		== Trim (7 7 8) ==

MrZeus: capitalise categories, add whitespace

2016-11-14T12:42:05Z

capitalise categories, add whitespace

← Older revision		Revision as of 12:42, 14 November 2016
Line 1:		Line 1:
	This page is meant to provide help on tuning the current Opus encoder. It assumes you are working on the master branch, not 1.0.x. As work progresses, some info (especially any line numbers) may become outdated. The numbers in parentheses represent (in order):		This page is meant to provide help on tuning the current Opus encoder. It assumes you are working on the '''master''' branch, not 1.0.x.

			As work progresses, some info (especially any line numbers) may become outdated.

			The numbers in parentheses represent (in order):
	* Impact on quality		* Impact on quality
	* Quality of current tuning		* Quality of current tuning
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	= Parameters =		= Parameters =

	These are some parameters that can be tuned to improve the Opus encoder quality (in no particular order)		These are some parameters that can be tuned to improve the Opus encoder quality (in no particular order).
	== ~~tonality~~ (10 5 1) ==
			== Tonality (10 5 1) ==

	around line 1574 of celt_encoder.c:		around line 1574 of celt_encoder.c:
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	Replacing the constant 1.2f will change the impact of tonality on the bit-rate. The higher value, the higher the bit-rate of tonal frames/samples.		Replacing the constant 1.2f will change the impact of tonality on the bit-rate. The higher value, the higher the bit-rate of tonal frames/samples.

	== ~~trim~~ (7 7 8) ==		== Trim (7 7 8) ==

	Trim controls the bit allocation balance between low and high frequencies. This is currently computed by alloc_trim_analysis() around line 677 of celt_encoder.c. A high trim value signals more bits to the low frequencies, while a lower trim value signals more bits to the high frequencies.		Trim controls the bit allocation balance between low and high frequencies. This is currently computed by alloc_trim_analysis() around line 677 of celt_encoder.c. A high trim value signals more bits to the low frequencies, while a lower trim value signals more bits to the high frequencies.

	== ~~dynalloc~~ (5 5 9) ==		== DynAlloc (5 5 9) ==

	''Dynamic allocation'' is the part of the Opus bitstream that makes it possible to increase the allocation of any band(s). This is currently computed in dynalloc_analysis() around line 810 of celt_encoder.c.		''Dynamic allocation'' is the part of the Opus bitstream that makes it possible to increase the allocation of any band(s). This is currently computed in dynalloc_analysis() around line 810 of celt_encoder.c.

	== ~~stereo saving~~ (4 6 6) ==		== Stereo Saving (4 6 6) ==

	Stereo saving controls the bitrate reduction applied for stereo signals with a narrow image. It is computed in alloc_trim_analysis(), around line 733 of celt_encoder.c. It is applied in celt_encode_with_ec(), around line 1558 or celt_encoder.c.		Stereo saving controls the bitrate reduction applied for stereo signals with a narrow image. It is computed in alloc_trim_analysis(), around line 733 of celt_encoder.c. It is applied in celt_encode_with_ec(), around line 1558 or celt_encoder.c.

	== ~~spreading~~ (4 7 7) ==		== Spreading (4 7 7) ==

	spreading_decision() bands.c around line 413.		spreading_decision() bands.c around line 413.

	== ~~tapset~~ (1 4 9) ==		== Tapset (1 4 9) ==

	spreading_decision() bands.c around line 413.		spreading_decision() bands.c around line 413.

	== ~~transient estimator~~ (10 8 8) ==		== Transient Estimator (10 8 8) ==

	transient_analysis() celt_encoder.c around line 209.		transient_analysis() celt_encoder.c around line 209.

	===~~transient boost~~ (8 6 6) ===		=== Transient Boost (8 6 6) ===

	transient_analysis() celt_encoder.c around line 209.		transient_analysis() celt_encoder.c around line 209.

	== ~~tf estimator~~ (6 6 9) ==		== TF Estimator (6 6 9) ==

	tf_analysis() in celt_encoder.c around line 475.		tf_analysis() in celt_encoder.c around line 475.

	== Intensity ~~threshold~~ (7 8 3) ==		== Intensity Threshold (7 8 3) ==

	The intensity threshold is the first band to be coded as intensity stereo. When a band is intensity-coded, the coding noise in that band is lower, at the expense of a narrower stereo image.		The intensity threshold is the first band to be coded as intensity stereo. When a band is intensity-coded, the coding noise in that band is lower, at the expense of a narrower stereo image.
Line 60:		Line 65:
	The intensity_thresholds[] table defines the intensity threshold as a function of the ''effective bitrate''. For example, between 63 and 68 kb/s effective rate, the intensity threshold is 16. Above 130 kb/s, intensity stereo is completely disabled. Note that for 20 ms frames, the effective rate is equal to the actual rate, minus 4 kb/s.		The intensity_thresholds[] table defines the intensity threshold as a function of the ''effective bitrate''. For example, between 63 and 68 kb/s effective rate, the intensity threshold is 16. Above 130 kb/s, intensity stereo is completely disabled. Note that for 20 ms frames, the effective rate is equal to the actual rate, minus 4 kb/s.

	== ~~skip threshold~~ (3 6 4) ==		== Skip Threshold (3 6 4) ==

	In function interp_bits2pulses() in rate.c around line 356.		In function interp_bits2pulses() in rate.c around line 356.
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	if (codedBands<=start+2 \|\| (band_bits > ((j<prev?7:9)*band_width<<LM<<BITRES)>>4 && j<=signalBandwidth))		if (codedBands<=start+2 \|\| (band_bits > ((j<prev?7:9)*band_width<<LM<<BITRES)>>4 && j<=signalBandwidth))

	The important constants are the 7 and the 9. They determine the minimum allocation for a band to be coded, with hysteresis. The units are 1/16 bit per sample. The code above means that if a band was coded in the previous frame, it needs 7/16 bit per sample in this frame, but if it wasn't coded, then it needs 9/16 bits. If a band isn't coded, then it's contents gets replaced by a copy of the lower MDCT spectrum, or by noise. Decreasing these values increases the quality of the highest frequency bands, at the expense of all other bands.		The important constants are the 7 and the 9. They determine the minimum allocation for a band to be coded, with hysteresis. The units are 1/16 bit per sample.

			The code above means that if a band was coded in the previous frame, it needs 7/16 bit per sample in this frame, but if it wasn't coded, then it needs 9/16 bits. If a band isn't coded, then it's contents gets replaced by a copy of the lower MDCT spectrum, or by noise. Decreasing these values increases the quality of the highest frequency bands, at the expense of all other bands.

	== ~~mode~~/~~bandwidth decisions~~ (6 4 4) ==		== Mode/Bandwidth Decisions (6 4 4) ==

	[[Category:Opus]]		[[Category:Opus]]

MrZeus at 15:32, 18 August 2015

2015-08-18T15:32:08Z

← Older revision		Revision as of 15:32, 18 August 2015
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	== mode/bandwidth decisions (6 4 4) ==		== mode/bandwidth decisions (6 4 4) ==

			[[Category:Opus]]

Jmspeex at 05:52, 5 February 2013

2013-02-05T05:52:36Z

← Older revision		Revision as of 05:52, 5 February 2013
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	{ 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 4, 5, 6, 8, 12};		{ 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 4, 5, 6, 8, 12};

	The intensity_thresholds[] table defines the intensity threshold as a function of the ''effective bitrate''. For example, between 63 and 68 kb/s, the intensity threshold is 16. Above 130 kb/s, intensity stereo is completely disabled.		The intensity_thresholds[] table defines the intensity threshold as a function of the ''effective bitrate''. For example, between 63 and 68 kb/s effective rate, the intensity threshold is 16. Above 130 kb/s, intensity stereo is completely disabled. Note that for 20 ms frames, the effective rate is equal to the actual rate, minus 4 kb/s.

	== skip threshold (3 6 4) ==		== skip threshold (3 6 4) ==

Jmspeex at 20:39, 7 January 2013

2013-01-07T20:39:02Z

← Older revision		Revision as of 20:39, 7 January 2013
Line 62:		Line 62:
	== skip threshold (3 6 4) ==		== skip threshold (3 6 4) ==

	interp_bits2pulses() in rate.c around line 356.		In function interp_bits2pulses() in rate.c around line 356.

	if (codedBands<=start+2 \|\| (band_bits > ((j<prev?7:9)*band_width<<LM<<BITRES)>>4 && j<=signalBandwidth))		if (codedBands<=start+2 \|\| (band_bits > ((j<prev?7:9)*band_width<<LM<<BITRES)>>4 && j<=signalBandwidth))

	The important constants are the 7 and the 9. They determine the minimum allocation for a band to be coded, with hysteresis. The units are 1/16 bit per sample.		The important constants are the 7 and the 9. They determine the minimum allocation for a band to be coded, with hysteresis. The units are 1/16 bit per sample. The code above means that if a band was coded in the previous frame, it needs 7/16 bit per sample in this frame, but if it wasn't coded, then it needs 9/16 bits. If a band isn't coded, then it's contents gets replaced by a copy of the lower MDCT spectrum, or by noise. Decreasing these values increases the quality of the highest frequency bands, at the expense of all other bands.

	== mode/bandwidth decisions (6 4 4) ==		== mode/bandwidth decisions (6 4 4) ==

Jmspeex at 20:32, 7 January 2013

2013-01-07T20:32:48Z

← Older revision		Revision as of 20:32, 7 January 2013
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	interp_bits2pulses() in rate.c around line 356.		interp_bits2pulses() in rate.c around line 356.

			if (codedBands<=start+2 \|\| (band_bits > ((j<prev?7:9)*band_width<<LM<<BITRES)>>4 && j<=signalBandwidth))

			The important constants are the 7 and the 9. They determine the minimum allocation for a band to be coded, with hysteresis. The units are 1/16 bit per sample.
	== mode/bandwidth decisions (6 4 4) ==		== mode/bandwidth decisions (6 4 4) ==