LAME Y switch - Revision history

Beardgoggles: Minor page reformatting.

2019-12-03T17:24:39Z

Minor page reformatting.

← Older revision		Revision as of 17:24, 3 December 2019
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	This article describes the function of '''the -Y switch''' in the [[LAME]] encoder ~~commandline~~.		This article describes the function of '''the -Y switch''' in the [[LAME]] command-line encoder, and tries to clarify what the switch does and what it does not do. It is frequently misinterpreted, like [[joint stereo]], and mistaken for a filter.<ref>{{ha\|url=https://hydrogenaud.io/index.php?topic=79841.msg697111#msg697111\|title=-V2 gives way too high bitrate!?!}}</ref>

			In explaining what it does, in easy terms and in technical terms, the reader should get a better understanding of the motivation behind and the usage of the switch.

	==The short definition==		==The short definition==
	* The -Y switch tells [[LAME]] not to encode the highest frequencies '''accurately''', '''if doing so''' causes disproportional increases in bitrate.		* The -Y switch tells LAME not to encode the highest frequencies '''accurately''', '''if doing so''' causes disproportional increases in [[bitrate]].


	Other ways to say it include:		Other ways to say it include:
	* The -Y switch tells [[LAME]] to use a more '''coarse representation''' for the highest frequencies, in the parts where it would cause an over-encoding of all the other bands.		* The -Y switch tells LAME to use a more '''coarse representation''' for the highest frequencies, in the parts where it would cause an over-encoding of all the other bands.
	* The -Y switch tells [[LAME]] to '''not be so strict''' with the higher frequencies, '''if''' they are going to cause an increase of bitrate.		* The -Y switch tells LAME to '''not be so strict''' with the higher frequencies, '''if''' they are going to cause an increase of bitrate.


	; The -Y switch is not a lowpass filter.		; The -Y switch is not a lowpass filter.
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	==The technical definition==		==The technical definition==

	===How is audio stored in MP3===		===How is audio stored in MP3===
	* MP3 audio is stored in the frequency domain (values for frequencies) instead of the time domain (values for samples)		* MP3 audio is stored in the frequency domain (values for frequencies) instead of the time domain (values for samples)
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	* If the encoder determines that sfb21 needs more resolution, it has no way to decrease the scale factor of sfb21 alone, since there is no such scale factor.		* If the encoder determines that sfb21 needs more resolution, it has no way to decrease the scale factor of sfb21 alone, since there is no such scale factor.
	* The only way to increase the resolution on sfb21 is therefore to reduce the global gain quantization, since global gain applies to all bands.		* The only way to increase the resolution on sfb21 is therefore to reduce the global gain quantization, since global gain applies to all bands.
	* Scale factors are stored as a relative value of global gain (just the difference is stored). Let's call this value the relative factor.		* Scale factors are stored as a relative value of global gain (just the difference is stored). Let's call this value the "relative factor".
	* To balance the reduction of global gain, the scale factor of the other bands should increase. Consequently, the relative factor decreases.		* To balance the reduction of global gain, the scale factor of the other bands should increase. Consequently, the relative factor decreases.
	* The relative factor can be decreased until it reaches zero. At that point, any further reduction of global gain implies that the band will use more resolution than needed.		* The relative factor can be decreased until it reaches zero. At that point, any further reduction of global gain implies that the band will use more resolution than needed.
	* The encoder is forced to increase the bitrate needed, not only because of the frequencies at or above 16Khz, but also because other bands below the sfb21 have excessive resolution.		* The encoder is forced to increase the bitrate needed, not only because of the frequencies at or above 16Khz, but also because other bands below the sfb21 have excessive resolution.

	===~~The~~ -Y switch ~~and the sfb21~~ ===		'''Source:''' [http://www.mp3-tech.org/content/?Mp3%20Limitations MP3' Tech - Mp3 Limitations] {{webarchive\|https://web.archive.org/web/20120222124415/http://www.mp3-tech.org/content/?Mp3%20Limitations\|2012-02-22}}
	[[LAME]] implements the -Y switch as a way to activate the alternate logic that CBR uses in respect to quantization noise in the sfb21 band.
			===sfb21 and the -Y switch===
			LAME implements the -Y switch as a way to activate the alternate logic that [[CBR]] uses in respect to quantization noise in the sfb21 band.
	* The encoder determines the desired quantization noise within the sfbs. The scale factors are choosen acording to these values.		* The encoder determines the desired quantization noise within the sfbs. The scale factors are choosen acording to these values.
	* If -Y switch is not used (either implicitly or explicitly), sfb21 gets evaluated and the global gain is set accordingly.		* If -Y switch is not used (either implicitly or explicitly), sfb21 gets evaluated and the global gain is set accordingly.
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	The ones that would normally have needed higher resolution to satisfy the criteria of the psy-model don't receive that treatment, while ones that wouldn't need higher resolution are unaffected by the Y switch. '''The Y switch prevents global gain quantization from being decreased solely to accomodate the needs of sfb21'''.		The ones that would normally have needed higher resolution to satisfy the criteria of the psy-model don't receive that treatment, while ones that wouldn't need higher resolution are unaffected by the Y switch. '''The Y switch prevents global gain quantization from being decreased solely to accomodate the needs of sfb21'''.

	==~~The~~ -Y switch ~~and CBR/ABR~~ ==		==CBR/ABR and the -Y switch==
	The -Y switch can only be activated in [[LAME#Technical information\|VBR mode]]. By default, -~~V 3 to~~ -~~V 9~~ use -Y. -~~V 0, -V 1, and~~ -~~V 2~~ do not. Consequently, adding -Y is only useful for the highest three VBR settings.		The -Y switch can only be activated in [[LAME#Technical information\|VBR mode]]. By default, {{code\|-V3}}–{{code\|-V9}} use -Y. {{code\|-V0}}–{{code\|-V2}} do not. Consequently, adding -Y is only useful for the highest three VBR settings.

	This is because in CBR and ABR modes, the encoder uses -Y implicitly.		This is because in CBR and [[ABR]] modes, the encoder uses -Y implicitly. Specifically, LAME targets a given bitrate, and adjusts the quantization steps until that target is reached.
	Specifically, LAME targets a given bitrate, and adjusts the quantization steps until that target is reached.

	Since the sfb21 does not have quantization, its quantization noise is not evaluated.		Since the sfb21 does not have quantization, its quantization noise is not evaluated.
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	This is the same treatment as using -Y in VBR mode.		This is the same treatment as using -Y in VBR mode.

	~~==Motivation behind this article==~~		==Notes==
	~~The article tries to clarify what the switch does and what it does not do. It is frequently misinterpreted, like [[Joint_stereo\|joint stereo]], and mistaken for a filter.~~

	~~In explaining what it does, in easy terms and in technical terms, the reader should get a better understanding of the motivation behind and the usage of the switch.~~

	~~==See also==~~
	* [[MP3\|Description of the MPEG layer 3 format]]
	* [http://www.hydrogenaudio.org/forums/index.php?showtopic=79841&st=0 Hydrogenaudio thread discussing this article]

	==Notes ~~and references~~==

	For long blocks, the last scalefactor band is sfb21. For short blocks it is sfb12. The frequency at which it starts also depends on the sampling rate. The value of ~16Khz is for 44.1Khz material.		For long blocks, the last scalefactor band is sfb21. For short blocks it is sfb12. The frequency at which it starts also depends on the sampling rate. The value of ~16Khz is for 44.1Khz material.

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	This article has been brought up partially with comments fom Aleron Ives, robert and benski.		This article has been brought up partially with comments fom Aleron Ives, robert and benski.
	~~The definition~~ of the ~~sfb21 problem is reworded from the article at [http:~~/~~/www.mp3-tech.org/content/?Mp3%20Limitations Mp3 tech.org]~~
			==See also==
			* [[MP3\|Description of the MPEG Audio Layer III format]]

			==References==
			<references/>

37.188.71.160: /* The -Y switch and the sfb21 */

2016-01-31T01:11:12Z

The -Y switch and the sfb21

← Older revision		Revision as of 01:11, 31 January 2016
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	[[LAME]] implements the -Y switch as a way to activate the alternate logic that CBR uses in respect to quantization noise in the sfb21 band.		[[LAME]] implements the -Y switch as a way to activate the alternate logic that CBR uses in respect to quantization noise in the sfb21 band.
	* The encoder determines the desired quantization noise within the sfbs. The scale factors are choosen acording to these values.		* The encoder determines the desired quantization noise within the sfbs. The scale factors are choosen acording to these values.
	* If -Y switch is not used (either implicitly or explicitly), sfb21 gets evaluated and the global gain is set ~~acordingly~~.		* If -Y switch is not used (either implicitly or explicitly), sfb21 gets evaluated and the global gain is set accordingly.
	* Adding -Y lets the encoder ignore whatever quantization noise will be in sfb21.		* Adding -Y lets the encoder ignore whatever quantization noise will be in sfb21.

Mjb: Mjb moved page LAME Y Switch to LAME Y switch: Avoid Excessive Capitalization Of Headings And Page Titles

2014-09-10T19:30:45Z

Mjb moved page LAME Y Switch to LAME Y switch: Avoid Excessive Capitalization Of Headings And Page Titles

← Older revision	Revision as of 19:30, 10 September 2014
(No difference)

Danhash: remove whitespace, add bullets

2012-08-18T21:39:35Z

remove whitespace, add bullets

← Older revision		Revision as of 21:39, 18 August 2012
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	; The -Y switch is not a lowpass filter.		; The -Y switch is not a lowpass filter.
	: It allows high frequencies (>=16Khz) to exist, it just alters its accuracy. If their values are very small it can quantize them to zero (but probably the psychoacoustic analyzer will decide to simply remove them instead).		: It allows high frequencies (>=16Khz) to exist, it just alters its accuracy. If their values are very small it can quantize them to zero (but probably the psychoacoustic analyzer will decide to simply remove them instead).


	==The technical definition==		==The technical definition==
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	The ones that would normally have needed higher resolution to satisfy the criteria of the psy-model don't receive that treatment, while ones that wouldn't need higher resolution are unaffected by the Y switch. '''The Y switch prevents global gain quantization from being decreased solely to accomodate the needs of sfb21'''.		The ones that would normally have needed higher resolution to satisfy the criteria of the psy-model don't receive that treatment, while ones that wouldn't need higher resolution are unaffected by the Y switch. '''The Y switch prevents global gain quantization from being decreased solely to accomodate the needs of sfb21'''.


	==The -Y switch and CBR/ABR ==		==The -Y switch and CBR/ABR ==
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	This is the same treatment as using -Y in VBR mode.		This is the same treatment as using -Y in VBR mode.



	==Motivation behind this article==		==Motivation behind this article==
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	In explaining what it does, in easy terms and in technical terms, the reader should get a better understanding of the motivation behind and the usage of the switch.		In explaining what it does, in easy terms and in technical terms, the reader should get a better understanding of the motivation behind and the usage of the switch.


	==See also==		==See also==
			* [[MP3\|Description of the MPEG layer 3 format]]
	[[MP3\|Description of the MPEG layer 3 format]]		* [http://www.hydrogenaudio.org/forums/index.php?showtopic=79841&st=0 Hydrogenaudio thread discussing this article]

	[http://www.hydrogenaudio.org/forums/index.php?showtopic=79841&st=0 Hydrogenaudio thread discussing this article]


	==Notes and references==		==Notes and references==

Danhash: moved LAME Y SWITCH to LAME Y Switch: capitalization

2012-08-18T21:38:42Z

moved LAME Y SWITCH to LAME Y Switch: capitalization

← Older revision	Revision as of 21:38, 18 August 2012
(No difference)

JAZ: adding credits to mp3-tech.org

2010-04-01T12:42:18Z

adding credits to mp3-tech.org

← Older revision		Revision as of 12:42, 1 April 2010
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	This article has been brought up partially with comments fom Aleron Ives, robert and benski.		This article has been brought up partially with comments fom Aleron Ives, robert and benski.
			The definition of the sfb21 problem is reworded from the article at [http://www.mp3-tech.org/content/?Mp3%20Limitations Mp3 tech.org]

JAZ: Corrected the definition of the sfb21 problem and improved the explanation of how scale factors are stored.

2010-04-01T12:35:56Z

Corrected the definition of the sfb21 problem and improved the explanation of how scale factors are stored.

← Older revision		Revision as of 12:35, 1 April 2010
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	* If the encoder determines that sfb21 needs more resolution, it has no way to decrease the scale factor of sfb21 alone, since there is no such scale factor.		* If the encoder determines that sfb21 needs more resolution, it has no way to decrease the scale factor of sfb21 alone, since there is no such scale factor.
	* The only way to increase the resolution on sfb21 is therefore to reduce the global gain quantization, since global gain applies to all bands.		* The only way to increase the resolution on sfb21 is therefore to reduce the global gain quantization, since global gain applies to all bands.
	* ~~The encoder can reduce the~~ global gain ~~as long as it~~ is ~~above zero~~.		* Scale factors are stored as a relative value of global gain (just the difference is stored). Let's call this value the relative factor.
	* If global gain ~~is zero~~, ~~resolution will need to be increased (and quantization lowered) '''on every~~ other ~~scale~~ factor ~~band'''~~.		* To balance the reduction of global gain, the scale factor of the other bands should increase. Consequently, the relative factor decreases.
	* The ~~result is~~ that ~~unnecessary resolution is applied to every other band~~, so the ~~bits used in all the other bands~~ will ~~increase, causing the bitrate to rise~~.		* The relative factor can be decreased until it reaches zero. At that point, any further reduction of global gain implies that the band will use more resolution than needed.
	* The encoder is forced to ~~excessively~~ increase the bitrate of the ~~file just so that~~ the ~~frequencies >= 16 kHz will be adequately quantized~~.		* The encoder is forced to increase the bitrate needed, not only because of the frequencies at or above 16Khz, but also because other bands below the sfb21 have excessive resolution.

	===The -Y switch and the sfb21 ===		===The -Y switch and the sfb21 ===
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	==Notes and references==		==Notes and references==

	~~In MPEG1 (32, 44, 48Khz)~~, the last scalefactor band is sfb21. ~~In MPEG2 (16,22,24Khz),~~ it is sfb12. The frequency at which it starts also depends on the sampling rate. The value of ~16Khz is for 44.1Khz material.		For long blocks, the last scalefactor band is sfb21. For short blocks it is sfb12. The frequency at which it starts also depends on the sampling rate. The value of ~16Khz is for 44.1Khz material.

	Global gain and scale factors are not independent. The latter is expressed as a difference of the former.		Global gain and scale factors are not independent when stored to the file. The latter is expressed as a difference of the former. (relative factor)

	* The global gain is the global quantization step size, with a value range between 0 and 255.		* The global gain is the global quantization step size, with a value range between 0 and 255.
	* The ~~scale~~ factor per band is the amount to reduce the global quantization step size. The range of this value is dependant on the band.		* The relative factor per band is the amount to reduce the global quantization step size. The range of this value is dependant on the band.
	Consequently, there are just a reduced amount of values to use.		Consequently, there are just a reduced amount of values to use and a change to global gain needs to be compensated by a change in the relative factor.

	This article has been brought up partially with comments fom Aleron Ives, robert and benski.		This article has been brought up partially with comments fom Aleron Ives, robert and benski.

JAZ: Orthographic revision, extension on some points.

2010-04-01T10:04:01Z

Orthographic revision, extension on some points.

← Older revision		Revision as of 10:04, 1 April 2010
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	Other ways to say it include:		Other ways to say it include:
	* The -Y switch tells [[LAME]] to use a more '''coarse representation''' for the highest frequencies, in the parts where it would cause an over-encoding of all the other bands.		* The -Y switch tells [[LAME]] to use a more '''coarse representation''' for the highest frequencies, in the parts where it would cause an over-encoding of all the other bands.
	* The -Y switch tells [[LAME]] to '''not be so strict''' with the higher frequencies, '''IF''' they are going to cause an increase of bitrate.		* The -Y switch tells [[LAME]] to '''not be so strict''' with the higher frequencies, '''if''' they are going to cause an increase of bitrate.


	; The -Y switch is not a lowpass filter.		; The -Y switch is not a lowpass filter.
	: It allows high frequencies (>=16Khz) to exist, it just alters its accuracy. If their values are very small it can quantize them to zero (but probably the psychoacoustic analyzer will decide to remove them ~~anyway~~).		: It allows high frequencies (>=16Khz) to exist, it just alters its accuracy. If their values are very small it can quantize them to zero (but probably the psychoacoustic analyzer will decide to simply remove them instead).


Line 17:		Line 17:

	===How is audio stored in MP3===		===How is audio stored in MP3===
	* MP3 audio is stored in the frequency domain (values for frequencies) instead of time domain (values for samples)		* MP3 audio is stored in the frequency domain (values for frequencies) instead of the time domain (values for samples)
	* Frequencies are analyzed and stored in groups, known as bands.		* Frequencies are analyzed and stored in groups, known as bands.
	* Bands are quantized to make them compress better.		* Bands are quantized to make them compress better.
	* ''Scale factor'' refers to how much quantization (loss of precision) is applied to each band, where higher quantization causes greater compression, ~~but also~~ less variation between the minimum and maximum values (resolution).		* ''Scale factor'' refers to how much quantization (loss of precision) is applied to each band, where higher quantization causes greater compression, and consequently less variation between the minimum and maximum values (resolution).
	* Each band has its own scale factor, so that its quantization can be adjusted independently from the others.		* Each band has its own scale factor, so that its quantization can be adjusted independently from the others.
			*The exception is scalefactor band 21 (sfb21), which does not have a scale factor. This band stores frequencies of 16 kHz and above.
	* Global gain is an extra quantizer that affects all bands simultaneously.		* Global gain is an extra quantizer that affects all bands simultaneously.
			(See section notes about scalefactors and global gain)

	===What is the scalefactor band 21 (sfb21) defect===		===What is the scalefactor band 21 (sfb21) defect===
	* The last band is called '''sfb21''', and '''does not have''' a scale factor. This band stores frequencies at 16 kHz and above.		* If the encoder determines that sfb21 needs more resolution, it has no way to decrease the scale factor of sfb21 alone, since there is no such scale factor.
	* If the encoder determines that sfb21 needs more resolution, it has no way to decrease the ~~scalefactor~~ of sfb21 alone, since there is no such scale factor.		* The only way to increase the resolution on sfb21 is therefore to reduce the global gain quantization, since global gain applies to all bands.
	* The only way to increase the resolution on sfb21 is therefore to reduce the global gain quantization.
	* The encoder can reduce the global gain as long as it is above zero.		* The encoder can reduce the global gain as long as it is above zero.
	* If global gain is zero, resolution will need to be increased (and quantization be lowered) '''on every other scale factor band'''.		* If global gain is zero, resolution will need to be increased (and quantization lowered) '''on every other scale factor band'''.
	* The result is that unnecessary resolution is applied to every other band, so the bits used in all the other bands will increase ~~and ultimately~~, the bitrate ~~too~~.		* The result is that unnecessary resolution is applied to every other band, so the bits used in all the other bands will increase, causing the bitrate to rise.
	* The encoder is forced to increase ~~in excess~~ the bitrate of the file just so that the frequencies >= 16 kHz will be adequately quantized.		* The encoder is forced to excessively increase the bitrate of the file just so that the frequencies >= 16 kHz will be adequately quantized.

	===The -Y switch and the sfb21 ===		===The -Y switch and the sfb21 ===
	[[LAME]] implements the -Y switch as a way to activate the alternate logic that CBR uses in respect of quantization noise in the sfb21 band.		[[LAME]] implements the -Y switch as a way to activate the alternate logic that CBR uses in respect to quantization noise in the sfb21 band.
	* The encoder determines the desired quantization noise within the sfbs. The ~~scalefactors~~ are choosen acording to these values.		* The encoder determines the desired quantization noise within the sfbs. The scale factors are choosen acording to these values.
	* If -Y switch is not used (either ~~implicitely~~ or ~~explicitely~~), sfb21 gets evaluated and the global gain is set acordingly.		* If -Y switch is not used (either implicitly or explicitly), sfb21 gets evaluated and the global gain is set acordingly.
	* Adding -Y lets the encoder ignore whatever quantization noise will be in sfb21.		* Adding -Y lets the encoder ignore whatever quantization noise will be in sfb21.

	The result is that all the 16 kHz + frequencies still get encoded~~, but the~~ ones that would normally have needed higher resolution to satisfy the criteria of the psy-model don't receive that treatment, while ones that wouldn't need higher resolution are unaffected by the Y switch.		The result is that all the 16 kHz and above frequencies still get encoded.

			The ones that would normally have needed higher resolution to satisfy the criteria of the psy-model don't receive that treatment, while ones that wouldn't need higher resolution are unaffected by the Y switch. '''The Y switch prevents global gain quantization from being decreased solely to accomodate the needs of sfb21'''.


	==The -Y switch and CBR/ABR ==		==The -Y switch and CBR/ABR ==
	The -Y switch ~~is used along with the~~ [[LAME#Technical information\|VBR ~~modes~~]].		The -Y switch can only be activated in [[LAME#Technical information\|VBR mode]]. By default, -V 3 to -V 9 use -Y. -V 0, -V 1, and -V 2 do not. Consequently, adding -Y is only useful for the highest three VBR settings.

			This is because in CBR and ABR modes, the encoder uses -Y implicitly.
			Specifically, LAME targets a given bitrate, and adjusts the quantization steps until that target is reached.

	~~For CBR and ABR, the encoder uses -Y implicitely.~~
	~~Concretely, the encoder targets a given bitrate, and adjusts the quantization steps until that target is reached.~~
	Since the sfb21 does not have quantization, its quantization noise is not evaluated.		Since the sfb21 does not have quantization, its quantization noise is not evaluated.

			This is the same treatment as using -Y in VBR mode.



	==Motivation ~~under~~ this article==		==Motivation behind this article==
	The article tries to clarify what the switch does and what it does not. It is frequently misinterpreted, like [[Joint_stereo\|joint stereo]], and ~~identified with~~ a filter.		The article tries to clarify what the switch does and what it does not do. It is frequently misinterpreted, like [[Joint_stereo\|joint stereo]], and mistaken for a filter.
	In explaining what it does, in easy terms and in technical terms, the reader should get a better understanding of the motivation and the usage of ~~such~~ switch.
			In explaining what it does, in easy terms and in technical terms, the reader should get a better understanding of the motivation behind and the usage of the switch.


Line 61:		Line 68:

	[http://www.hydrogenaudio.org/forums/index.php?showtopic=79841&st=0 Hydrogenaudio thread discussing this article]		[http://www.hydrogenaudio.org/forums/index.php?showtopic=79841&st=0 Hydrogenaudio thread discussing this article]


	==Notes and references==		==Notes and references==

	In MPEG1 (32, 44, 48Khz), the last scalefactor band is sfb21. In MPEG2 (16,22,24Khz), it is sfb12. The frequency at which it starts also depends on the sampling rate. The value of ~16Khz is for 44.1Khz material.		In MPEG1 (32, 44, 48Khz), the last scalefactor band is sfb21. In MPEG2 (16,22,24Khz), it is sfb12. The frequency at which it starts also depends on the sampling rate. The value of ~16Khz is for 44.1Khz material.

			Global gain and scale factors are not independent. The latter is expressed as a difference of the former.

			* The global gain is the global quantization step size, with a value range between 0 and 255.
			* The scale factor per band is the amount to reduce the global quantization step size. The range of this value is dependant on the band.
			Consequently, there are just a reduced amount of values to use.

	This article has been brought up partially with comments fom Aleron Ives, robert and benski.		This article has been brought up partially with comments fom Aleron Ives, robert and benski.

JAZ: LAME Y SWITH moved to LAME Y SWITCH: typo.

2010-03-31T19:43:05Z

LAME Y SWITH moved to LAME Y SWITCH: typo.

← Older revision	Revision as of 19:43, 31 March 2010
(No difference)

JAZ at 13:01, 31 March 2010

2010-03-31T13:01:52Z

← Older revision		Revision as of 13:01, 31 March 2010
Line 52:		Line 52:

	==Motivation under this article==		==Motivation under this article==
	The article tries to clarify what the switch does and what it does not. ~~Just~~ like [[Joint_stereo\|joint stereo]] ~~it is frequently misinterpreted~~, and identified with a filter.		The article tries to clarify what the switch does and what it does not. It is frequently misinterpreted, like [[Joint_stereo\|joint stereo]], and identified with a filter.
	In explaining what it does, in easy terms and in technical terms, the reader should get a better understanding of the motivation and the usage of such switch.		In explaining what it does, in easy terms and in technical terms, the reader should get a better understanding of the motivation and the usage of such switch.