Block switching - Revision history

Speckmade at 16:46, 14 June 2007

2007-06-14T16:46:23Z

← Older revision		Revision as of 16:46, 14 June 2007
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	The Psychoacoustic model decides when to '''switch''' to short blocks and back to long blocks (block switching).		The Psychoacoustic model decides when to '''switch''' to short blocks and back to long blocks (block switching).

	In [[MP3]], switching to short blocks will isolate the attack to 192 sample window, so the oscillations are only spread over 192 samples instead of 576. Block switching is also used by [[~~Ogg~~ Vorbis]] and [[AAC]], ''(except on windows that can be a power of two only)''. [[~~MPC~~]], being a [[subband~~\|subband coder~~]] doesn't make use of block switching, ''(although it is implemented and can be used)''		In [[MP3]], switching to short blocks will isolate the attack to 192 sample window, so the oscillations are only spread over 192 samples instead of 576. Block switching is also used by (Ogg) [[Vorbis]] and [[Advanced Audio Coding\|AAC]], ''(except on windows that can be a power of two only)''. [[Musepack]], being a [[subband]] coder doesn't make use of block switching, ''(although it is implemented and can be used)''

	Switching to short blocks and increasing of the [[bitrate]] to encode a series of [[MDCT]] coefficients of a particular [[transient]] is one way to combat [[Pre echo]].		Switching to short blocks and increasing of the [[bitrate]] to encode a series of [[Modified Discrete Cosine Transform\|MDCT]] coefficients of a particular [[transient]] is one way to combat [[Pre echo]].

	==Long & Short Blocks==		== Long & Short Blocks ==
	Audio encoding systems will commonly summarise the sound energy in one small stretch of time at a time. The duration of a single summarisation is also called a [[window]] and once a window of sound has been quantised, selected and packed, it can be considered as an individual '''block''' of audio information to be finaly stored in a frame.		Audio encoding systems will commonly summarise the sound energy in one small stretch of time at a time. The duration of a single summarisation is also called a [[window]] and once a window of sound has been quantised, selected and packed, it can be considered as an individual '''block''' of audio information to be finaly stored in a frame.

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	[[LAME]] has only two block sizes available, long blocks and short blocks. In Lame's case Short blocks require more data to describe less time than Long blocks so they are only selected when they significantly improve the alignment of transformation windows to audio details.		[[LAME]] has only two block sizes available, long blocks and short blocks. In Lame's case Short blocks require more data to describe less time than Long blocks so they are only selected when they significantly improve the alignment of transformation windows to audio details.

	==Additional reading==		== Additional reading ==
			Some Java applets to examine fourier series behaviour (note that [[Modified Discrete Cosine Transform\|MDCT]] behaviour is not totally identical):
	Some Java applets to examine fourier series behaviour (note that [[MDCT]] behaviour is not totally identical):

	*; http://www.jhu.edu/~signals/fourier2/ : You can draw a sharp attack here, and use calculate with a large number of coefficients... if you start to reduce the number of coefficients you will see the [[pre echo]] appear.		*; http://www.jhu.edu/~signals/fourier2/ : You can draw a sharp attack here, and use calculate with a large number of coefficients... if you start to reduce the number of coefficients you will see the [[pre echo]] appear.

	*; http://www.gac.edu/~huber/fourier : Doesnt seem to work in netscape. iirc this one lets you listen to the sound.		*; http://www.gac.edu/~huber/fourier : Doesnt seem to work in netscape. iirc this one lets you listen to the sound.

	*; http://www.univie.ac.at/future.media/moe/galerie/fourier/fourier.html : Maths online fourier series applet.		*; http://www.univie.ac.at/future.media/moe/galerie/fourier/fourier.html : Maths online fourier series applet.


	[[Category:Technical]]		[[Category:Technical]]

Pepoluan: Category:Technical

2006-09-11T16:06:20Z

Category:Technical

← Older revision		Revision as of 16:06, 11 September 2006
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	*; http://www.univie.ac.at/future.media/moe/galerie/fourier/fourier.html : Maths online fourier series applet.		*; http://www.univie.ac.at/future.media/moe/galerie/fourier/fourier.html : Maths online fourier series applet.


			[[Category:Technical]]

Pepoluan: minor formatting

2006-09-11T15:42:53Z

minor formatting

← Older revision		Revision as of 15:42, 11 September 2006
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	Switching to short blocks and increasing of the [[bitrate]] to encode a series of [[MDCT]] coefficients of a particular [[transient]] is one way to combat [[Pre echo]].		Switching to short blocks and increasing of the [[bitrate]] to encode a series of [[MDCT]] coefficients of a particular [[transient]] is one way to combat [[Pre echo]].

	==Long ~~blocks~~==		==Long & Short Blocks==
	Audio encoding systems will commonly summarise the sound energy in one small stretch of time at a time. The duration of a single summarisation is also called a [[window]] and once a window of sound has been quantised, selected and packed, it can be considered as an individual block of audio information to be finaly stored in a frame.		Audio encoding systems will commonly summarise the sound energy in one small stretch of time at a time. The duration of a single summarisation is also called a [[window]] and once a window of sound has been quantised, selected and packed, it can be considered as an individual '''block''' of audio information to be finaly stored in a frame.

	Available mathematics used to summarise one block at a time can struggle with evenly representing details throughout a window's duration. There may be a tendency to mirror features at the start of the window onto the other end of the window, or the ends of the window might be the most efficient place to have details occur, it will depend on the particular mathematical transformation used.		Available mathematics used to summarise one block at a time can struggle with evenly representing details throughout a window's duration. There may be a tendency to mirror features at the start of the window onto the other end of the window, or the ends of the window might be the most efficient place to have details occur, it will depend on the particular mathematical transformation used.

Kjoonlee: Del merge templates

2006-09-11T15:01:30Z

Del merge templates

← Older revision		Revision as of 15:01, 11 September 2006
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	~~{{merge-from\|Short block}}~~		The Psychoacoustic model decides when to '''switch''' to short blocks and back to long blocks (block switching).
	~~{{merge-from\|Long block}}~~

	The Psychoacoustic model decides when to switch to short blocks and back to long blocks (block switching).

	In [[MP3]], switching to short blocks will isolate the attack to 192 sample window, so the oscillations are only spread over 192 samples instead of 576. Block switching is also used by [[Ogg Vorbis]] and [[AAC]], ''(except on windows that can be a power of two only)''. [[MPC]], being a [[subband\|subband coder]] doesn't make use of block switching, ''(although it is implemented and can be used)''		In [[MP3]], switching to short blocks will isolate the attack to 192 sample window, so the oscillations are only spread over 192 samples instead of 576. Block switching is also used by [[Ogg Vorbis]] and [[AAC]], ''(except on windows that can be a power of two only)''. [[MPC]], being a [[subband\|subband coder]] doesn't make use of block switching, ''(although it is implemented and can be used)''

Kjoonlee: simple merge from old version of Long block

2006-09-11T14:59:44Z

simple merge from old version of Long block

← Older revision		Revision as of 14:59, 11 September 2006
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	Switching to short blocks and increasing of the [[bitrate]] to encode a series of [[MDCT]] coefficients of a particular [[transient]] is one way to combat [[Pre echo]].		Switching to short blocks and increasing of the [[bitrate]] to encode a series of [[MDCT]] coefficients of a particular [[transient]] is one way to combat [[Pre echo]].

	=Additional reading:=		==Long blocks==
			Audio encoding systems will commonly summarise the sound energy in one small stretch of time at a time. The duration of a single summarisation is also called a [[window]] and once a window of sound has been quantised, selected and packed, it can be considered as an individual block of audio information to be finaly stored in a frame.

			Available mathematics used to summarise one block at a time can struggle with evenly representing details throughout a window's duration. There may be a tendency to mirror features at the start of the window onto the other end of the window, or the ends of the window might be the most efficient place to have details occur, it will depend on the particular mathematical transformation used.
			With such variance in transformation accuracy throughout each block, varying the size of blocks to best fit over the actual details present in the audio stream increases the overall accuracy of the encoding.

			[[LAME]] has only two block sizes available, long blocks and short blocks. In Lame's case Short blocks require more data to describe less time than Long blocks so they are only selected when they significantly improve the alignment of transformation windows to audio details.

			==Additional reading==

	Some Java applets to examine fourier series behaviour (note that [[MDCT]] behaviour is not totally identical):		Some Java applets to examine fourier series behaviour (note that [[MDCT]] behaviour is not totally identical):

Pepoluan: SUGGEST: MERGE-FROM (2)

2006-09-09T07:37:13Z

SUGGEST: MERGE-FROM (2)

← Older revision		Revision as of 07:37, 9 September 2006
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			{{merge-from\|Short block}}
			{{merge-from\|Long block}}

	The Psychoacoustic model decides when to switch to short blocks and back to long blocks (block switching).		The Psychoacoustic model decides when to switch to short blocks and back to long blocks (block switching).

HotshotGG: /* Additional reading: */

2005-06-27T05:12:52Z

Additional reading:

← Older revision		Revision as of 05:12, 27 June 2005
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	Switching to short blocks and increasing of the [[bitrate]] to encode a series of [[MDCT]] coefficients of a particular [[transient]] is one way to combat [[Pre echo]].		Switching to short blocks and increasing of the [[bitrate]] to encode a series of [[MDCT]] coefficients of a particular [[transient]] is one way to combat [[Pre echo]].

	==Additional reading:==		=Additional reading:=

	Some Java applets to examine fourier series behaviour (note that [[MDCT]] behaviour is not totally identical):		Some Java applets to examine fourier series behaviour (note that [[MDCT]] behaviour is not totally identical):

HotshotGG: Some minor grammer corrections and wording. The applets are good example? but the link to the first one should be on the page about pre-echo.

2005-06-27T03:13:10Z

Some minor grammer corrections and wording. The applets are good example? but the link to the first one should be on the page about pre-echo.

← Older revision		Revision as of 03:13, 27 June 2005
Line 1:		Line 1:
	~~Psycoacoustic~~ model decides when to switch to short blocks and back to long blocks (block switching).		The Psychoacoustic model decides when to switch to short blocks and back to long blocks (block switching).

	In [[MP3]], switching to short blocks will isolate the attack to 192 sample window, so the oscillations are only spread over 192 samples instead of 576. Block switching is also used by [[Ogg Vorbis]] and [[AAC]]. ~~but~~ [[MPC]], being a [[subband\|subband coder]] doesn't ~~need~~ it.		In [[MP3]], switching to short blocks will isolate the attack to 192 sample window, so the oscillations are only spread over 192 samples instead of 576. Block switching is also used by [[Ogg Vorbis]] and [[AAC]], ''(except on windows that can be a power of two only)''. [[MPC]], being a [[subband\|subband coder]] doesn't make use of block switching, ''(although it is implemented and can be used)''

	Switching to short blocks and increasing of the [[bitrate]] to encode ~~lots~~ of [[MDCT]] coefficients of a transient ~~are the 2 main ways~~ to combat [[Pre echo]].		Switching to short blocks and increasing of the [[bitrate]] to encode a series of [[MDCT]] coefficients of a particular [[transient]] is one way to combat [[Pre echo]].

	~~Java applets to examine fourier series behaviour (note that [[MDCT]] behaviour is not totally identical)~~:		==Additional reading:==

	~~; http://www.jhu.edu/~signals/fourier2/ : You can draw a sharp attack here, and use calculate with a large number of coefficients... if you start~~ to ~~reduce the number of coefficients you will see the~~ [[~~pre echo~~]] ~~appear.~~		Some Java applets to examine fourier series behaviour (note that [[MDCT]] behaviour is not totally identical):

	; http://www.~~gac~~.edu/~~~huber~~/~~fourier~~ : ~~Doesnt seem to work in netscape~~. ~~iirc this one lets~~ you ~~listen~~ to the ~~sound~~.		*; http://www.jhu.edu/~signals/fourier2/ : You can draw a sharp attack here, and use calculate with a large number of coefficients... if you start to reduce the number of coefficients you will see the [[pre echo]] appear.

	; http://www.univie.ac.at/future.media/moe/galerie/fourier/fourier.html : Maths online fourier series applet.		*; http://www.gac.edu/~huber/fourier : Doesnt seem to work in netscape. iirc this one lets you listen to the sound.

			*; http://www.univie.ac.at/future.media/moe/galerie/fourier/fourier.html : Maths online fourier series applet.

Jan at 11:43, 22 March 2005

2005-03-22T11:43:41Z

New page

Psycoacoustic model decides when to switch to short blocks and back to long blocks (block switching).

In [[MP3]], switching to short blocks will isolate the attack to 192 sample window, so the oscillations are only spread over 192 samples instead of 576. Block switching is also used by [[Ogg Vorbis]] and [[AAC]]. but [[MPC]], being a [[subband|subband coder]] doesn't need it.

Switching to short blocks and increasing of the [[bitrate]] to encode lots of [[MDCT]] coefficients of a transient are the 2 main ways to combat [[Pre echo]].

Java applets to examine fourier series behaviour (note that [[MDCT]] behaviour is not totally identical):

; http://www.jhu.edu/~signals/fourier2/ : You can draw a sharp attack here, and use calculate with a large number of coefficients... if you start to reduce the number of coefficients you will see the [[pre echo]] appear.

; http://www.gac.edu/~huber/fourier : Doesnt seem to work in netscape. iirc this one lets you listen to the sound.

; http://www.univie.ac.at/future.media/moe/galerie/fourier/fourier.html : Maths online fourier series applet.