OggCELT - Revision history

DavidSchleef: /* Ogg mapping (experimental) */

2009-08-29T23:21:05Z

Ogg mapping (experimental)

← Older revision		Revision as of 23:21, 29 August 2009
Line 78:		Line 78:
	\| header_size \| 32-35		\| header_size \| 32-35
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-	\| ~~mode~~ \| 36-39	+	\| sample_rate \| 36-39
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-	\| ~~sample_rate~~ \| 40-43	+	\| nb_channels \| 40-43
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-	\| ~~nb_channels~~ \| 44-47	+	\| frame_size \| 44-47
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-	\| ~~bytes_per_packet~~ \| 48-51	+	\| overlap \| 48-51
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-	\| ~~extra_headers~~ \| 52-55	+	\| bytes_per_packet \| 52-55
		+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		+	\| extra_headers \| 56-59
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

	[[Category:Ogg Mappings]]		[[Category:Ogg Mappings]]

Jmspeex at 02:15, 31 July 2008

2008-07-31T02:15:16Z

← Older revision		Revision as of 02:15, 31 July 2008
Line 46:		Line 46:

	The resolution is defined in the "frac" array in quant_bands.c. The values themselves are the number of subdivisions to use in 6 dB, i.e. for band i, the resolution used is 6/frac[i] dB. So the higher the value, the more accurate the encoding and the more bits it takes.		The resolution is defined in the "frac" array in quant_bands.c. The values themselves are the number of subdivisions to use in 6 dB, i.e. for band i, the resolution used is 6/frac[i] dB. So the higher the value, the more accurate the encoding and the more bits it takes.
		+
		+	== Design decisions ==
		+
		+	* How do we allocate the fine energy bits?
		+	* Do we have a fixed static bit allocation or do we transmit it in a header?
		+	* Dynamic bit allocation?

	== Ogg mapping (experimental) ==		== Ogg mapping (experimental) ==

Jmspeex at 00:39, 26 April 2008

2008-04-26T00:39:19Z

← Older revision		Revision as of 00:39, 26 April 2008
Line 1:		Line 1:
	__NOTOC__		__NOTOC__
		+	{{draft}}
		+
	CELT is an experimental audio codec for use in low-delay communication.		CELT is an experimental audio codec for use in low-delay communication.

Line 46:		Line 48:

	== Ogg mapping (experimental) ==		== Ogg mapping (experimental) ==
-
-	~~{{draft}}~~

	Default field type: LITTLE ENDIAN unsigned integer		Default field type: LITTLE ENDIAN unsigned integer

Gmaxwell: /* CELT Tuning */

2008-04-25T23:23:03Z

CELT Tuning

← Older revision		Revision as of 23:23, 25 April 2008
Line 19:		Line 19:
	==CELT Tuning==		==CELT Tuning==

-	CELT currently provides three ~~types~~ of tuning ~~knob~~.	+	CELT currently provides three classes of tuning knobs.

-	===~~Spectrum details bit~~ allocation===	+	===Bit allocation for the spectrum details===
	The frequency-dependent allocation of bits used to represent the 'details' of each frame's spectrum is by far the most important set of tuneables in CELT.		The frequency-dependent allocation of bits used to represent the 'details' of each frame's spectrum is by far the most important set of tuneables in CELT.

Line 33:		Line 33:

	===Minimum width of bands===		===Minimum width of bands===
-	At low frequencies, critical bands are too narrow to be useful, so CELT imposes a minimum width for the bands. The minimum width is (in MDCT frequency bins) is defined by MIN_BINS in modes.c. The trade off is that for small values, there will be more bands, so more energy data to encode, while for large values, there may not be enough resolution to encode the spectral shape properly.	+	At low frequencies critical bands are too narrow to be useful so CELT imposes a minimum width for the bands.

-	~~===Energy encoding resolution===~~	+	The minimum width is defined in MDCT frequency bins and is controlled by MIN_BINS in modes.c.

-	The last set of parameters is the resolution of the quantizer used to encode the 'shape' of the spectrum of every frame. Ideally the shape of the spectrum would be encoded as as accurately as possible, but every bit used to accurately represent the shape of the spectrum is unavailable to represent the spectrum details. The ~~ear's~~ sensitivity to the exact amount of energy in a critical band is limited, especially at higher frequencies.	+	If MIN_BINS is set to a small value there will be more bands and as a result more energy data to encode which hurts the encoder's efficiency. If MIN_BINS is set to a large value there may not be enough frequency-resolution to encode the spectral shape in a manner which conforms well to human perception.
		+
		+	===Band energy resolution===
		+
		+	The last set of parameters is the resolution of the quantizer used to encode the 'shape' of the spectrum of every frame. Ideally the shape of the spectrum would be encoded as as accurately as possible, but every bit used to accurately represent the shape of the spectrum is unavailable to represent the spectrum details. The sensitivity of the human perceptual system to the exact amount of energy in a critical band is limited, especially at higher frequencies.

	The resolution is defined in the "frac" array in quant_bands.c. The values themselves are the number of subdivisions to use in 6 dB, i.e. for band i, the resolution used is 6/frac[i] dB. So the higher the value, the more accurate the encoding and the more bits it takes.		The resolution is defined in the "frac" array in quant_bands.c. The values themselves are the number of subdivisions to use in 6 dB, i.e. for band i, the resolution used is 6/frac[i] dB. So the higher the value, the more accurate the encoding and the more bits it takes.

Gmaxwell: no toc

2008-04-25T23:18:15Z

no toc

← Older revision		Revision as of 23:18, 25 April 2008
Line 1:		Line 1:
		+	__NOTOC__
	CELT is an experimental audio codec for use in low-delay communication.		CELT is an experimental audio codec for use in low-delay communication.

Gmaxwell: /* Frequency-dependent bit allocation */

2008-04-25T23:16:06Z

Frequency-dependent bit allocation

← Older revision		Revision as of 23:16, 25 April 2008
Line 20:		Line 20:
	CELT currently provides three types of tuning knob.		CELT currently provides three types of tuning knob.

-	===~~Frequency-dependent~~ bit allocation===	+	===Spectrum details bit allocation===
-	~~This~~ is by far the most important ~~thing to tune~~. There's a matrix in modes.c called "band_allocation". It has BITALLOC_SIZE lines and BARK_BANDS columns. Each line determines how many bits will be allocated to each critical band ~~depending on the number of bits available~~.	+	The frequency-dependent allocation of bits used to represent the 'details' of each frame's spectrum is by far the most important set of tuneables in CELT.
		+
		+	There is a matrix in modes.c called "band_allocation". It has BITALLOC_SIZE lines and BARK_BANDS columns. Each line determines how many bits will be allocated to each critical band.

	Even in CBR mode (the only mode currently supported) the available number of bits will change from frame to frame because the space consumed by the compressed spectral envelope is not constant. However, at a single constant bitrate the available number of bits does not change tremendously much from frame to frame, as a result most of the values in the matrix will have little to no effect at any particular bit-rate setting.		Even in CBR mode (the only mode currently supported) the available number of bits will change from frame to frame because the space consumed by the compressed spectral envelope is not constant. However, at a single constant bitrate the available number of bits does not change tremendously much from frame to frame, as a result most of the values in the matrix will have little to no effect at any particular bit-rate setting.

Gmaxwell: /* Energy encoding resolution */

2008-04-25T23:09:48Z

Energy encoding resolution

← Older revision		Revision as of 23:09, 25 April 2008
Line 33:		Line 33:

	===Energy encoding resolution===		===Energy encoding resolution===
-	The last set of parameters is the resolution ~~at which~~ the ~~energy is encoded~~. ~~The trade off here is that any bit spent on encoding~~ the ~~energy more~~ accurately ~~isn~~'~~t spent on~~ the ~~residual signal~~ in 1). The resolution is defined in the "frac" array in quant_bands.c. The values themselves are the number of subdivisions to use in 6 dB, i.e. for band i, the resolution used is 6/frac[i] dB. So the higher the value, the more accurate the encoding and the more bits it takes.	+
		+	The last set of parameters is the resolution of the quantizer used to encode the 'shape' of the spectrum of every frame. Ideally the shape of the spectrum would be encoded as as accurately as possible, but every bit used to accurately represent the shape of the spectrum is unavailable to represent the spectrum details. The ear's sensitivity to the exact amount of energy in a critical band is limited, especially at higher frequencies.
		+
		+	The resolution is defined in the "frac" array in quant_bands.c. The values themselves are the number of subdivisions to use in 6 dB, i.e. for band i, the resolution used is 6/frac[i] dB. So the higher the value, the more accurate the encoding and the more bits it takes.

	== Ogg mapping (experimental) ==		== Ogg mapping (experimental) ==

Gmaxwell: /* Frequency-dependent bit allocation */

2008-04-25T23:01:39Z

Frequency-dependent bit allocation

← Older revision		Revision as of 23:01, 25 April 2008
Line 21:		Line 21:

	===Frequency-dependent bit allocation===		===Frequency-dependent bit allocation===
-	This is by far the most important thing to tune. There's a matrix in modes.c called "band_allocation". It has BITALLOC_SIZE lines and BARK_BANDS columns. Each line determines how many bits will be allocated to each critical band at a ~~certain~~ bit-rate.	+	This is by far the most important thing to tune. There's a matrix in modes.c called "band_allocation". It has BITALLOC_SIZE lines and BARK_BANDS columns. Each line determines how many bits will be allocated to each critical band depending on the number of bits available.
		+
		+	Even in CBR mode (the only mode currently supported) the available number of bits will change from frame to frame because the space consumed by the compressed spectral envelope is not constant. However, at a single constant bitrate the available number of bits does not change tremendously much from frame to frame, as a result most of the values in the matrix will have little to no effect at any particular bit-rate setting.
		+
		+	The particular bit-rate that a line is used for is not explicitly specified but is instead inferred by the actual bit consumption of that line.
		+
		+	When the amount of bits available is somewhere between the amounts provided by explicitly configured lines the encoder will interpolate between the two nearest matching lines to achieve the needed bit-rate.

	===Minimum width of bands===		===Minimum width of bands===

Gmaxwell: tuning from JM

2008-04-25T22:33:11Z

tuning from JM

← Older revision		Revision as of 22:33, 25 April 2008
Line 15:		Line 15:

	The [http://www.celt-codec.org/ CELT homepage] has all additional info as well as samples.		The [http://www.celt-codec.org/ CELT homepage] has all additional info as well as samples.
		+
		+	==CELT Tuning==
		+
		+	CELT currently provides three types of tuning knob.
		+
		+	===Frequency-dependent bit allocation===
		+	This is by far the most important thing to tune. There's a matrix in modes.c called "band_allocation". It has BITALLOC_SIZE lines and BARK_BANDS columns. Each line determines how many bits will be allocated to each critical band at a certain bit-rate.
		+
		+	===Minimum width of bands===
		+	At low frequencies, critical bands are too narrow to be useful, so CELT imposes a minimum width for the bands. The minimum width is (in MDCT frequency bins) is defined by MIN_BINS in modes.c. The trade off is that for small values, there will be more bands, so more energy data to encode, while for large values, there may not be enough resolution to encode the spectral shape properly.
		+
		+	===Energy encoding resolution===
		+	The last set of parameters is the resolution at which the energy is encoded. The trade off here is that any bit spent on encoding the energy more accurately isn't spent on the residual signal in 1). The resolution is defined in the "frac" array in quant_bands.c. The values themselves are the number of subdivisions to use in 6 dB, i.e. for band i, the resolution used is 6/frac[i] dB. So the higher the value, the more accurate the encoding and the more bits it takes.

	== Ogg mapping (experimental) ==		== Ogg mapping (experimental) ==

Gmaxwell at 22:26, 25 April 2008

2008-04-25T22:26:07Z

← Older revision		Revision as of 22:26, 25 April 2008
Line 1:		Line 1:
	CELT is an experimental audio codec for use in low-delay communication.		CELT is an experimental audio codec for use in low-delay communication.
-	The [http://www.celt-codec.org/ CELT homepage] has all ~~the project~~ info.	+
		+	The name stands for "Code-Excited Lapped Transform". It applies some of the [[Wikipedia:CELP\|CELP]] principles, but does everything in the frequency domain, which removes some of the limitations of CELP.
		+
		+	The CELT codec is meant to close the gap between [[Vorbis]] and [[Speex]] for applications where both high quality audio and low delay are desired. It is a
		+
		+	Current features include:
		+
		+	* '''Ultra-low latency (typically from 3 to 9 ms)'''
		+	* Full audio bandwidth (44.1 kHz and 48 kHz)
		+	* Stereo support
		+	* Packet loss concealment
		+	* Constant bit-rates from 32 kbps to 128 kbps and above
		+	* A fixed-point version of the encoder and decoder
		+
		+	The [http://www.celt-codec.org/ CELT homepage] has all additional info as well as samples.

	== Ogg mapping (experimental) ==		== Ogg mapping (experimental) ==