Aufgaben:Exercise 3.6: Adaptive Multi Rate Codec - Revision history

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	[[Category:Examples of Communication Systems: Exercises\|^3.3 Speech Coding^]]		[[Category:Examples of Communication Systems: Exercises\|^3.3 Speech Coding^]]
	[[de:Aufgaben:3.~~6_Adaptive_Multi–Rate_Codec~~]]		[[de:Aufgaben:Aufgabe 3.6: Adaptive Multi–Rate Codec]]

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	[[Category:Examples of Communication Systems: Exercises\|^3.3 Speech Coding^]]		[[Category:Examples of Communication Systems: Exercises\|^3.3 Speech Coding^]]
			[[de:Aufgaben:3.6_Adaptive_Multi–Rate_Codec]]

Guenter at 12:58, 25 January 2023

2023-01-25T12:58:26Z

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	'''(1)'''  With the data rate $12.2 \ \rm kbit/s$, exactly $\underline{244 \ \rm ~~bit~~}$ results within $20 \ \rm ms$, while ~~for example~~ in $4.75 \ \rm kbit/s$ mode only $95 \ \rm ~~bit~~$ is transmitted.		'''(1)'''  With the data rate  $R_{\rm C} = 12.2 \ \rm kbit/s$,  exactly  $\underline{244 \ \rm bits}$  results within  $20 \ \rm ms$,  while e.g. in  $4.75 \ \rm kbit/s$  mode only  $95 \ \rm bits$  are transmitted.


	'''(2)'''  In each subframe, the FCB pulse requires $35 \ \rm ~~bit~~$ (five tracks of seven bits each) and the FCB gain requires five bits.		'''(2)'''  In each subframe,  the FCB pulse requires  $35 \ \rm bits$  (five tracks of seven bits each)  and the FCB gain requires five bits.
	*With four subframes, this gives $N_{\rm FCB} \underline{= 160 \ \rm bits}$.

			*With four subframes,  this gives $N_{\rm FCB} \hspace{0.15cm}\underline{= 160 \ \rm bits}$.


	~~'''(3)'''  This leaves the difference from (1) and (2), i.e. $N_{\rm LPC/LTP}\underline{ = 84 \rm bits}$.~~

			'''(3)'''  This leaves the difference from  '''(1)'''  and  '''(2)''',  i.e. $N_{\rm LPC/LTP}\hspace{0.15cm} \underline{ = 84\ \rm bits}$.

	~~'''(4)'''  The sign bit "$0$" indicates a negative first pulse.~~
	*Because $001 < 011$, the second pulse has the same sign.
	*The two amounts result in
	~~:$$\|N_1\| \ = \ 3 \hspace{0.1cm}{\rm(da \hspace{0.1cm} track \hspace{0.1cm}3)} + 5\cdot 1 \hspace{0.1cm} {\rm(bit\:specification \hspace{0.1cm} 001)} = 8\hspace{0.05cm}, $$~~
	~~:$$ \|N_2\| \ = \ 3 \hspace{0.1cm}{\rm(da \hspace{0.1cm} track \hspace{0.1cm}3)} + 5\cdot 3 \hspace{0.1cm} {\rm(bit\:specification \hspace{0.1cm} 011)} = 18\hspace{0.05cm}.$$~~
	*Therefore, to be entered for the third track is $N_{1} \underline{ = -8}$ and $N_{2} \underline{ = -18}.$

			'''(4)'''  The sign bit  "$0$"  indicates a negative first pulse.
			*Because  $001 < 011$,  the second pulse has the same sign.

			*The two magnitudes result in
			:$$\|N_1\| \ = \ 3 \hspace{0.1cm}{\rm(since \hspace{0.1cm} track \hspace{0.1cm}3)} + 5\cdot 1 \hspace{0.1cm} {\rm(bit\:specification \hspace{0.1cm} 001)} = 8\hspace{0.05cm}, $$
			:$$ \|N_2\| \ = \ 3 \hspace{0.1cm}{\rm(since \hspace{0.1cm} track \hspace{0.1cm}3)} + 5\cdot 3 \hspace{0.1cm} {\rm(bit\:specification \hspace{0.1cm} 011)} = 18\hspace{0.05cm}.$$
			*Therefore,  to be entered for the third track is  $N_{1}\hspace{0.15cm} \underline{ = -8}$  and  $N_{2} \hspace{0.15cm}\underline{ = -18}.$

	~~'''(5)'''  In an analogous way, for track $4$ we obtain the values  $N_{1} \underline{ = +39}$  and  $N_{2} \underline{ = -14}$.~~

			'''(5)'''  In an analogous way,  for track  $4$  we obtain the values  $N_{1}\hspace{0.15cm} \underline{ = +39}$  and  $N_{2}\hspace{0.15cm} \underline{ = -14}$.

	'''(6)'''  The fifth track provides  $N_{1} \underline{ =-30}$  and  $N_{2} \underline{ = +5}$
			'''(6)'''  The fifth track provides  $N_{1}\hspace{0.15cm} \underline{ =-30}$  and  $N_{2}\hspace{0.15cm} \underline{ = +5}$

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Guenter at 12:43, 25 January 2023

2023-01-25T12:43:43Z

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	In the late 1990s,  a very flexible,  adaptive speech codec was developed and standardized in the form of  $\rm AMR$  codec.  This provides a total of eight different modes with data rates between  $4.75 \ \rm kbit/s$  and  $12.2 \ \rm kbit/s$.		In the late 1990s,  a very flexible,  adaptive speech codec was developed and standardized in the form of  $\rm AMR$  codec.  This provides a total of eight different modes with data rates between  $4.75 \ \rm kbit/s$  and  $12.2 \ \rm kbit/s$.

	The AMR codec,  like the full rate codec  $\rm (FRC)$  discussed in  [[Aufgaben:Exercise_3.5:~~_GSM_Full-Rate_Voice_Codec~~\|$\text{Exercise 3.5}$]],  includes both a short-term prediction  $\rm (LPC)$  and a long-term prediction  $\rm (LTP)$.  However,  these two components are realized differently from FRC.		The AMR codec,  like the full rate codec  $\rm (FRC)$  discussed in  [[Aufgaben:Exercise_3.5:_GSM_Full_Rate_Vocoder\|$\text{Exercise 3.5}$]],  includes both a short-term prediction  $\rm (LPC)$  and a long-term prediction  $\rm (LTP)$.  However,  these two components are realized differently from FRC.

	The main difference between AMR and FRC is the encoding of the residual signal  $($after LPC and LTP$)$:		The main difference between AMR and FRC is the encoding of the residual signal  $($after LPC and LTP$)$:

Guenter at 12:42, 25 January 2023

2023-01-25T12:42:17Z

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	⇒   '''Track 1'''  includes		⇒   '''Track 1'''  includes
	#a positive pulse  $({\rm sign} = 1)$  at position  $\big [1$  (first possible position for track 1)  $\hspace{0.02cm}\text{plus}\hspace{0.2cm}0$ (bit specification for  "000") $= 1\big]$,		#a positive pulse  $({\rm sign} = 1)$  at position  $\big [1$  (first possible position for track 1)  $\hspace{0.02cm}\text{plus}\hspace{0.2cm}0$  (bit specification for  "000") $= 1\big]$,
	#another positive pulse  $($since $110 > 000)$  at position  $\big [1 \hspace{0.2cm}\text{plus}\hspace{0.2cm}5$ (pulse spacing in each track) $\hspace{0.~~2cm~~}\text{~~mal~~}\hspace{0.2cm}6$ (bit specification for " 110") = $31\hspace{0.05cm}.$		#another positive pulse  $($since $110 > 000)$  at position  $\big [1 \hspace{0.2cm}\text{plus}\hspace{0.2cm}5$ (pulse spacing in each track) $\hspace{0.02cm}\text{times}\hspace{0.2cm}6$  (bit specification for " 110") = $31\hspace{0.05cm}\big].$


	'''Track 2''' includes.		'''Track 2''' includes.
	*a negative pulse (${\rm VZ} = 0$) at $2$ (first possible position for track 2) $\hspace{0.~~2cm~~}\text{plus}\hspace{0.2cm}5\hspace{0.2cm}\text{~~mal~~}\hspace{0.2cm}4$ (bit specification for " 100") = $22\hspace{0.05cm},$		#a negative pulse (${\rm sign} = 0$)  at position  $\big [2$ (first possible position for track 2)  $\hspace{0.02cm}\text{plus}\hspace{0.2cm}5\hspace{0.2cm}\text{times}\hspace{0.2cm}4$  (bit specification for  " 100")  $=22\hspace{0.05cm}\big],$
	*a positive pulse (sign reversal due to $011 > 100$) at position $2 \hspace{0.2cm}\text{plus}\hspace{0.2cm}5\hspace{0.2cm}\text{~~mal~~}\hspace{0.2cm}3$ (bit specification for " 011") = $17\hspace{0.05cm}.$		#a positive pulse  $($sign reversal due to  $011 > 100)$  at position  $\big [2 \hspace{0.2cm}\text{plus}\hspace{0.2cm}5\hspace{0.2cm}\text{times}\hspace{0.2cm}3$  (bit specification for  " 011")  $=17\hspace{0.05cm}\big].$


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	Hint:		<u>Hint:</u>

	*This exercise belongs to the chapter  [[Examples_of_Communication_Systems/Voice_Coding\|"Speech Coding"]].		*This exercise belongs to the chapter  [[Examples_of_Communication_Systems/Voice_Coding\|"Speech Coding"]].

	*When entering the pulse positions  $N_{1}$  denotes the first triple of bits and  $N_{2}$  the second.		*When entering the pulse positions  $N_{1}$  denotes the first triple of bits and  $N_{2}$  the second.
	*For example, for track  $2$  one would have to enter the values  $N_{1}=-22$  and  $N_{2}=+17$~~ ~~.
			*For example,  for track  $2$  one would have to enter the values  $N_{1}=-22$  and  $N_{2}=+17$.


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	{How many bits describe a speech frame $($of duration  $20 \ \rm ms)$  in  $12.2 \ \rm kbit/s$ mode?		{How many bits describe a speech frame $($of duration  $20 \ \rm ms)$  in  $12.2 \ \rm kbit/s$ mode?
	\|type="{}"}		\|type="{}"}
	$N_{12.2} \ = \ $ { 244 3% } $ \ \rm ~~Bit~~$		$N_{12.2} \ = \ $ { 244 3% } $ \ \rm bits$

	{How many bits are needed for FCB pulse and gain per frame?		{How many bits are needed for FCB pulse and gain per frame?
	\|type="{}"}		\|type="{}"}
	$N_{\rm FCB} \ = \ $ { 160 3% } $ \ \rm ~~Bit~~$		$N_{\rm FCB} \ = \ $ { 160 3% } $ \ \rm bits$

	{ How many bits are left for LPC and LTP?		{ How many bits are left for LPC and LTP?
	\|type="{}"}		\|type="{}"}
	$N_{\rm LPC/LTP} \ = \ $ { 84 3% } $ \ \rm ~~Bit~~$		$N_{\rm LPC/LTP} \ = \ $ { 84 3% } $ \ \rm bits$

	{What subframe pulse positions and signs does track  $3$ describe? ~~<br>~~Follow the instructions for input on the ~~input~~ page.		{What subframe pulse positions and signs does track  $3$  describe?  Follow the instructions for input on the information page.
	\|type="{}"}		\|type="{}"}
	$N_{1} \ = \ $ { -8.24--7.76 }		$N_{1} \ = \ $ { -8.24--7.76 }

Guenter at 11:56, 25 January 2023

2023-01-25T11:56:12Z

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	[[File:En_Bei_A_3_6.png\|right\|frame\|Tracks of the AMR codec]]		[[File:En_Bei_A_3_6.png\|right\|frame\|Tracks of the AMR codec]]
	In the late 1990s, a very flexible, adaptive speech codec was developed and ~~standardised~~ in the form of ~~the~~ AMR codec. This provides a total of eight different modes with data rates between  $4.75 \ \rm kbit/s$  and  $12.2 \ \rm kbit/s$~~ ~~.		In the late 1990s,  a very flexible,  adaptive speech codec was developed and standardized in the form of  $\rm AMR$  codec.  This provides a total of eight different modes with data rates between  $4.75 \ \rm kbit/s$  and  $12.2 \ \rm kbit/s$.

	The AMR codec, like the full rate codec (FRC) discussed in  [[Aufgaben:Exercise_3.5:_GSM_Full-Rate_Voice_Codec\|"Exercise 3.5"]] , includes both a short-term prediction (LPC) and a long-term prediction (LTP). However, these two components are ~~realised~~ differently from FRC.		The AMR codec,  like the full rate codec  $\rm (FRC)$  discussed in  [[Aufgaben:Exercise_3.5:_GSM_Full-Rate_Voice_Codec\|$\text{Exercise 3.5}$]],  includes both a short-term prediction  $\rm (LPC)$  and a long-term prediction  $\rm (LTP)$.  However,  these two components are realized differently from FRC.

	The main difference between AMR and FRC is the ~~coding~~ of the residual signal (after LPC and LTP):		The main difference between AMR and FRC is the encoding of the residual signal  $($after LPC and LTP$)$:
	*Instead of "Regular Pulse Excitation" (RPE), the "Algebraic Code Excitation Linear Prediction" (ACELP) ~~procedure~~ is used ~~for the AMR code~~.		#Instead of  "Regular Pulse Excitation"  $\rm (RPE)$,  here the  "Algebraic Code Excitation Linear Prediction"  $\rm (ACELP)$  is used.
	*From the fixed ~~codebook~~ (FCB), for each subframe of  $5 \ \rm ms$  duration, the FCB pulse and FCB gain that best match the residual signal (for which the mean square error of the difference signal becomes minimum) is selected.		#From the fixed code book  $\rm (FCB)$,  for each subframe of  $5 \ \rm ms$  duration,  the  "FCB pulse"  and the  "FCB gain"  that best match the residual signal  $($for which the mean square error of the difference signal becomes minimum$)$  is selected.


	Each entry in the fixed ~~codebook~~ identifies a pulse where exactly  $10$  of  $40$  positions are occupied by  $\pm1$~~ . In this regard it should be noted:~~		Each entry in the fixed code book identifies a pulse where exactly  $10$  of  $40$  positions are occupied by  $\pm1$.
	*The pulse is divided into five tracks with eight possible positions each, where track  $1$  contains the positions  $1,\ 6,\ 11$, ... , $36$  of the subframe and track  $5$  the positions  $5,\ 10,\ 15$, ... ~~, $40$~~  ~~describes.~~
	*In each track there are exactly two values  $\pm1$, while all the other six values are  $0$ . The two  $±1$-positions are each assigned three bits - i.e. with  $000$, ... ,  $111$ - are coded.
	*Another bit is used for the sign of the first-mentioned pulse, where a "$1$" indicates a positive sign and a "$0$" a negative sign.
	*If the pulse position of the second pulse is greater than that of the first pulse, the second pulse has the same sign as the first, otherwise the opposite.
	*Thus, seven bits per track are transmitted to the receiver, plus five bits for the so-called ''FCB amplification''.

			In this regard it should be noted:
			*The pulse is divided into five tracks with eight possible positions each, where track  $1$  contains the positions  $1,\ 6,\ 11$, ... , $36$  of the subframe and track  $5$  describes the positions  $5,\ 10,\ 15$, ... , $40$.

	In the diagram, the  $35$  bits describing an FCB pulse are given as an example.		*In each track there are exactly two values  $\pm1$,  while all the other six values are  zero.

			*The two  $±1$-positions are each assigned three bits –   i.e. encoded with  "$000$", ... ,  "$111$".

			*Another bit is used for the  "sign of the first-mentioned pulse",  where a  "$1$"  indicates a positive sign and a  "$0$"  a negative sign.

			*If the pulse position of the second pulse is greater than that of the first pulse,  the second pulse has the same sign as the first,  otherwise the opposite.

			*Thus,  seven bits per track are transmitted to the receiver,  plus five bits for the so-called  "FCB amplification''.


			In the diagram,  the  $35$  bits describing an FCB pulse are given as an example:

	'''Track 1''' includes.		⇒   '''Track 1'''  includes
	*a positive pulse  $({\rm VZ} = 1)$  at  $1$  (first possible position for track 1)  $\hspace{0.~~2cm~~}\text{plus}\hspace{0.2cm}0$ (bit specification for " 000") $= 1$,		#a positive pulse  $({\rm sign} = 1)$  at position  $\big [1$  (first possible position for track 1)  $\hspace{0.02cm}\text{plus}\hspace{0.2cm}0$ (bit specification for  "000") $= 1\big]$,
	*another positive pulse (since $110 > 000$) at position $1 \hspace{0.2cm}\text{plus}\hspace{0.2cm}5$ (pulse spacing in each track) $\hspace{0.2cm}\text{mal}\hspace{0.2cm}6$ (bit specification for " 110") = $31\hspace{0.05cm}.$		#another positive pulse  $($since $110 > 000)$  at position  $\big [1 \hspace{0.2cm}\text{plus}\hspace{0.2cm}5$ (pulse spacing in each track) $\hspace{0.2cm}\text{mal}\hspace{0.2cm}6$ (bit specification for " 110") = $31\hspace{0.05cm}.$

Guenter: Guenter moved page Aufgaben:Exercise 3.6: Adaptive Multi–Rate Codec to Aufgaben:Exercise 3.6: Adaptive Multi Rate Codec

2023-01-25T09:02:02Z

Guenter moved page Aufgaben:Exercise 3.6: Adaptive Multi–Rate Codec to Aufgaben:Exercise 3.6: Adaptive Multi Rate Codec

← Older revision	Revision as of 11:02, 25 January 2023
(No difference)

Hwang at 15:39, 23 January 2023

2023-01-23T15:39:49Z

← Older revision		Revision as of 17:39, 23 January 2023
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	[[Category:Examples of Communication Systems: Exercises\|^3.3 ~~Voice~~ Coding^]]		[[Category:Examples of Communication Systems: Exercises\|^3.3 Speech Coding^]]

Hwang at 11:35, 23 January 2023

2023-01-23T11:35:26Z

← Older revision		Revision as of 13:35, 23 January 2023
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	In the late 1990s, a very flexible, adaptive speech codec was developed and standardised in the form of the AMR codec. This provides a total of eight different modes with data rates between  $4.75 \ \rm kbit/s$  and  $12.2 \ \rm kbit/s$ .		In the late 1990s, a very flexible, adaptive speech codec was developed and standardised in the form of the AMR codec. This provides a total of eight different modes with data rates between  $4.75 \ \rm kbit/s$  and  $12.2 \ \rm kbit/s$ .

	The AMR codec, like the full-rate codec (FRC) discussed in  [[Aufgaben:Exercise_3.5:_GSM_Full-Rate_Voice_Codec\|"Exercise 3.5"]] , includes both a short-term prediction (LPC) and a long-term prediction (LTP). However, these two components are realised differently from FRC.		The AMR codec, like the full rate codec (FRC) discussed in  [[Aufgaben:Exercise_3.5:_GSM_Full-Rate_Voice_Codec\|"Exercise 3.5"]] , includes both a short-term prediction (LPC) and a long-term prediction (LTP). However, these two components are realised differently from FRC.

	The main difference between AMR and FRC is the coding of the residual signal (after LPC and LTP):		The main difference between AMR and FRC is the coding of the residual signal (after LPC and LTP):
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	Hint:		Hint:

	*This exercise belongs to the chapter  [[Examples_of_Communication_Systems/Voice_Coding\|"~~Voice~~ Coding"]].		*This exercise belongs to the chapter  [[Examples_of_Communication_Systems/Voice_Coding\|"Speech Coding"]].

	*When entering the pulse positions  $N_{1}$  denotes the first triple of bits and  $N_{2}$  the second.		*When entering the pulse positions  $N_{1}$  denotes the first triple of bits and  $N_{2}$  the second.

Noah at 19:52, 21 January 2023

2023-01-21T19:52:49Z

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	}}		}}

	[[File:En_Bei_A_3_6.png\|right\|frame\|Tracks of the AMR~~–~~codec]]		[[File:En_Bei_A_3_6.png\|right\|frame\|Tracks of the AMR codec]]
	In the late 1990s, a very flexible, adaptive speech codec was developed and standardised in the form of the AMR codec. This provides a total of eight different modes with data rates between  $4.75 \ \rm kbit/s$  and  $12.2 \ \rm kbit/s$ .		In the late 1990s, a very flexible, adaptive speech codec was developed and standardised in the form of the AMR codec. This provides a total of eight different modes with data rates between  $4.75 \ \rm kbit/s$  and  $12.2 \ \rm kbit/s$ .