3a. Speech Coders
-
Upload
erpsolanki -
Category
Technology
-
view
1.873 -
download
2
description
Transcript of 3a. Speech Coders
SPEECH CODECS
WLLMICRO-CELLULAR WILL
MACRO-CELLULAR WILL
32 kb/s
13.6 kb/s
DECT
GSM , CDMA, D-AMPS
BIT RATES
AUDIBLE RANGE
TELEPHONIC
PCM
VSAT
WLL
MOBILE
64 kb/s
20 Hz TO 20000Hz
300Hz to 3400Hz
16kb/s , 14.4kb/s , 9.6kb/s , 2.4 kb/s
32 kb/s , 13.6 kb/s
13.6 kb/s
REDUCING THE BIT RATE
WHY?
WHY TO REDUCE THE BIT RATE ?
TO ACCOMMODATE MORE INDIVIDUAL SPEECH CHANNELS WITHIN THE SAME TRANSMISSION CHANNEL (MEDIA BW )
THE COST TO BE PAID ?
SYSTEM CAPACITY
COST
REVENUE
LIMITED (TRANSMISSION) CHANNEL BW
HOW COME IS IT POSSIBLE?
IT IS POSSIBLE TO REDUCE THE BW WITHOUT MUCH COMPROMISE ON QUALITY
PROPERTIES OF HUMAN SPEECH &
EAR
•REDUNDANCIES IN THE SPEECH SIGNALS
•INTERMITTENT NATURE OF SPEECH
•PERCEPTUAL LIMITS OF HUMAN EAR
SPEECH REDUNDANCIES
•SPEECH ENERGY IS CONCENTRATED AT THE LOWER FREQUENCIES
•SPEECH SPECTRUM CHANGES RELATIVELY SLOWLY
(AS THE VIBRATION RATE OF THE VOCAL CORDS ALSO CHANGES RELATIVELY SLOWLY)
• SPEECH SOUNDS CAN BE MODELLED (AS PERIODIC & NOISY EXCITATIONS PASSING THROUGH THE VOCAL TRACT / FILTER)
INTERMITTENT NATURE OF SPEECH
SPEECH TRANSMISSION CHANNEL LIES INACTIVE
(3) END PARTY DELAYS 25%
FACTORS CONTRIBUTING INACTIVENESS
(1) TALK / LISTEN NATURE OF A NORMAL TWO WAY TELEPHONIC CONVERSATION
TRANSMISSION IN ONE DIRECTION IS FOR
< 50%(2) PAUSES 33%
SPEECH SPURTS 1.5 seconds
TLAF
AVERAGE FRACTION OF THE TOTAL CONNECT TIME DROPS TO AS LOW AS 25 % = Telephone Load Activity Factor
=TLAF > 0.25 ITU
THE CICUIT UTILISATION CAN BE IMPROVED BY DEMAND ASSIGNMENT OF THE CHANNEL
EAR
•STRONGER SENSITIVITY TO A SMALLER PORTION OF THE AUDIBLE FREQUENCY SPECTRUM
•LESS SENSITIVITY TO THE PHASE OF THE SIGNAL
THE DEVICE
WHAT IS THE DEVICE…..?
SPEECH CODECS
CLASSIFICATION / CATEGORIES
WAVEFORM CODECS
PCM
DPCM
ADPCM
VOCODERSLPC
HYBRID CELP
CODE EXCITED LINEAR PREDICTIVE
PERFORMANCE
PARAMETERS
• COMPLEXITY MOPS
• DELAY 30 m sec
• BIT RATE
• QUALITY
• COST
BIT RATE
DGREE OF COMPRESSION
8 BIT PCM 64 kb/s
11 BIT PCM 88 kb/s
ADPCM 32 kb/s
LPC < 4.8 kb/s
SPEECH - QUALITY
OBJECTIVE MEASURES
SUBJECTIVE MEASURES
SNR
HARMONIC DISTORTION
BW
M.O.S
MEAN OPINION SCORE
OBJECTIVE MEASURES4 QUALITY CLASSES
BROADCAST
TOLL
COMMUNICATION
SYNTHATIC
>7 kHz >30
3.1 kHz >30
2-3
2-3
HIGH QUALITY RADIO/TV
PSTN
POORER BUT STILL INTELLIGIBLE
WLL , MOBILE, MILITARY
BW SNR
HD %
< 2 kb/sRECOGNIZABILITY LOST MACHINELIKEROBOTICS
SUBJECTIVE MEASURES
M.O.S. QUALITY LISTENING EFFORTS
5 EXCELLENT NO EFFORT REQUIRED
4 GOOD ATTENTION NECESSARY BUT NO APPRICIABLE EFFORT REQUAD
3 FAIR MODERATE EFFORT REQUAD
2 POOR CONSIDERABLE EFFORT REQUAD
1 BAD NO MEANING UNDERSTOODWITH REASONABLE EFFORTS
M.O.S.
• 11 BIT PCM 4.9
• 08 BIT PCM (64 kb/s) 4.3
• ERROR FREE SPEECH
ADPCM (32 kb/s) 4.1
• MINIMUM 3.5
PARAMTERS
AT A GIVEN BIT RATE , SPEECH
QUALITY CAN BE IMPROVED BY
------------- THE COMPLEXITY OF
THE ALGORITHM & -------------THE
DELAY.
INCREASE IN
INCREASING
CLASSIFICATION / CATEGORIES
WAVEFORM CODECS
• SOURCE INDEPENDENT
• SUPERIOR SPEECH QUALITY
• HR BIT RATES
VOCODERS•SOURCE CODER
•VERY HIGH ECONOMY IN BIT RATE
•COMPLEX
VOCODERS
CODER
DECODER
SPEECHDIGITIZED (CODED SPEECH) SIGNALS
CODED SPEECH
SPEECH
OUTPUT
CODER
ADC
ADC
ADC
SPECTRUM ANALIZER
EXCITATION ANALIZER
M
U
X
SPEECH
VOCAL TRACT RESPONSE(FILTER)
VOICE DECISION
PITCH
DIGITIZED SPEECH
DECODER
NOISE SOURCE FILTER
SPEECH O/P
SYNTHESIZED
PITCH GENDEMUX
PITCH
VOICING DECISION
FILTER SHAPING DATA
CODED SPEECH I/P
EXAMPLES
BIT COMPLEXITY DELAY QUALITY M.O.S. RATE
kb/s MOPS ms
PCM 64 0.01 0 TOLL (High) 4.3
ADPCM 32 0.1 0 TOLL (High) 4.1
LPC 2.4 1.0 35 SYNTHETIC 2.5
MULTI PULSE 8.0 10 35 COMMUN 3.7 LPC
EXAMPLES
RELP VSAT 16kb/s RESIDUAL EXCITED
LINEAR PREDICTIVE
RPE-LTP GSM 13.6 kb/s REGULAR PULSE EXCITED LONG
TERM PREDICTIVE
TUTORIAL(1) WILL - IS IT A FACILITY TO THE SUBSCRIBER JUST LIKE CELLPHONE?
OR A TOOL FOR THE OPERATORS?
(2)DIFFERENCE BETWEEN WLL & WILL IS--
(3)GIVE THREE MAJOR DIFFERENCES BETWEEN MICRO & MACRO CELL WILL
(4) GIVE THREE EXAMPLES OF EACH
TUTORIAL(5) WHAT DO YOU MEAN BY “CELL” IN WILL?
(6) WHY CELLS ARE REQUIRED IN A WILL SYSTEM ?
(7) ON WHAT FACTORS DOES THE CELL SIZE DEPEND?
HOW TO DOUBLE THE CELL SIZE?
(8) WHY TO FURTHER DIVIDE THE CELL INTO SECTORS ?
TUTORIAL
(9) CALCULATE
HOW MANY SUBSCRIBERS CAN BE SERVED BY ONE BS/CELL ASSUMING FOLLOWING DATA
SIX SECTORS PER CELL WITH 10 RF 1.25 MHz BW CHANNELS IN EACH SECTOR
0.1 Erlg TRAFFIC PER SUBSCRIBER & 20 TO 40 ACTIVE LINES PER RF CHANNEL
TUTORIAL
(10) DRAW FUNTIONAL SCHEMATIC BLOCK DIGRAM OF
-DECT SYSTEM ARCHITECTURE
-CDMA ”””””””””””””””””
(11) IN DECT HOW DIFFERENT TONES (eg dial tone , NU tone) ARE SENT FROM CBS TO SE
TUTORIAL
(12) WHAT IS THE BANDWIDTH / BIT RATE (kbps) PER SUBSCRIBER IN CDMA AND DECT and HOW IS IT ACHIEVED ?
(13)WHAT ROLE THE SPEECH CODECS PLAY IN INCREASING THE SYSTEM CAPACITY
IN A WLL SYSTEM?
(14) SPEECH CODECS CAN BE CLASSIFIED AS ------
TUTORIAL
(15) DIFFERENTIATE BETWEEN 1G AND 2G SYSTEMS OF MOBILE SERVICES .
(16) HOW MANY BS AND SUBSCRIBERS CAN BE SERVED BY ONE DIU ?
TUTORIALFILL IN THE BLANKS
(1).MAXIMUM TRAFFIC HANDLED BY ONE CBS (DECT) IS --- AT 1%BLOCKING AND THUS 1 CBS CAN SERVE --------SUBSCRIBERS IF 0.05 Erlg / SUBS. THE INFORMATION RATE IS ------kbps ie THE RATE OF ------SPEECH CODEC
TUTORIAL(2) DECT WLL TENDER COVERS ----CITIES WITH ----LINES IN TOTAL -----SUPPLIED BY --------------(HFCL/SHYAM/LG/LUCENT) & -----------BY ------------------(HFCL/SHYAM/LG/LUCENT).
TUTORIAL
(3) IN VPT ------(CDMA/DECT) BASED WLL IS BEING INSTALLED WHICH IS OF ------(HFCL/SHYAM/LG/LUCENT) MAKE WITH ----(0/25/75/100 %)MOBILE AND ----(0/25/75/100 %)FIXED LINES ----------(68000 / 5 LAKH)LINES IN ALL
TUTORIAL
(4) FWT (LG’S CDMA FOR VPT) HAS ------------(INBUILT / SEPARATE) BATTERY WITH-----(2 / 20 HOURS) TALK TIME--------(10/20 HOURS) CHARGE TIME USES -------(SOLAR / MAINS / EITHER) CHARGING .
(5)THE DIFFERENCE BETWEEN WLL AND WILL IS THAT
TUTORIAL
(1)Vocoder with lower bit rate & the same Quality speech will be MORE / LESS Complex , MORE /LESS expensive (cost) , will add LESS/ MORE Delay(2)M.O.S. should not be less than------------
TUTORIAL
TRUE / FALSE
(1)IN CDMA THE CELL SIZE CAN BE INCREASE TO ANY LEVEL JUST BY INCREASING THE BS POWER
(2)GSM , CDMA & DAMS ARE EUROPIAN STANDARDS WHEREAS DECT , CT-2 & PHS ARE AMERICAN STANDARDS.
TUTORIAL
TRUE / FALSE
(3)GSM & DECT USE FDD WHEREAS DAMPS & CDMA USE TDD.
(4)DAMPS IS CALLED DUAL MODE BECAUSE IT CAN WORK BOTH AS A MICRO-CELLULAR AS WELL AS A MACRO-CELLULAR WLL.