1 voice quality enhancements 2 outline acoustic and network echo noise reduction (nr) mobile...
Post on 18-Dec-2015
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Voice Quality Enhancements
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Outline
• Acoustic and network echo
• Noise Reduction (NR)
• Mobile Cross-talk Control (MCC)
• Noise Level Compensation (NLC)
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Causes of echoReflection
Delay
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Echo in telecommunications systems
• Network (or PSTN, or electrical) echo– Generated by electrical reflection of the signal
• Acoustic echo– Generated by acoustic reflection of the audio signal
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Electrical (PSTN) Echo
4-wiretransmissionnetwork
Hybrid2-wiresubscriberline
PSTNsubscriber
Echo
PSTN: Public Switched Telephone Network
Mismatching in the impedance
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Acoustic Echo
Loudspeaker
Microphone
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Acoustic Echo Control - Terminals
• Terminals are different in terms of– Size
– Design
– Internal design of Acoustic Echo Cancellation
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Pure delay and End Path Delay
time
Echo Path Delay (EPD) G.168
Pure delay
Example of an impulse response of an echo path
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Different Echo type characteristics
PSTN echo (Electrical echo)
time
64 ms
time>5-10 ms
120-320 ms
MS echo(Acoustic echo)
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Echo tolerance
EchoReturnLoss(ERL)
dB
Echo ToleranceCurve
Tolerable
Intolerable
Delay (msec)
AnalogNetworks
DigitalNetworks Satellite
200 300
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Mobile Cross-talk Control (MCC)Acoustic Echo Control
Digitalcellularsubscriber
PSTNsubscriber
DigitalCellular System
Network echo
ECP
Mobileservices
SwitchingCenter
Acoustic echo
NetworkEcho Canceller
MobileCross-talk Control
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Noise Reduction (NR)Reduce the background noise on the mobile side
ECP: Echo Canceller in PoolPSTN: Public Switched Telephone Network
PSTNsubscriber
DigitalCellular System
Network echo
MobileSwitching
CenterDigitalcellularsubscriber
Mobile side
ECP
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Noise Reduction (NR)Reduce the background noise on the PSTN side
ECP: Echo Canceller in PoolPSTN: Public Switched Telephone Network
PSTNsubscriber
DigitalCellular System
Network echo
MobileSwitching
CenterDigitalcellularsubscriber
ECP
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Noise Level Compensation (NLC)Improves audibility in noisy environment
ECP
NLC