Transcript Commercial presentation - ISTI-CNR

Voice Quality Enhancements
1
Outline
• Acoustic and network echo
• Noise Reduction (NR)
• Mobile Cross-talk Control (MCC)
• Noise Level Compensation (NLC)
2
Causes of echo
Reflection
Delay
3
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
4
Electrical (PSTN) Echo
4-wire
transmission
network
2-wire
subscriber
line
Hybrid
PSTN
subscriber
Echo
Mismatching in the impedance
PSTN: Public Switched Telephone Network
5
Acoustic Echo
Microphone
Loudspeaker
6
Acoustic Echo Control - Terminals
• Terminals are different in terms of
– Size
– Design
– Internal design of Acoustic Echo Cancellation
7
Pure delay and End Path Delay
Echo Path Delay (EPD) G.168
Pure delay
time
Example of an impulse response of an echo path
8
Different Echo type characteristics
PSTN echo
(Electrical
echo)
time
64 ms
MS echo
(Acoustic
echo)
time
>5-10 ms
120-320 ms
9
Echo tolerance
Echo
Return dB
Loss
(ERL)
Tolerable
Echo Tolerance
Curve
Intolerable
Delay (msec)
200
Analog
Networks
Digital
Networks
300
Satellite
10
Mobile Cross-talk Control (MCC)
Acoustic Echo Control
Acoustic
echo
Network
echo
PSTN
subscriber
Mobile
services
Switching
Center
Digital
Cellular System
ECP
Network
Echo Canceller
Mobile
Cross-talk Control
11
Digital
cellular
subscriber
Noise Reduction (NR)
Reduce the background noise on the mobile side
Network
echo
Mobile
Switching
Center
Mobile side
Digital
cellular
subscriber
PSTN
subscriber
Digital
Cellular System
ECP
ECP: Echo Canceller in Pool
PSTN: Public Switched Telephone Network
12
Noise Reduction (NR)
Reduce the background noise on the PSTN side
Network
echo
Mobile
Switching
Center
Digital
cellular
subscriber
PSTN
subscriber
Digital
Cellular System
ECP
ECP: Echo Canceller in Pool
PSTN: Public Switched Telephone Network
13
Noise Level Compensation (NLC)
Improves audibility in noisy environment
NLC
ECP
14