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Voice Quality Enhancements

Voice Quality Enhancements. Outline. Acoustic and network echo Noise Reduction (NR) Mobile Cross-talk Control (MCC) Noise Level Compensation (NLC). Reflection. Delay. Causes of echo. Echo in telecommunications systems. Network (or PSTN, or electrical) echo

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Voice Quality Enhancements

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  1. Voice Quality Enhancements

  2. Outline • Acoustic and network echo • Noise Reduction (NR) • Mobile Cross-talk Control (MCC) • Noise Level Compensation (NLC)

  3. Reflection Delay Causes of echo

  4. 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

  5. Electrical (PSTN) Echo 4-wire transmission network 2-wire subscriber line Hybrid PSTN subscriber Echo Mismatching in the impedance PSTN: Public Switched Telephone Network

  6. Microphone Acoustic Echo Loudspeaker

  7. Acoustic Echo Control - Terminals • Terminals are different in terms of • Size • Design • Internal design of Acoustic Echo Cancellation

  8. Pure delay and End Path Delay Echo Path Delay (EPD) G.168 Pure delay time Example of an impulse response of an echo path

  9. Different Echo type characteristics PSTN echo (Electrical echo) time 64 ms MS echo (Acoustic echo) time >5-10 ms 120-320 ms

  10. Echo tolerance Echo Return Loss (ERL) dB Tolerable Echo Tolerance Curve Intolerable Delay (msec) 200 300 Analog Networks Digital Networks Satellite

  11. Mobile Cross-talk Control (MCC)Acoustic Echo Control Acoustic echo Mobileservices Switching Center Network echo Digital cellular subscriber PSTN subscriber Digital Cellular System ECP Network Echo Canceller Mobile Cross-talk Control

  12. Noise Reduction (NR)Reduce the background noise on the mobile side Mobile 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 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

  14. Noise Level Compensation (NLC)Improves audibility in noisy environment NLC ECP

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