Echo is Your Enemy Echo Cancellation is Your Solution.
-
Upload
kierra-crow -
Category
Documents
-
view
223 -
download
0
Transcript of Echo is Your Enemy Echo Cancellation is Your Solution.
Agenda
What is Echo?
What Causes Echo?
Echo Characteristics
Echo and Speech Recognition:A Real-World Example
Brooktrout Solutions
What is Echo?
Outgoing Signals are Reflected Back to the Input– Delayed: transmission latency– Attenuated: hybrid, network echo cancellation– Distorted: varying electrical characteristics of path
Types of Echo– Acoustic echo
– Speakerphones, hands-free phones– Multiple acoustic reflections from surrounding surfaces
– Echo in wireless networks– Very large, variable propagation delays
– Echo in VoIP networks– Codec, jitter buffers introduce latency
– Hybrid (line) echo– An inherent problem in PSTN networks
Hybrid HybridPSTNNetwork
What Causes Echo?
2 – wire 2 – wire
– 2–wire connections between home and switch
4 – wire connections within PSTN network
– 4–wire connections within the digital network
Impedance mismatch causes reflections
ASR System
Echo cancellation required for ASR systems
Echo Cancellation
Echo Cancellation
Echo Characteristics
…what ci t y will you be fly ing to..?
Outgoing Prompt
IncomingEcho
5-50 msec delay 6 – 11 dB attenuation
Echo and ASR:A Real-World Example
A Simple Speech-Enabled Travel Application…
Typical prompt and resulting echo
The user “barges in”
What the ASR system hears and recognizes– With 16 msec echo cancellation– With 32 msec echo cancellation
A Typical Prompt…
“Welcome to Brooktrout Air…”– An introductory prompt calibrates the echo
cancellation algorithm before barge-in is enabled
“What city would you like to leave from?”
The response “Boston” is correctly recognized
But echo can interfere with recognition…
Echo Cancellation
Hybrid Hybrid
Echo Cancellation
PSTNNetwork
ASR System
Barge-In With Echo
The ASR system plays a prompt…
…the user barges in…
…but the prompt echo mixes with the user’s voice, impacting voice detection and recognition accuracy
Echo
“Austin” mixed with the echo of the prompt “…be…”is misrecognized as “Boston” Boston
Echo and ASR
ASR accuracy depends on effective echo cancellation– Typical system requires 16-20 msec echo cancellation– Many instances where 32 msec echo cancellation is
recommended
Options for 32 msec echo cancellation– Install a standalone echo cancellation system (expensive)– Use a telephony board with onboard 32 msec echo
cancellation (inexpensive)
16 msec EC
A system with excessive echo
and/or delay
32 msec EC
Compare the echo
Brooktrout ASR Solutions:Carriers and Service Providers
TR1000™ Carrier-Grade Telephony Board– PCI, cPCI form factors– Digital interfaces (T1/E1, ISDN)– Broad OS support
– Windows, Solaris, Linux, Unixware
Full-Featured Media Resource Platform– High-density ASR support
– Up to 96 channels per board, 192 per system– The highest channel density on the market today
– Vendor-independent APIs for ASR/TTS
– IP with on-board packetization– Enhanced V.34 fax– High density conferencing
With onboard 16 or 32 msec echo cancellation
Brooktrout ASR Solutions:Carriers and Service Providers
TR1000™ Carrier-Grade Telephony Board– PCI, cPCI form factors– Digital interfaces (T1/E1, ISDN)– Broad OS support
– Windows, Solaris, Linux, Unixware
Full-Featured Media Resource Platform– High-density ASR support
– Up to 96 channels per board, 192 per system– The highest channel density on the market today
– Vendor-independent APIs for ASR/TTS
– IP with on-board packetization– Enhanced V.34 fax– High density conferencing
With onboard 16 or 32 msec echo cancellation
Brooktrout ASR Solutions:Enterprise Applications
TR1100™ High-Density Telephony Board– Up to 60 channels per board– 8/16 msec echo cancellation– Digital interface (T1/E1)– PCI– Windows NT and 2000
Vantage™ Series– Ideal for small and medium
business applications– Up to 4 analog channels per board– 8/16 msec echo cancellation– ISA, PCI – Windows NT and 2000
Summary
Echo is Your Enemy– It’s everywhere within the PSTN network– It can destroy barge-in recognition accuracy
Echo Cancellation is Your Solution– Telephony boards can provide effective
onboard echo cancellation– How much is enough?
– 16 msec typical
– 32 msec otherwise
The new TR1000 delivers the best echo cancellationand highest channel density on the market today