Echo Cancellation Support - Sierra Wireless MC5725 Hardware Integration Manual

CDMA and GSM / UMTS Mini Card Hardware Integration Guide
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In the event of a discrepancy in values between this guide and the Product Specification Document (PSD), the PSD takes precedence.
For Handset and Headset mode, the threshold of pain (+120
dBSPL) must not be exceeded at the maximum volume setting.
A good target for the medium volume setting is +94 dBSPL, as
this is a typical level for conversational speech.
Most audio gain should be added to the host audio front end
(within the PDA style codec gain blocks or amplifiers between
the host codec and transducers). Refer to the appropriate Mini
Card Product Specification Document for reference levels on
the modem receive and transmit side.

Echo cancellation support

The Mini Card offers four modes of echo cancellation to
support unique end‐unit audio capabilities (echo cancellation
can also be turned off completely). All echo cancellation is
near‐end (mobile TX) cancellation only. The network provides
some level of far‐end echo cancellation.
Table 4-3: Echo cancellation details
Mode
Handset
•
•
•
Headset •
•
•
Car kit
•
•
•
Proprietary and Confidential
Details
Short echo path (<16 ms travel time from speaker to
microphone)
Handset design requires good isolation between
speaker and microphone
Echo canceller allows full-duplex conversation with
absolute minimum echo
Short echo path (<16 ms travel time from speaker to
microphone)
Headset design may allow higher echo than
handset mode—microphone and speaker are physi-
cally closer
More aggressive echo canceller algorithm allows
full-duplex conversation on headsets with good
isolation
Long echo path (<64 ms travel time from speaker to
microphone)
Loud echo
For use with hands-free car kit or speakerphone
applications with mild distortion
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