Sierra Wireless MC8775 Reference Manual page 88

MC87xx Extended AT Command Reference
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The embedded module can serve as an integral component of a
more complex audio system, such as a PDA with a separate
codec interfacing with the main processor. In this case, the
interface between the modem and PDA codec can be as simple
as line‐level audio with no transducer considerations. Phone‐
oriented functions such as echo cancellation and FIR filtering
are typically left to the module, while path‐switching and
transducer interfaces are the responsibility of the PDA codec.
Functions such as adjustable gain and volume settings, DTMF
and ringer tone generation, and mixing can be accomplished in
either codec, depending on the architecture of the particular
product. The interface between the module and host audio
systems is usually the primary audio interface set to line‐level
amplitudes, routed as differential pairs for noise immunity.
Figure 7-1: Audio block diagram
Audio profiles
The AT command set allows you to have different audio
configurations for different purposes. As an example, assume
you are embedding the module in a device that has a handset
mode and a speakerphone mode. Assume also that you want
to use different transmit gain, noise suppression, and echo
cancellation settings in each mode. You can store the settings
for each mode in separate audio profiles, then activate the
appropriate profile as your application switches to handset or
speakerphone mode.
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