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CDB6403 Datasheet(PDF) 10 Page - Cirrus Logic |
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CDB6403 Datasheet(HTML) 10 Page - Cirrus Logic |
10 / 54 page The Central Processing Unit (CPU) does all the other miscellaneous processing, like update con- trol and double talk detection. This processing has a critical influence on overall echo-cancella- tion performance. Double-talk detection is a particularly important part of this processing. Double-talk detection and other algorithms were carefully developed and validated at Crystal un- der real-world conditions. To increase the CS6403’s echo return-loss en- h an cement (ERLE), supplemental echo suppression is used. A sophisticated voice-detec- tion algorithm is used to reduce echo with minimal impact on conversation quality, assuring the highest quality conversation. Figure 3 describes the functional behavior of the CS6403 in a typical application. Digital data from the far-end interface comes into SDI of the CS6403 where it is acted upon by the various algorithms running in the CPU. First, a High- Pass Filter eliminates DC offset and low frequency noise before sending the far-end input data onto the summing node for the network echo canceller. Assuming there is no speech from the near-end, the signal after the summing node is unaffected. The signal then passes on to the AGC/Volume Control block where the signal level is boosted, if necessary. The volume control is implemented in part by the AGC (for more details, see the section entitled "Embedded Signal Processing Functions"). The signal then passes on to the Non-linear Echo Control block which controls the half-duplex failsafe and the supplementary echo suppressor which act to enhance and supplement the per- formance of the echo canceller. The signal after this block is then fed to both the speaker output and the input to the acoustic echo canceller (implemented by the AFP). The speaker output couples to the microphone input by various echo paths. The signal received at the microphone is then filtered and sent on to the summing node of the Acoustic Echo Canceller. The Acoustic Echo Canceller constructs a model of the echo paths between the speaker and mi- crophone and processes its input signal with its digital representation of the echo paths. As such, its output should very closely match the input from the microphone and so the output from the summing node should be a very small signal, which is referred to as the "error signal." This error signal is fed back to the echo canceller to let it adapt its performance should there be a change in the echo path. The Non-linear Echo Control block following the summing node further attenuates any vestiges of signal received at the microphone that origi- nated from the speaker. This signal is then sent to the far-end output by SDO as well as to the input of the Network Echo Canceller, where a function similar to that performed by the Acous- tic Echo Canceller is performed. - - + + SDI SDO SPKROUT CS6403 MICIN Near-End Output Near-End Input Far-End Input Far-End Output DSP or PCM Codec * * Optional * Non-linear Echo Control High Pass Filter High Pass Filter Network Echo Canceller Acoustic Echo Canceller AGC/ Volume Control Non-linear Echo Control Figure 3. Functional Diagram CS6403 10 DS192PP6 |
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