CSR8635 View Datasheet(PDF) - CSR plc
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CSR8635 Datasheet PDF : 105 Pages
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16.2.2 Noise Suppression with Wind Noise Reduction
The signal-channel noise suppression block is implemented in both signal paths. They are completely independent and
individually tuned. Noise suppression is a sub-band stationary / quasi-stationary noise suppression algorithm that uses
the temporal characteristics of speech and noise to remove the noise from the composite signal while maximising
speech quality. The current implementation can improve the SNR by up to 20dB.
In the transmit path, noise suppression aggressiveness is typically 95% improving SNR by 15 to 19dB to compensate
for the upstream processing and to maintain superior voice quality, while the Rx is typically tuned down to 80% improving
SNR by 8 to 12dB because of the cellular network processing. The user can parametrically adjust these default settings.
The noise suppression block contains a new WNR feature (send path only). The WNR removes unwanted noise during
a hands-free conversation, cleaning the audio for the far-end listener. It detects and tackle winds of various intensities
and durations. Once the wind is detected, a good balance between voice quality and WNR is achieved.
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â– Reduce amplitude variance observed from different users, phones and networks
Maintaining a consistent long-term loudness for the speech ensures it is more easily heard by the listener and it also
provides the subsequent processing block a larger amplitude signal to process. The behaviour of the AGC differs from
a dynamic range audio compressor. The convergence time for the AGC is much slower to reduce the non-linear
distortion.
16.2.8 Packet Loss Concealment
Bit errors and packet loss can occur in the Bluetooth transmission due to a variety of reasons, e.g. Wi-Fi interference
or RF signal degradation due to distance or physical objects. As a result of these errors, the user hears glitches referred
to as pops and clicks in the audio stream. The PLC block improves the receive path audio quality in the presence of
bit and packet errors within the Bluetooth link by using a variety of techniques such as pitch-based waveform
substitution.
Production Information
© Cambridge Silicon Radio Limited 2013
Confidential Information - This Material is Subject to CSR's Non-disclosure Agreement
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