BCM4354 datasheet(41/192 Pages) CYPRESS

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Bluetooth Power Management Unit

BCM4354 Data Sheet

BROADCOM CONFIDENTIAL

Broadcom®

October 15, 2014 • 4354-DS109-R

Page 40

Packet Loss Concealment

Packet Loss Concealment (PLC) improves apparent audio quality for systems with marginal link performance.

Bluetooth messages are sent in packets. When a packet is lost, it creates a gap in the received audio bit-stream.

Packet loss can be mitigated in several ways:

• Fill in zeros.

• Ramp down the output audio signal toward zero (this is the method used in current Bluetooth headsets).

• Repeat the last frame (or packet) of the received bit-stream and decode it as usual (frame repeat).

These techniques cause distortion and popping in the audio stream. The BCM4354 uses a proprietary waveform

extension algorithm to provide dramatic improvement in the audio quality. Figure 7 and Figure 8 show audio

waveforms with and without Packet Loss Concealment. Broadcom PLC/BEC algorithms also support wide band

speech.

Figure 7: CVSD Decoder Output Waveform Without PLC

Figure 8: CVSD Decoder Output Waveform After Applying PLC

Audio Rate-Matching Algorithms

The BCM4354 has an enhanced rate-matching algorithm that uses interpolation algorithms to reduce audio

stream jitter that may be present when the rate of audio data coming from the host is not the same as the

Bluetooth or FM audio data rates.

Packet Loss Causes Ramp-down

BCM4354 データシート(PDF) 41 Page - Cypress Semiconductor