BCM4354 Data Sheet
Bluetooth Power Management Unit
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
Packet Loss Causes Ramp-down
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.
Broadcom®
October 15, 2014 • 4354-DS109-R
Page 40
BROADCOM CONFIDENTIAL
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