Cirrus Logic CS48LV13 - Manual (Page 10)

DS1057F1 10
3.9 Automatic Level Control (ALC)
3.9 Automatic Level Control (ALC)
Tx voice level can vary greatly based on talker loudness, product distance and orientation. By distinguishing between voice
and noise levels and adjusting Tx voice level accordingly, the ALC is able to maintain more consistent Tx voice loudness
without boosting noise in periods of silence. This improves far-end user experience and product performance when it is
held away from the mouth or off-axis.
3.10 Rx Voice DSP Chain
Figure 3-4. Rx Voice DSP Chain
Table 3-1 describes the functions in the Rx voice DSP chain.
3.11 Voice DSP Control and Detection Group
The voice DSP control and detection group encompasses several functions related to managing the combined Tx and Rx
Voice DSP Chains. Key functions include full-duplex communication state control, voice detection, noise classification,
AEC, and residual echo-suppression control.
3.12 Audio Playback DSP Chain/Advanced Audio Playback DSP Chain
This chain consists of various audio postprocessing modules for enhancement of media playback. The modules have
multiple use modes for support of both integrated speakers and plug-in headphones. Both the CS48LV12 and CS48LV13
integrate the following Cirrus Logic algorithms:
• Virtual surround
• Bass enhancement
• Bass virtualization
• Parametric EQ
• Multiband compressor
A special version of Cirrus Logic® DSP Composer tool enables selection of the desired combination of algorithms and
their tuning.
Optionally, the CS48LV13 supports popular postprocessing algorithms from Dolby and DTS. A license agreement with
Dolby or DTS is required to use this feature. DSP composer support for these algorithms is also available.
Table 3-1. Rx Voice DSP Chain Descriptions
Function Description
Programmable gain
amplifiers (PGAs) One set of PGAs controls the level of the input streams from the host downlink (Rx). Another PGA at the output of
the chain controls the level of the output stream (Tx Out). The RAPID2 tool includes PGA level meters with clipping
detectors that can be used to adjust PGA gain level to maintain maximum SNR without danger of clipping.
Noise reduction Similar function as Noise Reduction in Tx Voice Chain, but operating on more limited information, because the Rx
stream from the far-end uses a single channel and lacks the spatial information necessary to perform the high levels
of SNRI achieved by the multi-mic algorithms applied to the Tx stream. However, the Rx noise-reduction function
can significantly suppress far-end noise, especially stationary-type noises.
Dynamic (PEQ) This block is the same for both the Tx and Rx Voice DSP chains. See Section 3.8 .
Automatic level control
(ALC) Rx voice level can vary greatly, based on the far-end talkers loudness and on the phone’s orientation. By
distinguishing between voice and noise levels and by adjusting Rx voice level accordingly, the ALC can maintain
more consistent Rx voice volume, without boosting noise during silent periods. This improves near-end user
experience and product performance when a far-end talker speaks softly or holds the phone away from their mouth.
Automatic volume control
(ALC) As ambient noise level rises, it can be more difficult for the user to understand the caller, regardless of whether the
product is being used in handset or hands-free/speakerphone mode. The ALC block automatically adjusts receive
loudness, based on ambient noise level.
Comfort noise generator
(CNG) CNG is used to inject levels of synthesized noise into the Rx stream during periods of silence, so that the near-end
user avoids hearing noise modulation.
PGA
Comfort
Noise
Automatic Volume
Control
Automatic Level
Control
Dynamic
FlexEQ
Noise
Reduction
PGA