Cirrus Logic CS48LV13 - Manual (Page 8)

DS1057F1 8
3.3 Tx Voice DSP Chain
The CS48LV13 includes two additional processing groups:
5. Speech DSP Chain
6. Advanced Audio Playback DSP Chain
Cirrus Logic provides two specialized tools for controlling and tuning the various processing groups. For voice- and
speech-related processing groups, the RAPID2 tool provides real-time analysis and tuning of all parameters. For
audio-playback chains, a specialized version of the DSP Composer tool is used for real-time control and tuning.
Each group may operate in more than one mode. Typically, smartphones have three or more operating modes:
a) Handset mode using processing Groups 1, 2, and 3
b) Speakerphone mode using processing Groups 1, 2, and 3
c) Media playback mode using processing Group 4 or 6
d) ASR mode using process using Group 5
Each mode may have tuning variations; for example, handset mode may include default tuning (using integrated
microphones and receiver), pass-through tuning for BT accessories, which perform their own voice processing and wired
headset tuning.
Tablets may have a single mode, similar to Speakerphone Mode, or may have multiple modes using different microphones
and processing, depending on their orientation and desired use model, such as portrait, landscape, handheld, on stand,
personal or group. Similarly, other applications may have a single or multiple modes using one or more processing groups.
3.3 Tx Voice DSP Chain
The Tx Voice DSP Chain accepts raw PCM voice data from one or two microphones and uses this data, along with any
incorporated spatial information, to remove undesired noise and competing speech while preserving voice integrity. It also
includes AEC and residual echo suppression functions to remove echo. In combination with the Voice DSP Control and
Detection and Rx Voice DSP Chain groups, it manages full-duplex operation. A number of additional voice processing
blocks are included to provide a natural, intelligible, and consistent PCM voice stream.
Fig. 3-3 is a simplified diagram of the Tx Voice Chain. The start of the chain is fed by one or two voice PCM streams
originating from the voice microphones and arriving on one of the CS48LV12/13’s two I 2 S DAI inputs (typically DAI_2).
The output of the chain, Tx Out, is transmitted out of one of the two I 2 S DAO outputs (typically DAO_1), typically a host
processor, applications processor, or system on a chip (SoC), which then sends the stream to a digital baseband or other
network processor.
Figure 3-3. Tx Voice DSP Chain
3.4 Programmable Gain Amplifiers (PGAs)
One set of PGAs controls the level of the input streams from the mic and 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 can be used
to adjust PGA gain level to maintain maximum SNR without danger of clipping.
3.5 Noise Reduction
SoundClear Voice technology uses a variety of innovative techniques and algorithms to distinguish between desired
speech, undesired speech (competing talkers), and nonspeech, and then suppresses all but desired speech.
In a two-mic configuration, SoundClear Voice technology uses signature analysis techniques to distinguish and eliminate
noise and to preserve the vocal quality of speech. Also, a proprietary beam forming technology analyzes the aural space
around the user and classifies sounds, based on direction of arrival and proximity. It also makes real-time voice-tracking
PGA
Noise
Reduction
Acoustic Echo Canceller
Residual Echo Suppressor
NLP
Spectrally Matched
Comfort Noise
Dynamic
FlexEQ
ALC PGA