CS47L35 datasheet(54/300 Pages) CIRRUS

54 / 300 page

DS1085F3

CS47L35

4.3 Digital Core

Parameter Y0, the output level for a 0 dB input, is not specified directly but can be calculated from the other parameters

using Eq. 4-1.

Equation 4-1. DRC Compression Calculation

4.3.5.2 Gain Limits

The minimum and maximum gain applied by the DRC is set by DRCn_MINGAIN, DRCn_MAXGAIN, and DRCn_NG_

MINGAIN. These limits can be used to alter the DRC response from that shown in Fig. 4-18. If the range between

maximum and minimum gain is reduced, the extent of the dynamic range control is reduced.

The minimum gain in the compression regions of the DRC response is set by DRCn_MINGAIN. The minimum gain in the

noise-gate region is set by DRCn_NG_MINGAIN. The minimum gain limit prevents excessive attenuation of the signal

path.

The maximum gain limit set by DRCn_MAXGAIN prevents quiet signals (or silence) from being excessively amplified.

4.3.5.3 Dynamic Characteristics

The dynamic behavior determines how quickly the DRC responds to changing signal levels. Note that the DRC responds

to the average (RMS) signal amplitude over a period of time.

The DRCn_ATK determines how quickly the DRC gain decreases when the signal amplitude is high. The DRCn_DCY

determines how quickly the DRC gain increases when the signal amplitude is low.

These fields are described in Table 4-13. The register defaults are suitable for general-purpose microphone use.

4.3.5.4 Anticlip Control

The DRC includes an anticlip feature to avoid signal clipping when the input amplitude rises very quickly. This feature uses

a feed-forward technique for early detection of a rising signal level. Signal clipping is avoided by dynamically increasing

the gain attack rate when required. The anticlip feature is enabled using the DRCn_ANTICLIP bit.

Note that the feed-forward processing increases the latency in the input signal path.

Note that the anticlip feature operates entirely in the digital domain. It cannot be used to prevent signal clipping in the

analog domain nor in the source signal. Analog clipping can only be prevented by reducing the analog signal gain or by

adjusting the source signal.

4.3.5.5 Quick Release Control

The DRC includes a quick-release feature to handle short transient peaks that are not related to the intended source

signal. For example, in handheld microphone recording, transient signal peaks sometimes occur due to user handling, key

presses or accidental tapping against the microphone. The quick-release feature ensures that these transients do not

cause the intended signal to be masked by the longer time constant of DRCn_DCY.

The quick-release feature is enabled by setting the DRCn_QR bit. When this bit is enabled, the DRC measures the crest

factor (peak to RMS ratio) of the input signal. A high crest factor is indicative of a transient peak that may not be related

to the intended source signal. If the crest factor exceeds the level set by DRCn_QR_THR, the normal decay rate (DRCn_

DCY) is ignored and a faster decay rate (DRCn_QR_DCY) is used instead.

4.3.5.6 Signal Activity Detect

The DRC incorporates a configurable signal-detect function, allowing the signal level at the DRC input to be monitored

and to be used to trigger other events. This can be used to detect the presence of a microphone signal on an ADC or DMIC

channel, or can be used to detect an audio signal received over the digital audio interface.

DRCn_KNEE_OP

DRCn_KNEE_IP

DRCn_HI_COMP

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