CS47L85 datasheet(85/370 Pages) CIRRUS

85 / 370 page

CS47L85

Rev 4.3

GAIN LIMITS

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

DRCn_NG_MINGAIN. These limits can be used to alter the DRC response from that illustrated in Figure 29. If the range

between maximum and minimum gain is reduced, then 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 mimimum 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.

DYNAMIC CHARACTERISTICS

The dynamic behaviour 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 register fields are described in Table 14. Note that the register defaults are suitable for general purpose microphone

use.

ANTI-CLIP CONTROL

The DRC includes an Anti-Clip 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 Anti-Clip 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 Anti-Clip feature operates entirely in the digital domain. It cannot be used to prevent signal clipping in the

analogue domain nor in the source signal. Analogue clipping can only be prevented by reducing the analogue signal gain

or by adjusting the source signal.

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, then the normal decay rate

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

CS47L85 Datasheet(PDF) 85 Page - Cirrus Logic