WM8742GEDSSLASHV datasheet(38/66 Pages) CIRRUS

38 / 66 page

WM8742

Rev 4.4

NORMAL PCM MODE DIGITAL FILTER SELECTION

The WM8742 has a number of advanced digital filters that can be selected in all PCM operation

modes (with the exception of 8FS mode).

BIT

LABEL

DEFAULT

DESCRIPTION

Filter Control

06h

[2:0]

FIRSEL

000

Selects FIR1 filter response

000 = Response 1

001 = Response 2

010 = Response 3

011 = Response 4

100 = Response 5

Table 38 PCM Advanced Digital Filter Selection

Five digital filters are available for selection in each of the three OSR modes (low, medium and high

rate) as selected by the OSR bit described in Table 20. It is recommended that the device is muted

before the filter response is changed to prevent noise as the filters are reset from appearing on the

outputs. A summary of the filter characteristics is given in Table 39 below:

OSR

RESPONSE

NOTES

Low

Linear phase half-band filter for backward compatibility

Minimum phase ‘soft-knee’ filter

Minimum phase half-band filter

Linear phase apodising filter

Minimum phase apodising filter

Medium

Linear phase ‘soft-knee’ filter

Minimum phase ‘soft-knee’ filter

Linear phase ‘brickwall’ filter

Minimum phase apodising filter

Linear phase apodising filter

High

Linear phase ‘soft-knee’ filter

Minimum phase ‘soft-knee’ filter

Linear phase ‘brickwall’ filter

Minimum phase apodising filter

Linear phase apodising filter

Table 39 PCM Digital Filter Summary

For full details of the filter characteristics available in normal PCM mode, please see Table 64 to Table

66 and Figure 28 to Figure 57.

8FS MODE DIGITAL FILTER

In 8FS mode, the majority of the internal filters are bypassed. In this mode, the data is filtered using

only the filter characteristic described by Table 67 and shown in Figure 58 and Figure 59.

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