WM1811A datasheet(80/328 Pages) WOLFSON

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WM1811A

Production Data

PD, November 2013, Rev 4.1

RETUNETM MOBILE PARAMETRIC EQUALIZER (EQ)

The ReTune

TM Mobile Parametric EQ is a circuit which can be enabled in the digital playback path of

the WM1811A audio interfaces. The function of the EQ is to adjust the frequency characteristic of the

output in order to compensate for unwanted frequency characteristics in the loudspeaker (or other

output transducer). It can also be used to tailor the response according to user preferences, for

example to accentuate or attenuate specific frequency bands to emulate different sound profiles or

environments e.g. concert hall, rock etc.

The WM1811A provides two stereo EQ circuits; these are associated with AIF1 and AIF2 respectively.

The EQ is enabled in these signal paths using the register bits described in Table 29.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R1152 (0480h)

AIF1 DAC1

EQ Gains (1)

AIF1DAC1_EQ_E

Enable EQ in AIF1DAC playback

path

0 = Disabled

1 = Enabled

R1408 (0580h)

AIF2 EQ Gains

(1)

AIF2DAC_EQ_EN

Enable EQ in AIF2DAC playback

path

0 = Disabled

1 = Enabled

Table 29 ReTune

TM Mobile Parametric EQ Enable

The following description of the EQ is applicable to both EQ circuits. The associated register control

fields are described in Table 31 and Table 32 for the respective EQs. The EQ provides selective

control of 5 frequency bands as described below.

The low frequency band (Band 1) filter can be configured either as a peak filter or a shelving filter.

When configured as a shelving filter, is provides adjustable gain below the Band 1 cut-off frequency.

As a peak filter, it provides adjustable gain within a defined frequency band that is centred on the

Band 1 frequency.

The mid frequency bands (Band 2, Band 3, Band 4) filters are peak filters, which provide adjustable

gain around the respective centre frequency.

The high frequency band (Band 5) filter is a shelving filter, which provides adjustable gain above the

Band 5 cut-off frequency.

The EQ can be configured to operate in two modes - “Default” mode or “ReTune

TM Mobile” mode.The

associated register control fields are described in Table 31 and Table 32 for the respective EQs.

DEFAULT MODE (5-BAND PARAMETRIC EQ)

In default mode, the cut-off/centre frequencies are fixed as per Table 30. The filter bandwidths are

also fixed in default mode. The gain of the individual bands (-12dB to +12dB) can be controlled as

described in Table 31.

The cut-off / centre frequencies noted in Table 30 are applicable to a sample rate of 48kHz. When

using other sample rates, these frequencies will be scaled in proportion to the selected sample rate for

the associated Audio Interface (AIF1 or AIF2).

If AIF1 and AIF2 are operating at different sample rates, then the cut-off / centre frequencies will be

different for the two interfaces. Note that the frequencies can be set to other values by using the

features described in “ReTune

TM Mobile Mode”.

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