CS4525 datasheet(33/91 Pages) CIRRUS

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DS726A1

CS4525

6.1.4.6

Parametric EQ

The CS4525 implements 5 fully programmable parametric EQ filters. Three of the filters are 2-channel

filters dedicated to the channel A/B pair, and the remaining two are single-channel filters dedicated to the

LFE channel generated by the bass manager.

The filters are implemented in the bi-quad form shown below.

This architecture is represented by the equation shown below where y[n] represents the output sample

value and x[n] represents the input sample value.

y[n] = b0x[n] + b1x[n-1] + b2x[n-2] - a1x[n-1] - a2x[n-2]

Equation 1. Bi-Quad Filter Equation

The coefficients are represented in binary form by 24-bit signed values stored in 3.21 two’s complement

format. The 3 MSB’s represent the sign bit and the whole-number portion of the decimal coefficient, and

the 21 LSB’s represent the fractional portion of the decimal coefficient. The coefficient values must be in

the range of -3.99996 decimal (80 00 00 hex) to 3.99996 decimal (7F FF FF hex).

The binary coefficient values are stored in registers 0Ah - 54h. Each 24-bit coefficient is split into 3 bytes,

each of which is mapped to an individually accessible register location. See the “Register Quick Refer-

ence” section beginning on page 61 for the specific register locations for each coefficient.

By default, all b0 coefficients are set to 1 decimal, and all other coefficients are set to 0 decimal. This im-

plements a pass-through function.

Parametric equalizers 1, 2, and 3 can be independently enabled and disabled for channel A and B with

the EnChAPEq and EnChBPEq bits located in the EQ Config register. The EnLFEPEq bit in the same reg-

ister enables and disables parametric equalizers 4 and 5 for the LFE channel.

Referenced Control

EnChAPEq .......................... “Enable Channel A Parametric EQ (EnChAPEq)” on page 74

EnChBPEq .......................... “Enable Channel B Parametric EQ (EnChBPEq)” on page 74

EnLFEPEq .......................... “Enable LFE Parametric EQ (EnLFEPEq)” on page 74

-a1

-a2

-1

x[n]

y[n]

Figure 16. Bi-Quad Filter Architecture

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