TAS3004 datasheet(39/80 Pages) TI

39 / 80 page

5–1

5 Filter Processor

5.1

Biquad Block

The biquad block consists of seven digital biquad filters per channel organized in a cascade structure, as shown in

Figure 5–1. Each of these biquad filters has five downloadable 24-bit (4.20) coefficients. Each stereo channel has

independent coefficients.

Biquad 2 ...

Biquad 1

Biquad N

Figure 5–1. Biquad Cascade Configuration

5.1.1

Filter Coefficients

The filter coefficients for the TAS3004 device are downloaded through the I2C port and loaded into the biquad memory

space. Each biquad filter memory space has an independent address. Digital audio data coming into the device is

processed by the biquad block and then converted into analog waveforms by the DAC. Alternately, filters can be

loaded by asserting terminals on the GPI port.

5.1.2

Biquad Structure

The biquad structure that is used for the parametric equalization filters is as follows:

H(z)

0 )

z*1

) b

z*2

0 )

z*1

) a

z*2

NOTE: a0 is fixed at value 1 and is not downloadable.

The coefficients for these filters are represented in 4.20 format—4 bits for the integer part and 20 bits for the fractional

part. In order to transmit them over I2C, it is necessary to separate each coefficient into three bytes. The upper 4 bits

of byte 2 is the integer part, and the second nibble of byte 2, byte 1, and byte 0 are the fractional parts.

The filters can be designed using the automatic loudspeaker equalization program (ALE) or a script running under

MatLab named Filtermaker. Both of these tools are available from Texas Instruments.

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TAS3004 Datasheet(PDF) 39 Page - Texas Instruments