TAS3103 datasheet(105/146 Pages) TI

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3−45

Table 3−7. DRC Example 4 Parameters

DRC

PARAMETER

REQUIRED (SPECIFIED) VALUE

(NET GAINSAP Input-DRC = 0 dB)

I2C COEFFICIENT VALUE

−22 dBInput ≥ −70 dBDRC

−70/−6.0206= 11.626748

= 0x000005D0394825.23 Format

−102 dBInput ≥ −150 dBDRC

−150/−6.0206 = 24.91446

= 0x00000C750D0925.23 Format

100 dB

(100 + 24.0824)/6.0206 = 20.609640

= 0x00000A4E08B025.23 Format

0 dB

(0 + 24.0824)/6.0206

= 4.000000

= 0x00000200000025.23 Format

1:1.4 Expansion

1.4 − 1 = 0.4 = 0X03333335.23 Format

1:−1 Transfer

(1/−1) − 1 = −1 −1 = −2 = 0XF0000005.23 Format

1:1.5 Expansion

1.5 − 1 = 0.5 = 0x04000005.23 Format

3.8

Spectrum Analyzer/VU Meter

The TAS3103 contains an I2C bus programmable function block that can serve as either a spectrum analyzer or a

volume unit (VU) meter. Figure 3−26 shows the structure of this function block and lists the I2C subaddress of the

parameters that control it.

The block consists of 10 biquad filters, each followed by an rms estimator and a logarithmic converter. Two nodes

provide input to the block, with each node servicing five of the 10 biquad filters. Audio from input node s can either

come exclusively from channel 1, channel 2, channel 3, or from a gain-weighted combination of these channels. Audio

from input node t can also come exclusively from either channel 1, channel 2, or channel 3, or from a gain-weighted

combination of these channels. The spectrum analyzer then can be used to divide the audio frequency band into ten

frequency bins to examine the spectrum of the audio data stream on channel 1, channel 2, channel 3, or any

combination of these channels. The spectrum analyzer can also be used to divide the audio frequency band into five

frequency bins to examine the spectral content of two of the channels independently.

The VU meter is a special case of the spectrum analyzer that uses only the outputs from biquad 5 and biquad 6.

Typically, for the VU meter, one channel would be routed to biquad 5 (node s) and a different channel would be routed

to biquad 6 (node t). Each biquad filter would be assigned a band pass transfer function that encompasses most of

the audio band, or the filter could be configured as a pass-through device to see the full spectral band. The two outputs

then would be a measure of the energy on the two channels. Other options for the VU meter are also available. For

example, by properly setting the coefficients on biquad 5 and biquad 6, the concurrent measurement of bass and

treble volume levels on a single channel could be made.

Mixer and summation elements preceding the two input nodes s and t provide a means of adjusting the spectrum

analyzer and VU meter outputs relative to the incoming audio data stream. The spectrum analyzer and VU meter

outputs are unsigned 5.3 format base 2 logarithmic numbers. The integer part of the number designates the most

significant bit (in the 48-bit digital audio processor − DAP − word) occupied by the magnitude of the rms estimate of

the biquad filter output. A value of 31 means the magnitude of the rms estimate occupies bit 47 of the 48-bit DAP word

(bit 48 is the sign bit, and using the absolute value of the biquad filter output in determining the rms estimate makes

this bit always 0 in value). A value of 30 means the magnitude of the rms estimate occupies bit 46 and this pattern

continues with a value of 1 signifying the magnitude of the rms estimate occupies bit 17. A value of 0 signifies that

the magnitude of the rms estimate is below bit 17. The fractional digits in the 5.3 formatted number are simply the

three bits below the most significant data bit. If the rms estimate lies below bit 16 of the 48-bit DAP word, the spectrum

analyzer/VU meter output is 0.0. Figure 3−27 gives examples of logarithmic outputs for different 48-bit rms estimate

values.

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