TAS3103ADBT datasheet(109/154 Pages) TI2

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3−46

Table 3−7. DRC Example 4 Parameters

DRC

PARAMETER

REQUIRED (SPECIFIED) VALUE

(NET GAINSAP Input-DRC = 0 dB)

I2C COEFFICIENT VALUE

−22 dBInput

≥ −70 dB

DRC

−70/−6.0206 = 11.626748

= 0x0000 05D0 394825.23 format

−102 dBInput

≥ −150 dB

DRC

−150/−6.0206 = 24.91446

= 0x0000 0C75 0D0925.23 format

100 dB

(100 + 24.0824)/6.0206 = 20.609640

= 0x0000 0A4E 08B025.23 format

0 dB

(0 + 24.0824)/6.0206 = 4.000000

= 0x0000 0200 000025.23 format

1:1.4 expansion

1.4 − 1 = 0.4 = 0x0333 3335.23 format

1:−1 transfer

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

1:1.5 expansion

1.5 − 1 = 0.5 = 0x0400 0005.23 format

3.8

Spectrum Analyzer/VU Meter

The TAS3103A contains an I2C bus programmable function block that can serve as either a spectrum analyzer or

a volume unit (VU) meter. Figure 3−29 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 10

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.

TAS3103ADBT Datasheet(PDF) 109 Page - Texas Instruments

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