TAS3103DBT datasheet(95/146 Pages) TI

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3.7.3

DRC Compression/Expansion Implementation Examples

The following four examples illustrate the steps that must be taken to calculate the DRC compression/expansion

coefficients for a specified DRC transfer function. The first example is an expansion/compression/expansion

implementation without discontinuities in the transfer function and represents a typical application. This first example

also illustrates one of the three modes of DRC saturation—32-bit dynamic range limitation saturation. The second

example is a compression/expansion/compression implementation. There is no discontinuity at T1 and 32-bit

dynamic range saturation occurs at low volume levels into the DRC. Example 2 also illustrates another form of DRC

saturation—maximum gain saturation. Example 3 illustrates the concept of infinite compression. Also, in Example 3,

32-bit dynamic range saturation occurs at low volume levels and the third form of DRC saturation is

illustrated—minimum gain saturation. Example 4 illustrates the ability of the DRC to realize a negative slope transfer

function. This example also illustrates two of the three forms of saturation—32-bit dynamic range saturation at low

volume levels and minimum gain saturation.

CAUTION:

The examples presented all exhibit some form of DRC saturation. This is not intended

to imply that all (or most) DRC transfer implementation exhibit some form of saturation.

Most practical implementations do not exhibit saturation. The examples are chosen to

explain by example the three types of saturation that can be encountered. But the

phenomenon of saturation can also be used to advantage in that it effectively provides

a means to implement more than three zones or regions of operation. If saturation is

intended, the regions exhibiting the transfer characteristic set by k0, k1, and k2 provide

three regions and the regions exhibiting saturation provide the additional regions of

operation.

3.7.3.1 Example 1—Expansion/Compression/Expansion Transfer Function With 32-Bit

Dynamic Range Saturation

For this example, the following transfer characteristics are chosen.

•

Threshold point 2: T2 = −26 dB, O2 = 30 dB

•

Threshold point 1: T1 = −101 dB, O1 = −7.5 dB

•

Region 0 slope: k0 = 0.05

≥ 1:1.05 Expansion

•

Region 1 slope: k1 = −0.5

≥ 2:1 Compression

•

Region 2 slope: k2 = 0.1

≥ 1:1.1 Expansion

The thresholds T1 and T2 are typically referenced, by the user, to the 0-dB signal level into the TAS3103. But to

determine the equivalent threshold point at the DRC input, it is necessary to take into account the processing gain

(or loss) between the TAS3103 SAP input and the DRC. Assume, as an example, the processing gain structure shown

in Figure 3−22. Inputting the data below the 8-bit headroom in the 48-bit DAP word and then routing only the upper

32 bits of the 48-bit word into the DRC, results in a 48-dB (8 bits x 6 dB/bit = 48 dB) attenuation of the signal level

into the DRC. Channel processing gain and use of the dedicated mixer into the DRC can revise this apparent 48-dB

attenuation in signal level into the DRC. In Figure 3−22, the 24 mixer gain into the DRC, coupled with a net channel

gain of 0 dB, changes the net 48-dB attenuation of the signal level into the DRC to a net attenuation of 24 dB.

For slopes:

Region 0 = 1:1.05 Expansion

≥ k0 = 1.05 − 1 = 0.05

= 00000.0000_1100_1100_1100_1100_110

= 0x0066666 in 5.23 format

Region 1 = 2:1 Compression

≥ k1 = 1/2 − 1 = -0.5

= 11111.1000_0000_0000_0000_0000_000

= 0xFC00000 in 5.23 format

Region 2 = 1:1.1 Expansion

≥ k2 = 1.1 − 1 = 0.1

= 00000.0001_1001_1001_1001_1001_100

= 0x00CCCCC in 5.23 format

TAS3103DBT Datasheet(PDF) 95 Page - Texas Instruments

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