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DRC Input Level

1:1 Transfer Function

Implemented Transfer Function

Region

M0014-01

TAS5548

www.ti.com

SLES270 – NOVEMBER 2012

Figure 3-16 illustrates a typical DRC transfer function.

Figure 3-16. Dynamic Range Compression (DRC) Transfer Function Structure

The three regions shown in Figure 3-16 are defined by three sets of programmable coefficients:

•

Thresholds T1 and T2 define region boundaries.

•

Offsets O1 and O2 define the DRC gain coefficient settings at thresholds T1 and T2, respectively.

•

Slopes k0, k1, and k2 define whether compression or expansion is to be performed within a given

region. The magnitudes of the slopes define the degree of compression or expansion to be performed.

The three sets of parameters are all defined in logarithmic space and adhere to the following rules:

•

The maximum input sample into the DRC is referenced at 0 dB. All values below this maximum value

then have negative values in logarithmic (dB) space.

•

Thresholds T1 and T2 define, in dB, the boundaries of the three regions of the DRC, as referenced to

the rms value of the data into the DRC. Zero-valued threshold settings reference the maximum-valued

rms input into the DRC and negative-valued thresholds reference all other rms input levels. Positive-

valued thresholds have no physical meaning and are not allowed. In addition, zero-valued threshold

settings are not allowed.

CAUTION

Zero-valued and positive-valued threshold settings are not allowed and cause

unpredictable behavior if used.

•

Offsets O1 and O2 define, in dB, the attenuation (cut) or gain (boost) applied by the DRC-derived gain

coefficient at the threshold points T1 and T2, respectively. Positive offsets are defined as cuts, and

thus boost or gain selections are negative numbers. Offsets must be programmed as 32-bit (9.23

format) numbers.

•

Slopes k0, k1, and k2 define whether compression or expansion is to be performed within a given

region, and the degree of compression or expansion to be applied. Slopes are programmed as 28-bit

(5.23 format) numbers.

3.8.1

DRC Implementation

The three elements comprising the DRC include: (1) an rms estimator, (2) a compression/expansion

coefficient computation engine, and (3) an attack/decay controller.

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