TAS5548DCAR datasheet(40/118 Pages) TI2

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DRC Input Level

1:1 Transfer Function

Implemented Transfer Function

Region

M0014-01

TAS5548

SLES270A – NOVEMBER 2012 – REVISED APRIL 2015

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Figure 37. Dynamic Range Compression (DRC) Transfer Function Structure

The three regions shown in Figure 37 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.

7.4.16.1 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.

•

RMS estimator—This DRC element derives an estimate of the rms value of the audio data stream into the

DRC. For the DRC block shared by Ch1 and Ch2, two estimates are computed—an estimate of the Ch1

audio data stream into the DRC, and an estimate of the Ch2 audio data stream into the DRC. The outputs of

the two estimators are then compared, sample-by-sample, and the larger-valued sample is forwarded to the

compression/expansion coefficient computation engine.

Two programmable parameters, ae and (1 – ae), set the effective time window over which the rms estimate is

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