TAS5518 datasheet(34/103 Pages) TI

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Introduction

SLES115 — August 2004

TAS5518

7 Biquads

in Series

Bass and

Treble

Bass & Treble

By-Pass

Bass & Treble

In-Line

Loudness

DRC

In-Line

DRC

By-Pass

From Input Mixer

Max

Volume

Pre-

Volume

Post-

Volume

Channel

Volume

Master

Volume

To Output

Mixer

Figure 1−19. DRC Positioning in TAS5518 Processing Flow

Figure 1−20 illustrates a typical DRC transfer function.

DRC Input Level

1:1 Transfer Function

Implemented Transfer Fucntion

Region

Figure 1−20. Dynamic Range Compression (DRC) Transfer Function Structure

The three regions shown in Figure 1−20 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.

•

The samples input into the DRC are 32-bit words and consist of the upper 32 bits of the 48-bit word format

used by the digital audio processor (DAP). The 48-bit DAP word is derived from the 32-bit serial data

received at the serial audio receive port by adding 8 bits of headroom above the 32-bit word and 8 bits

of computational precision below the 32-bit word. If the audio processing steps between the SAP input

and the DRC input result in no accumulative boost or cut, the DRC would operate on the 8 bits of headroom

and the 24 MSBs of the audio sample. Under these conditions, a 0-dB (maximum value) audio sample

(0x7FFFFFFF) is seen at the DRC input as a –48-dB sample (8 bits x −6.02 dB/bit = −48 dB).

TAS5518 Datasheet(PDF) 34 Page - Texas Instruments

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