1

Gain change = 1

× Input signal change

Compression ratio

æ

ö

-

ç

÷

è

ø

(3)

1

24 dB =

1

× 32

4

æ

ö

-

ç

÷

è

ø

(4)

V

-dBV

IN

Increasing

FixedGain

Decreasing

1

:1

2 :

1

4 :1

8 :1

1

:1

2 :

1

4 :1

8 :1

Rotation

Point@

lowergain

Rotation

Point@

highergain

TPA2016D2

The gain change equation is:

Consider the following when setting the compression ratio:

• Dynamic range of the speaker

• Fixed gain level

• Limiter Level

• Audio Loudness vs Output Dynamic Range.

Figure 25 shows different settings for dynamic range and different fixed gain selected but no limiter level.

Figure 25. Output Signal vs Input Signal State Diagram Showing Different Compression Ratio

Configurations with Different Fixed Gain Configurations

The rotation point is always at Vin = 10dBV. The rotation point is not located at the intersection of the limiter

region and the compression region. By changing the fixed gain the rotation point will move in the y-axis direction

only, as shown in the previous graph.

Interaction between compression ratio and limiter range: The compression ratio can be limited by the limiter

range. Note that the limiter range is selected by the limiter level and the fixed gain.

For a setting with large limiter range, the amount of gain steps in the AGC remaining to perform compression are

limited. Figure 26 shows two examples, where the fixed gain was changed.

1. Small limiter range yielding a large compression region (small fixed gain).

2. Large limiter range yielding a small compression region (large fixed gain).

Copyright © 2008, Texas Instruments Incorporated

15

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