ReleaseTime

E

Limiterthreshold

GAIN

A

C

B

D

AttackTime

Limiterthreshold

Limiterthreshold

HoldTime

Limiterthreshold

14

TPA2026D2

SLOS649B – MARCH 2010 – REVISED MAY 2016

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Feature Description (continued)

Table 2. TPA2026D2 AGC Variable Descriptions (continued)

VARIABLE

DESCRIPTION

Compression Ratio

The relation between input and output voltage.

Noise Gate Threshold

Below this value, the AGC holds the gain to prevent breathing effects.

Attack Time

The minimum time between two gain decrements.

Release Time

The minimum time between two gain increments.

Hold Time

The time it takes for the very first gain increment after the input signal amplitude decreases.

The AGC works by detecting the audio input envelope. The gain changes depending on the amplitude, the limiter

level, the compression ratio, and the attack and release time. The gain changes constantly as the audio signal

increases and/or decreases to create the compression effect. The gain step size for the AGC is 0.5 dB. If the

audio signal has near-constant amplitude, the gain does not change. Figure 32 shows how the AGC works.

A.

Gain decreases with no delay; attack time is reset. Release time and hold time are reset.

B.

Signal amplitude above limiter level, but gain cannot change because attack time is not over.

C.

Attack time ends; gain is allowed to decrease from this point forward by one step. Gain decreases because the

amplitude remains above limiter threshold. All times are reset

D.

Gain increases after release time finishes and signal amplitude remains below desired level. All times are reset after

the gain increase.

E.

Gain increases after release time is finished again because signal amplitude remains below desired level. All times

are reset after the gain increase.

Figure 32. Input and Output Audio Signal vs Time