ReleaseTime

E

Limiterthreshold

GAIN

A

C

B

D

AttackTime

Limiterthreshold

Limiterthreshold

HoldTime

Limiterthreshold

TPA2016D2

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 20 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 20. Input and Output Audio Signal vs Time

Since the number of gain steps is limited the compression region is limited as well. The following figure shows

how the gain changes vs. the input signal amplitude in the compression region.

12

Copyright © 2008, Texas Instruments Incorporated

Product Folder Link(s): TPA2016D2