STA326

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7.12.2 Limiter 1 Attack/Release Threshold (Address 13h)

7.12.3 Limiter 2 Attack/Release Rate (Address 14h)

7.12.4 Limiter 2 Attack/Release Threshold (Address 15h)

7.12.5 Dynamics Control Description

The STA326 includes 2 independent limiter blocks. The purpose of the limiters is to automatically reduce

the dynamic range of a recording to prevent the outputs from clipping in anti-clipping mode, or to actively

reduce the dynamic range for a better listening environment (such as a night-time listening mode, which

is often needed for DVDs.) The two modes are selected via the DRC bit in Configuration Register D, bit

5 address 0x03. Each channel can be mapped to Limiter1, Limiter2, or not mapped.

If a channel is not mapped, that channel will clip normally when 0 dB FS is exceeded. Each limiter will

look at the present value of each channel that is mapped to it, select the maximum absolute value of all

these channels, perform the limiting algorithm on that value, and then if needed adjust the gain of the

mapped channels in unison.

The limiter attack thresholds are determined by the LxAT registers. When the Attack Thesehold has been

exceeded, the limiter, when active, will automatically start reducing the gain. The rate at which the gain

is reduced when the attack threshold is exceeded is dependent upon the attack rate register setting for

that limiter. The gain reduction occurs on a peak-detect algorithm.

The release of limiter, when the gain is again increased, is dependent on a RMS-detect algorithm. The

output of the volume/limiter block is passed through an RMS filter. The output of this filter is compared to

the release threshold, determined by the Release Threshold register.

When the RMS filter output falls below the release threshold, the gain is increased at a rate dependent

upon the Release Rate register. The gain can never be increased past its set value and therefore the

release will only occur if the limiter has already reduced the gain. The release threshold value can be used

to set what is effectively a minimum dynamic range. This is helpful as over-limiting can reduce the dynam-

ic range to virtually zero and cause program material to sound “lifeless”.

In AC mode the attack and release thresholds are set relative to full-scale. In DRC mode the attack thresh-

old is set relative to the maximum volume setting of the channels mapped to that limiter and the release

threshold is set relative to the maximum volume setting plus the attack threshold.

D7

D6

D5

D4

D3

D2

D1

D0

L1AT3

L1AT2

L1AT1

L1AT0

L1RT3

L1RT2

L1RT1

L1RT0

011

0

1

0

0

1

D7

D6

D5

D4

D3

D2

D1

D0

L2A3

L2A2

L2A1

L2A0

L2R3

L2R2

L2R1

L2R0

01101010

D7

D6

D5

D4

D3

D2

D1

D0

L2AT3

L2AT2

L2AT1

L2AT0

L2RT3

L2RT2

L2RT1

L2RT0

011

0

1

0

0

1