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STA320

5.11.2Limiter 1 Attack/Release Threshold

5.11.3Limiter 2 Attack/Release Rate

5.11.4Limiter 2 Attack/Release Threshold

The STA320 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 F, bit 0

address 0x05. Each channel can be mapped to either limiter or not mapped, meaning that channel will clip

when 0dBFS 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. It is recommended in anti-clipping

mode to set this to 0dBFS, which corresponds to the maximum unclipped output power of a DDX amplifier.

Since gain can be added digitally within the STA320 it is possible to exceed 0dBFS or any other LxAT

setting, when this occurs, 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 reg-

ister 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 a 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 thresh-

old, the gain is again increased at a rate dependent upon the Release Rate register. The gain can never

be increased past it's 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 dynamic 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.

Figure 5. Basic Limiter and Volume Flow Diagram.

D7

D6

D5

D4

D3

D2

D1

D0

L1AT3

L1AT2

L1AT1

L1AT0

L1RT3

L1RT2

L1RT1

L1RT0

0

1

1

0

1001

D7

D6

D5

D4

D3

D2

D1

D0

L2A3

L2A2

L2A1

L2A0

L2R3

L2R2

L2R1

L2R0

0110

1010

D7

D6

D5

D4

D3

D2

D1

D0

L2AT3

L2AT2

L2AT1

L2AT0

L2RT3

L2RT2

L2RT1

L2RT0

0

1

1

0

1001

Gain

Attenuation

Saturation

RMS

Limiter

Gain/Volume

Input

Output