STA321MPL1 datasheet(43/80 Pages) STMICROELECTRONICS

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STA321MPL1

Registers

5.2.45

Limiter 1 attack/release threshold (0x30)

5.2.46

Limiter 2 attack/release rate (0x31)

5.2.47

Limiter 2 attack/release threshold (0x32)

5.2.48

Limiter description

The STA321MPL1 includes two 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 nighttime listening mode which is often needed for DVDs. The two

modes are selected via the DRC bit in configuration register B, bit 7 address 0x02. Each

channel can be mapped to either limiter or not mapped, meaning that the channel clips

when 0 dBFS is exceeded. Each limiter looks at the present value of each channel that is

mapped to it, selects the maximum absolute value of all these channels, performs the

limiting algorithm on that value, and then, if needed, adjusts the gain of the mapped

channels in unison.

The limiter attack thresholds are determined by the LnAT registers. It is recommended in

anti-clipping mode to set this to 0 dBFS, which corresponds to the maximum unclipped

output power of an FFX amplifier. Since gain can be added digitally within the STA321MPL1

it is possible to exceed 0 dBFS or any other LnAT setting. When this occurs, the limiter,

when active, automatically starts 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 the limiter, when the gain is again increased, is dependent on an 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

increased at a rate dependent upon the release rate register. The gain can never be

increased past its set value and therefore the release only occurs 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 overlimiting can reduce the dynamic range to

virtually zero and cause program material to sound lifeless.

L1AT3

L1AT2

L1AT1

L1AT0

L1RT3

L1RT2

L1RT1

L1RT0

101

L2A3

L2A2

L2A1

L2A0

L2R3

L2R2

L2R1

L2R0

101

L2AT3

L2AT2

L2AT1

L2AT0

L2RT3

L2RT2

L2RT1

L2RT0

101

STA321MPL1 数据表(PDF) 43 Page - STMicroelectronics

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