STA311B datasheet(57/102 Pages) STMICROELECTRONICS

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STA311B

Registers

102

0 dBFS 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 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 STA311B it is

possible to exceed 0 dBFS or any other LnAT 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 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 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 overlimiting 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 threshold 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 9. Basic limiter and volume flow diagram

CnLS[1,0]

Channel limiter mapping

Channel has limiting disabled

Channel is mapped to limiter #1

Channel is mapped to limiter #2

Gain

Attenuation

Saturation

RMS

Limiter

Gain/Volume

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