Datasheet

48/67 Doc ID 18190 Rev 1

6.6.3 Limiter 2 attack/release rate (addr 0x14)

6.6.4 Limiter 2 attack/release threshold (addr 0x15)

6.6.5 Description

The STA559BW 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 night-time listening mode which is often needed for DVDs. The two

modes are selected via the DRC bit in Configuration register E (addr 0x04) on page 31.

Each channel can be mapped to either limiter or not mapped, meaning that channel will clip

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.

Figure 17. Basic limiter and volume flow diagram

The limiter attack thresholds are determined by the LxAT registers.

It is recommended in anti-clipping mode to set this to 0 dBFS, which corresponds to the

maximum unclipped output power of a FFX amplifier. Since gain can be added digitally

within the STA559BW it is possible to exceed 0 dBFS or any other LxAT 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

The limiter release thresholds are determined by the LxRT registers.

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

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

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

01101001

ATTENUATION

SATURATION

RMS

LIMITER

GAIN

GAIN / VOLUME