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STA559BWQS Datasheet(PDF) 49 Page - STMicroelectronics |
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STA559BWQS Datasheet(HTML) 49 Page - STMicroelectronics |
49 / 66 page STA559BWQS Register description 49/66 5.11.4 Limiter 2 attack/release threshold The STA559BWQS 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 STA559BWQS 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 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 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 threshold, 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 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 32. Basic limiter and volume flow diagram. D7 D6 D5 D4 D3 D2 D1 D0 L2AT3 L2AT2 L2AT1 L2AT0 L2RT3 L2RT2 L2RT1 L2RT0 011 0 1 0 0 1 |
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