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SSM2120 Datasheet(PDF) 11 Page - Analog Devices |
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SSM2120 Datasheet(HTML) 11 Page - Analog Devices |
11 / 12 page 11 5/90, Rev. B1 SSM-2120/SSM-2122 DYNAMIC RANGE PROCESSOR/DUAL VCA DYNAMIC FILTER WITH DOWNWARD EXPANDER A composite single-ended noise reduction system can be real- ized by a combination of dynamic filtering and a downward ex- pander. As shown in Figure 14, the output from the wideband detector can also be connected to the +V C control port of the second VCA which is connected in series with the sliding filter. This will act as a downward expander with a threshold that tracks that of the filter. Although both of these techniques are used for noise reduction, each alone will pass appreciable amounts of noise under some conditions. When used together, both con- tribute distinct advantages while compensating for each other’s deficiencies. Downward expansion uses a VCA controlled by the level detec- tor. This section maintains dynamic range integrity for all levels above the user adjustable threshold level. As the input level decreases below the threshold, gain reduction occurs at an in- creasing rate (see Figure 15). This technique reduces audible noise in fade outs or low level signal passages by keeping the standing noise floor well below the program material. This technique by itself is less effective for signals with predomi- nantly low frequency content such as a bass solo where wide- band frequency noise would be heard at full level. Also, since the level detector has a time constant for signal averaging, per- cussive material can modulate the noise floor causing a “pump- ing” or “breathing” effect. The dynamic filter and downward expander techniques used to- gether can be employed more subtly to achieve a given level of noise reduction than would be required if used individually. Up to 30dB of noise reduction can be realized while preserving the crisp highs with a minimum of transient side effects. FIGURE 14: Dynamic Filter with Downward Expander FIGURE 15: Typical Downward Expander I/O Characteristics at –30dB Threshold Level (1:1.5 Ratio) +20 +20 –30 –30 –40 –45 –60 –75 –50 -60 + – RIN2 REC IN IN |IIN| LOG AV CAV2 1.5M Ω + 1k Ω V– + – RIN1 IN |IIN| V+ LOG AV CAV1 V– 1.5M Ω + 1k Ω V– 39k Ω 5.6k Ω CON OUT 39k Ω 12k Ω 200 Ω +VC –VC 200 Ω 200 Ω 200 Ω – + 36k Ω SIGNAL OUTPUT 36k Ω 36k Ω 36k Ω DOWNWARD EXPANDER 100pF NOISE FILTER THRESHOLD V+ V– FC = 5kHz FC ≤ 20Hz REC IN V+ V– CON OUT 160k Ω 160k Ω +VC –VC 12k Ω – + – + 47 Ω 2200pF SIGNAL INPUT 36k Ω 47 Ω 36k Ω 2200pF OBSOLETE |
Similar Part No. - SSM2120_15 |
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Similar Description - SSM2120_15 |
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