BSS Audio OPAL Series DPR-944 Owner's Manual - Manual (Page 23)

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In use the threshold and ratio controls are generally adjusted as a pair whilst
listening to the result. The release fast switch also changes the characteristics.
9.3 Ratio
The effect of the ratio control can be shown on a graph which plots input level
against output level, as shown in figure 9.1. This clearly shows that below
threshold the DPR 944 acts purely as a linear amplifier.
In applications where gentle compression is required, it is advantageous to
change from the linear to compression region in a very gradual manner, rather
than the more conventional abrupt manner, as shown in figure 9.2. The DPR
944 has been configured so that for low settings of the ratio control and low
levels of compression, the transfer is soft, and for increasing ratio settings and
high levels of compression the transfer becomes harder. This ‘progressive
knee’ gives inaudible compression for low levels of ratio and gain reduction,
whilst allowing harder compression for effective limiting and extreme control
when required.
The ‘progressive knee’ is an important characteristic of the DPR 944 (and all
other BSS Audio compressors) and is why a ‘soft knee’ or other similarly
labelled control is not required. Progressive knee is also one of the main
reasons for the transparency and musicality of the unit at low compression
ratios.
Fig 9.1 Effect of Ratio