Lexicon Converter manual Non-linear, Transfer Functions

20/20 AD User Guide	Using the 20/20 AD
When RELEASE is set to 0, the compressor acts like an amplifier with a non-	Non-linear
linear transfer function. For example, setting GAIN to 6dB and THRESHOLD to	Transfer Functions
-14dB produces a close approximation of a generic tape saturation curve. This
mode is also useful for overload protection of some types of percussive
instruments.
Note: This function is not available in 4-channel mode.

When recording live music onto 16-bit media, the recording engineer tries to Overload Protection maximize dynamic range by keeping the signal as close as possible to full scale

without actually clipping. Peak levels are typically set a few dB below full scale, because losing a few dB of dynamic range is far preferable to clipping.

The digital compressor eliminates this tradeoff. To use it, first set the input levels to give yourself a comfortable margin between peak level and clipping. For example, to give yourself 4dB of margin, push 1db SCALE and PK HOLD and adjust the input level until the peak reads -4dB (the LED labeled 18).

Now, turn on the compressor . Set GAIN to 4dB. This increases the signal level by 4dB (restoring 0dB peak level ). Set THRESHOLD to 0dB to automatically select the maximum practical ratio.

When an input signal exceeds the peak level by 4dB or less, the compressor gain is automatically reduced just enough to assure that the compressor output never exceeds 0dB. After the overload has passed, the compressor gradually brings the gain back up to 4dB. The RELEASE knob determines the speed of this recovery.

Note: This automatic gain reduction can add considerable distortion to the leading edge of the overload signal. With THRESHOLD set at 0dB (or at any value less than or equal to the GAIN setting), gain reduction will not start until the signal is about to clip — too late to prevent leading edge distortion. If this distortion is unacceptable, try lowering the THRESHOLD setting so that compression starts before the signal clips. If, for example, THRESHOLD is lowered to -8dB, compressor gain reduction will be gradual, instead of being reduced all at once at -4dB.

It is important to remember that the lower you set THRESHOLD, the sooner compression will start, and the more likely you are to color signals which were not in any danger of clipping.

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