Lexicon 20/20 AD manual Input

20/20 AD User Guide

Note that the 6dB GAIN setting is given only as an example. Feel free to experiment with any level in this mode. (GAIN settings above 12dB are not available because at that point practically all of the dynamic range of the converter will fit onto 16-bit media. )

Set THRESHOLD to -24dB. Now, when the signal level exceeds -24dB, the gain is gradually reduced until, at 0dB signal level, the compression gain is also at 0dB (unity).

The graph below shows a plot of gain vs. input level with compressor GAIN at 6dB and THRESHOLD set to -24dB. Note that, unlike some compressors, the gain curve is not linear, but changes smoothly. This reduces high-frequency artifacts which can result from aggressive compression.

Threshold

(-24dB)

"0" Level

Output

-104dB
-110dB		"0" Level
	Input

The settings of the GAIN and THRESHOLD knobs determine the compression ratio, according the formula:

ratio = ___ threshold ___

threshold – gain

In our example, the compression ratio is 24⎟ (24 – 6) = 1.33:1. This is not a very intense compression by most standards but, remember, the point is to pack as much music onto the recording media as possible without introducing audible artifacts. As the following table of compression ratios shows, most of the ratios are below 2:1. In order to minimize the audibility of compression artifacts, use ratios from the unshaded portion of the table. Setting the threshold at any level higher than a 4:1 ratio will force the ratio to 4:1.

Using the 20/20 AD

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