Lexicon
22
Using the 20/20 AD
To summarize:
1. Set the input levels so that the peak level is a few dB below clipping.
2. Turn on the compressor.
3. Set compressor GAIN to the input level safety margin, and THRESHOLD to
0dB.
4. Adjust RELEASE to suit the program material. The faster the expected
clipping source, the faster the release time should be.
5. Adjust THRESHOLD to suit the program material. If the expected source
material is percussive, the chance of clipping is relatively slim, and you don’t
want to color the rest of the music, leave THRESHOLD at 0dB. Otherwise,
it may be necessary to lower the THRESHOLD setting until the clipped signal
sounds acceptable.
Note: The compressor can only prevent clipping if the analog/digital converter
does not overload. Any signal which overloads the converter will also overload
the compressor.
Although the compressor works in both 4-channel and 2-channel mode, the
available dynamic range in 4-channel mode is only a few dB greater than the
capacity of a 16-bit recorder, so nothing is gained by setting your margin greater
than a few dB — unless, of course, there is a specific audio effect you are trying
to achieve.
A slightly unorthodox use of the compressor allows you to automatically fine tune
the level so that the highest peak will be set to exactly 0dBfs when transferring
analog tape (or other repeatable source) to the digital domain.
To do this:
1. Do a dry run of the loudest section(s) of the tape through the 20/20 AD to
check the level. Using 1dB SCALE and PK HOLD, adjust the input level until
the peak comes within 6dB of clipping.
2. Turn on the compressor. Set GAIN to 6dB, THRESHOLD to 0dB, and
RELEASE to infinity. Do another dry run of the loudest section(s) of the tape.
If you turn on DISPLAY, you will see the gain reduction meter grow down
during the peaks and stay down.
3. Rewind the tape, turn on the digital recorder, and play the tape all the way
through. The compressor will add just enough fixed gain to boost the peak
to 0dBfs. Because the gain doesn't change, there are no compression
artifacts.
If you are in 4-channel mode, remember that you have less dynamic range
available, so you should try harder to set the input levels as close to 0dBfs as
practical, only relying on the 20/20 AD for the last 2 or 3dB.
Digitizing Analog Tape
