Universal Audio UAD Plug-Ins ver.7.5 - Manual (Page 474)

UAD Powered Plug-Ins Manual - 474 - Chapter 48: Teletronix LA-2A Leveler Collection
Compress/Limit This switch sets the compression ratio of the leveler. When set to Compress,
the compression ratio is approximately 3:1 and when set to Limit, the ratio is
approximately infinity:1. However, the compression ratios are nonlinear and
frequency dependent, so these figures are not absolute.
Note: Like the original hardware, this control is unavailable on the Teletronix
LA-2 plug-in. The plug-in is “hardwired” in Limit mode.
Emphasis The (R37) Emphasis “set screw” knob controls a shelf filter circuit in the com-
pressor’s sidechain input, thereby enabling frequency-dependent compres-
sion.
When the control is fully clockwise (the default position), the sidechain signal
is unfiltered and all frequencies in the source signal that exceed the compres-
sion threshold will trigger gain reduction equally (within the non-linear con-
straints of the electro-optical characteristics).
Rotating the Emphasis control counter-clockwise increases filtering of the
sidechain signal. The Emphasis filter gradually reduces the lower frequency
content of the sidechain signal, resulting in compression that is less sensitive
to those frequencies, and more sensitive to high frequency content. Therefore,
as the sidechain filtering is increased, higher frequencies are compressed
more.
Note: Emphasis is unavailable on the Teletronix LA-2A Legacy.
Side-Chain Pre-Emphasis (R37) Background
The LA-2A hardware was designed for use in broadcast applications. The au-
dio signal in FM broadcasting undergoes pre-emphasis and results in a 17 dB
boost at 15 kHz. Due to this increase in signal level, transmitters are subject
to over-modulation. The LA-2A hardware provides a control (R37) which con-
trols the amount of high-frequency compression.
This potentiometer is factory set for a “flat” side-chain response (clockwise).
Increasing the resistance of this potentiometer by turning it counter-clockwise
will result in compression which is increasingly more sensitive to the higher
frequencies.