API Audio THE BOX - Manual (Page 55)

API “The BOX” Operator’s Manual
55
THRUST ®
The 527 compressor includes API’s patented THRUST
® circuit that can be switched in
or out as needed. This places the THRUST ® filter before the RMS detector that
decreases the compressor’s reaction to low frequency content. The result is a
noticeable increase of punch and low frequencies, but a uniformly compressed signal.
It’s the “little more punch” switch!
The patented THRUST ® circuit has been used for many years in the famed API 2500
Stereo Compressor, ATI Paragon and Paragon II consoles, as well as the Pro-6 Input
Strip. This circuit places a filter in front of the RMS detector with a slope of 10dB per
decade (-3dB/8va), which is the inverse of the pink noise energy curve. In acoustics,
the pink noise curve is used to equalize energy vs. frequency over the audio spectrum,
as sound requires more low frequency energy than high frequency energy to sound
correct to your ear. In Hi-fi equipment, a “LOUDNESS” contour is used to equalize the
music at lower levels so it sounds correct. Even with this curve, there is still a
substantial amount of low frequency information compared to high frequency
information in the audio signal path. When that signal is fed into the RMS detector, the
detector will process the signal into a DC control voltage based upon the those louder
low frequencies, resulting in a control voltage that favors the low frequencies of the
signal, causing pumping and a loss of punch. Sometimes, this is not desirable. By
engaging the THRUST
® switch, this inverse filter is placed in front of the RMS
detector, evening out the energy by lowering the energy in the low frequencies and
increasing the energy in the high frequencies, so each octave has the same energy
instead of each octave having half the energy as the one lower. This creates a unique
compression effect that still reduces the overall gain, but the sound is much more
punchy and the signal actually sounds less compressed.
THRUST ® : Inserts the THRUST ® filter before the RMS detector
•
Illuminates when engaged