Manual

2500+ Bus Compressor API
13
SOFT: Rounded response curve
• Gradual onset of compression (fade-in up to the set ratio)
• Similar to an “over-easy” type knee
• More transparent
• The green LED illuminates when engaged
5.1.2 THRUST
®
The 2500+ 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 THRUST
®
circuit can be engaged using the THRUST
®
switch.
THRUST
®
: Cycle to select the THRUST
®
function
• LOUD: Inserts the LOUD THRUST
®
filter before the RMS detector
o Red LED
• MED (Medium): Inserts the MED THRUST
®
filter before the RMS detector
o Yellow LED
• NORM (Normal): No THRUST
®
filter before the RMS detector (flat)
o Green LED
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 Pro6 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