From the Maxon website:
"This new RTC600 Compressor replaces the original Real Tube RCP660 Compressor.
The RTC600 is a studio-grade Tube Compressor Preamp in a compact Stompbox format. The RTC600 uses a precision RMS level Detection circuit and high-performance VCA to create a warm yet bold compression sound with ultra-low noise floor. Its five controls can create a wide variety of effects, including "Brick Wall" limiting and "Soft Knee" compression.
Every aspect of the RTC600 has been re-thought and redesigned to provide a lifetime of trouble-free performance. The tube position comes pre-compression, adding classic valve warmth without increasing the noise level. As soon as power is applied to the pedal, an In-Rush Current control begins heating the tube at a very low voltage (much like a tube amp standby switch) to dramatically extend tube life.
The RTC600 features an internal charge pump circuit that bumps the incoming voltage up to 25 volts, providing massive headroom and full-range frequency response. The RTC600 is perfect for use with any instrument or application and can be sent into an amp's front end, placed in an effects loop, or used as an outboard processor for home recordings.
The RTC600's Front-Panel Controls are as follows -
THRESHOLD - variable between 0 dBu and 40 dBu, allows the user to select the dynamic level at which the compression kicks in.
GAIN - +30 dB of clean Gain allows user to match effect and bypass levels or use RTC600 as a Booster.
RATIO - variable between 1:1 and 1:∞ allows user to control the amount of compression effect.
ATTACK - variable between 20 mS - 600 mS, determines how long it takes for compression to engage after input signal passes the Threshold setting. For more natural attack, set long.
RELEASE - variable between, 140 ms - 700 mS, determines how long it takes for compression to engage after input signal falls below the Threshold setting. For more sustain, set long.
The RTC600 also features a Reduction Status LED that gives a visual indication of compressor function.
Like all Maxon products, the RTC600 features True Mechanical Bypass switching using a 3PDT switch. The RTC600 comes complete with the Maxon AC2009 9-Volt power supply, an auto sensing digital power supply that can be used anywhere in the world.
For studio-quality compression in a compact Stompbox, the RTC600 is the only REAL choice."