Description
Keeley Compressor Pro
Keeley Compressor Pro.  The stomp-box sized compressor/limiter is made in Oklahoma, USA and engineered to be an indispensable tool for your musical endeavors.  It is in no way limited to be used with only guitar.  It has been designed to work as a studio compressor accepting any range of inputs and a frequency response and noise level matching the finest compressors made.
 
Introduction of Features
Compression LED Display – 7 Segment LED display for fast and accurate metering of compression and gain reduction.  Gain Reduction Levels of -1dB to -20dB are indicated.
Threshold LED Indicator – Bi-Color LED to indicate when compression is initiated and released.
Exact RMS Analysis (ERA) – Senses the true RMS value of the input program material such as your guitar, bass or drum machine.
Hard/Soft Knee Compression – Hard Compression for limiting or adding sustain, soft knee or Komfort Kompression for gentle compression, keeping performances lively and natural sounding without potential phase issues in parallel, or blending style compression.
Auto Mode – Program dependent Attack and Release times.  Set to Auto ON for worry-free performance and automatic Attack and Release times.
True-Bypass – No tone or signal loss when OFF
General Compressor Usage
The Keeley Compressor Pro is designed to be used at home or in the studio for creating full sounding recordings of any instrument.  In live situations, the Compressor Pro can be used to achieve full sounding, polished performances as well as protect amplifiers and speakers from overload.  The Comp Pro is designed to work with any instrument from voice and guitar to keyboard, bass, or drums.  Use it when creating a podcast or YouTube videos to maintain professional performance levels.  Use it around the home to create tons of sustain while at low volumes or low gain settings!
Device Controls
THRESHOLD, RATIO, ATTACK, RELEASE, GAIN, KNEE, & AUTO
THRESHOLD Control and LED – This is probably the most important control on the Comp Pro.  It is adjusted to determine when the compressor is working or when sound is being passed through unaffected.  The Threshold control is turned down or CCW until the THRESHOLD LED turns Red as you play your instrument.  When the THRESHOLD LED turns Red the Comp Pro is actively compressing your signal.  If the LED is Green, the Comp Pro is not compressing and sound is passed through unchanged.
Range of Adjustment is from -50dBu to +10dBu.  2.45mVRMS to 2.45VRMS – Pro Audio (studio) Levels are +4dBu Consumer Audio Levels are -10dBu.  Passive guitar or bass pickups are typically about -25dBu to 2.5dBu.
RATIO Control – “the Compression Knob”, Ratio is the amount of compression you set the Comp Pro for.  You can set it from No Compression (1:1) when all of the way off or CCW.  You can set it as high as Infinite Compression (∞:1) which means that the output level will never increase in output level no matter how loud the input.  This type of setting can be used for hard-limiting to protect recording or speakers or in some cases for guitar effects like chicken-pickin’.
ATTACK Control – Attack Times between 0.15ms and 150ms.  Controls the time it takes for the Comp Pro to start compressing.
RELEASE Control – Release Times between 0.1s to 3s.  Controls the time before the Comp Pro releases or stops compression .
GAIN Control – This is the output level of the compressor.  It does not affect the compression controls like THRESHOLD, RATIO, ATTACK or RELEASE.  It is for make-up gain if you set for heavy compression gain reduction.  +20dB of boost is possible.
KNEE Switch – Hard Knee/Soft Knee.  Hard Knee Compression follows a hard fast rule: If THRESHOLD is met, then Compress at this RATIO.  Soft Knee is Komfort Kompression.  It’s a way to keep compressed guitar or instrument parts sounding lively and dynamic, without the “blanket” of compression found in many types of compressors.
AUTO Switch – OFF/ON – Set to ON in most cases for automatic setting of Attack and Release Times.  This will sound natural and work in a very large number of cases.  The Comp Pro looks at the input signals like guitar, bass, vocals or drums and determines the correct attack and release times depending on what you’re playing and what signal levels are being detected.
 
Details 
https://robertkeeley.com/product/keeley-compressor-pro-namm-2015/