The Keeley Compressor is the stompbox for the audiophile. It is a studio grade compressor with the highest grade components to ensure the best sound. The 2 knob has two controls, level and sustain. Also has an internal attack control and input sensitivity control to help utilize this pedal for more than just guitar)
From Keeley 
The finest hand-built compressor on the market today. For years now it has been rated the highest in many “shoot- outs” and has replaced the compressors of many studio pros. The Keeley Compressor uses precision parts to keep the sound quality as close to the original input as possible. Metal film capacitors where harsh sounding ceramic capacitors were used in the original for cost cutting measures. Metal film 1%resistors, Teflonwire, and silver-solderare used throughout. Film capacitors and resistors are used in the audio circuits of many high- end components because of their ability to recreate the fine details of music. Tantalum capacitors are used for filtering and stabilizing as they were in the gray model. Your Keeley Compressor has a 3PDT true bypass switch for perfect tone when off. I hope you enjoy years of music making with your compressor. I know that I have found a renewed interest in playing guitar just because this pedal’s tone.
The Best Placement in the Effects Chain for the Keeley Compressor?
The conventional place for compressors has been the very first thing after your guitar. However, over the past couple years I have convinced players to try it after their main overdrive. The reason for this is your transition from clean to your main overdrive will be pretty smooth and pro-sounding. Most importantly, though, place it before any lead boost pedals such as the Java Boost. Do not place the compressor at the end of your chain or after effects such as delay and echo; it will affect the performance in a negative way.
Input
Standard signal input connection. It is possible to connect this pedal to the output of your overdrive/ distortion pedal. I think it sounds best if you go from your guitar into a tube-sounding distortion and then into the compressor. Experiment and find out what variation gives you the tone or effect you are looking for. Make sure to unplug this jack when not in use. The circuit and battery are active until your cord is unplugged. Also, the main chip in the compressor, the CA3080, is designed for low-level signals only. The compressor will not work as well in the effects loop of an amplifier or after a pre-amp.
Output
Connect this to the input of your amplifier. It is also possible to send this output to a variety of other effects. Please experiment with effect placement in your signal chain to find the sound that defines your playing. I like the compressor after the main overdrive but before pedals you would use for solos or lead boosts.
Sustain
You can use this control to give a sustain effect with almost no increase in noise or high frequency loss. A great starting point is with the control in the 9 O’clock position. This is a great place to start experimenting if you want to run the compressor all of the time as a tone/level shaper. You can get a nice, full effect if you run this control in the 12 O’clock position. I like this position for lead playing. It brings out the note detail. It is also great for funk style playing. It compresses the notes you may play too loud and expands the notes you play too softly.
If you run the control to the 3 O’clock position or greater, you can get a radical sustain effect. Although this position does have some slight increased noise, it allows you to get feedback on demand. It is truly impressive to get a nice, singing feedback at low playing