Before answering the question “what is an optical compressor,” maybe we should ask “what is a compressor?” A compressor reduces dynamic range, the difference in signal level between the loudest and quietest signals. This can be used to prevent loudly played notes from jumping too far out and above other instruments in a mix. It can also keep loud passages from causing overloading or unwanted clipping (distortion). In addition to solving these sorts of problems, compression can also be used as an effect. Compressors often include a make-up gain circuit before their output to bring back overall signal level that was diminished by the initial gain reduction of the loudest signals. This effectively brings up the signal of quieter passages, which is why when it comes to guitar (especially), compressors are associated with sustain. The attack of a note has its gain is reduced, so the decay of the note is now louder relative to the attack, increasing sustain.
So what about optical compression? There are different types of compression circuits (including optical, FET, VCA, and variable-MU) that have been used to create classic compressors that each shine in different applications and for various styles and esthetics. In an optical compressor, electricity (from the audio input signal) is converted into light, and the intensity of that light is registered by a sensor which controls the amount of gain reduction. The louder the input signal, the brighter the light, and the brighter the light, the more the gain is reduced. Imperfections can be beautiful, and the non-linearities in this analog system contribute to a sound that is often described as musical and natural. Also, optical compression circuits typically have a somewhat slower response than some other methods (such as FET compression). This allows attacks to remain well-defined and for clarity to be maintained even at relatively high compression levels. A couple of the most famous optical compressors of all time are the Teletronix LA-2A and the TUBE-TECH CL 1B.
By incorporating premium all-analog optical compression often found in studio racks into a guitar pedal, OB.1 allows guitarists and bassists to naturally and musically smooth out their overall signal, increase sustain, and bring out softly-played notes so that even the fastest passages are delivered cleanly and evenly. In addition to studio quality, beautifully transparent analog optical compression, OB.1 also includes a switchable Clean Boost with EQ curves designed to super-charge your favorite amp and reveal its true character.
Featuring an all-analog signal path with premium components throughout and very low noise circuitry, OB.1 is perfect for the number one spot in your signal chain. OB.1 also allows you to enjoy the sustain of high gain without too much of the fizzy stuff. And OB.1’s extremely quiet signal path with its high-quality, low noise op amp and high-impedance input is perfect in front of your high-gain setup.
Many distortion pedal circuits and high gain guitar amp channels yield best results if superfluous bass frequencies are filtered prior to the high gain stage(s). The frequency of the low E string on a guitar is 82.41 Hz. With these two facts in mind, OB.1 was designed to start rolling off bass frequencies at about 80Hz, for optimal interaction with high-gain guitar preamp and drive pedal circuits. However, OB.1 is also available without this filtering. For those who want to use OB.1 with bass, the pedal is available with a Bass Guitar Modification, which removes the high-pass filtering, thereby expanding the low-end range. With the optional Bass Guitar Modification, OB.1 offers the smooth, musical compression sought after by professional bassists on stage and in the studio.