The “compression” control affects two characteristics of the compression action, namely: “ratio” and “threshold.” The threshold is a predetermined reference voltage that can be used to determine the parts of a guitar signal that require compression. When below this threshold the guitar signal is permitted to pass through the pedal’s circuitry unaffected. However, as soon as peak transients exceed the predetermined voltage, the compressor circuitry kicks in. By effectively reducing the pedal’s gain the amplitude of the peak is instantaneously reduced.

Signal reduction can be subtle or more extreme, depending on the amount of gain reduction applied for a given peak in the input voltage. This pretty much defines the term ratio (i.e. amount of gain reduction relative to input peak).

This control also increases the make-up gain in synchrony with the ratio and threshold levels. Without this the overall level of the pedal would drop on higher compression settings. This means that sounds can be quickly dialled in without the need to play around with a separate gain control. Naturally, it also means that any background noise will become more apparent on extreme settings as the overall gain will be very high prior to gain reduction.

GAIN REDUCTION INDICATOR
This led will light up when attenuation is taking place. This is useful as it provides visual feedback to the user – allowing them to see, in a clear and concise way, the results of tweaking pedal settings.

HIGH/LOW SWITCH
The “high/low” switch lets the user choose between two overall levels of ratio. In the low position the ratio is similar to that of many classic guitar-orientated compressors. In the high position the effect is more pronounced - creating loud, percussive attack transients at the start of each note (on slow attack times), or completely replacing attack transients with dips in volume, as the gain is immediately reduced by an excessive amount (on fast attack times).

ATTACK
”Attack” determines how quickly the gain reduction kicks in after the initial detection of a peak transient. Slower attack times will result in a percussive quality being added to the natural transients of both chords and single notes. This is because for a short instant the gain reduction doesn’t engage and the note is momentarily amplified by the un-attenuated make-up gain. These short but loud transients will be limited by the cool tube as the valve enters its non-linear region. With fast attack times the gain reduction is introduced immediately and transients are quickly reduced. The attack time is shortest with the dial turned fully anti-clockwise and increases as the dial is turned clockwise.

RELEASE
“Release” determines the amount of time during which the gain is attenuated. Consider the case with no, or very little release time. Once triggered, the gain reduction will remain intact until such a point as the input peak has passed. i.e. the gain reduction is purely influenced by the nature of the program material (in this case the guitar). The user may set a release time in order to hold the gain at the attenuated level, for a finite period of time (regardless of any reduction in input signal – However, subsequent peaks can trigger greater gain reduction during this time.). The release control can be adjusted with greater release times being heard as the control is turned clockwise. Perhaps the easiest way to evaluate release time is to play a short and loud dampened chord and observe the amount of time it takes for the compression indicator to switch off.

HIGH-END EMPHASIS
This control simply fine tunes the amount of compression applied to the “top-end” of the guitar’s signal. This is done by using a filter to either boost or cut the higher frequencies present in the “side-chain” circuit (i.e. the signal that drives the “opto”/compression device). In the centre position the frequency response of this filter is flat. As you turn the dial anti-clockwise, high frequencies are cut, and so the compression to the “high-end” is reduced. The treble now rings-out above the bass – giving chord parts greater jangle! Turning the control clockwise from the centre position boosts the high frequencies, producing even greater compression. Overall dynamics are flattened and “digging-in” to lead parts produces very pronounced compression effects.

VOLUME
This control simply adjusts the amount of signal coming out of the pedal.