You may be familiar with the Aphex line of Exciter pedals designed specifically for live applications, but the latest in their pedal range is an optical compressor called the Punch Factory. This all-analogue design uses true optical (lamp and photocell) gain control and, unlike the vast majority of pedals, it has a gain-reduction meter on the top panel so that you can see how much gain reduction is being applied. The unit is designed with guitar players in mind (both electric and electroacoustic, as well as bass), but the inclusion of an Active/Passive input switch means that instrument-level signals can also be accommodated, making it practical to process synths and other electronic instruments.
On the top of the orange cast-metal case is a traditional latching footswitch that bypasses the unit completely (though it leaves the gain-reduction meter working) as well as a red status LED that shows when the unit is active. A Drive knob sets the amount of compression, while Volume allows the compressed signal level to be set relative to the bypassed level. There are no envelope or ratio controls — just the Drive knob to set how much compression you want. So that you know how much gain reduction is being applied, the multi-segment gain-reduction meter is calibrated from zero to 20dB.
The power is switched on automatically when a jack is inserted into the input socket, and when it comes to power you're spoilt for choice: you can use a 9V battery, virtually any PSU over 5V (AC or DC) that will fit the socket, or phantom power via the balanced XLR output. This XLR out, combined with a ground-lift switch, means that the Punch Factory also doubles as a very effective DI box. A switch sets the XLR output to be either compressed (when the compressor is active) or always uncompressed, though the instrument-level jack output always follows the bypass-switch status. Battery life is estimated to be between 100 and 150 hours, so unless you leave it plugged in by mistake the battery should last a long time.
The optical compression circuit is designed to increase sustain and reduce dynamic range without drastically affecting the attack characteristics of the instrument being processed, so you don't hear that 'sucking' sound that some compressors produce. This can be achieved because of the complex and nonlinear way in which optical gain-reduction devices work, so you get all the benefits of compression without the typical disadvantages. Some optical sensors also exhibit a memory effect, so that they react more strongly when they receive multiple pulses (signals above the threshold) than they do if they only receive one or two of the same level, and this again helps produce a subjectively even sound.
The nominal compression ratio is set at 3.7:1, and up to 30dB of gain reduction is available. Having a choice of input settings (10M(omega) for passive or 50k(omega) for active) means a wide range of mono sources can be accommodated, and the frequency response extends up to 30kHz, so you won't be losing any top end. The DI output impedance is 150(omega), so long cables can be driven without problem.
This compressor is so smooth sounding that some users have mistakenly assumed their units weren't working and taken them back to the shop! However, if you set the Level control so that the peak sound is the same whether bypassed or not, and if you set Drive to show more than say 6dB of gain reduction, you can clearly hear that the sound is more even and sustains longer. On acoustic guitar, I felt the sound was just about right for recording, where the processing seemed to improve the perceived sound quality and evenness of tone without obviously changing the basic sound. With electric guitar, it provided a great way to get more sustain from an amp or preamp at lower overdrive settings, again without losing any of the instrument's natural jangle. Indeed, although the controls are as simple as they possibly could be, this is probably the nicest compressor pedal I've heard to date. And yes, I did end up buying one!