Carl Martin Optical Envelope Filter Carl got a call from an old guitar playing friend who said he didn’t want to use his wah all the time, but wanted to have some of those effects available. Enter the Classic Optical Envelope….essentially a classic envelope filter (auto-wah utilizing the same opto-technology as the Opto-compressor) for guitar or bass, with a bunch of cool options. The first footswitch is for fx on/off (buffered), and the second to select between the three modes (High Pass, Band Pass and Low Pass). Add to this the Level control for overall volume, Drive for how hard the auto-wah will function, Q for adjusting the size of the bandwidth, and Tone which acts as a separate Hi-pass filter, and you have complete control over your fx…from vocal like tones to funky quacks and fat wows! Housed in the cool new diecast housing with mini-knobs and cool retro color, the Classic Optical Envelope can be powered by a 9v battery, but we always recommend a regulated power supply for optimum response!