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If you’ve used software or hardware amp modelers, chances are you’ve used impulse responses. The technology, developed by Sony at the end of the last century, is one way that modelers mimic various mics, cabinets, rooms, and outboard gear. Impulse responses (IRs) are recordings of test tones created in the spaces or through the gear being modeled. IR reverb players compare these recordings to a theoretically dry version, and then apply the resulting variables to any audio you pump through them. Voilà— your guitar can sound as if it was recorded in the Taj Mahal. Or a sewer. Or through a $5,000 outboard reverb unit.
Most modelers don’t let you load your own IR files, though you can do so using dedicated software plug-ins such as Audio Ease’s Altiverb and Space Designer in Apple’s Logic Pro. And now you can add this technology (also known as convolution reverb) to your pedalboard, thanks to Logidy’s EPSi—the first load-your-own IR stompbox.
EPSi reads IR files from an SD memory card, and ships with a 1 GB card containing hundreds of shareware impulse responses. (Many more are available online.) Quality varies, but with searching and a bit of patience, you can assemble a fine IR library at no cost. (And if you have an IR-making utility, like the ones included with Logic and Altiverb, you can make and load your own IRs.)
EPSi is a solid 4" x 4" stompbox with minimal controls: just a terse, three-character LED, a data knob, an enter button, and a bypass footswitch. To select a new sound, simply scroll to the desired IR number and press enter. Same with altering the reverb time or adjusting the wet/dry mix: scroll and enter. This system works fine, just don’t count on changing tones mid-song, or even mid-set. But hey, even if you use only one IR per show (a nice juicy spring to soak the sound of a no-reverb amp, maybe?), you may find EPSi useful in performance.
But the studio is where EPSi really shines. You have access to hundreds of sounds at once, or even thousands with a larger, pricier memory card. You can also swap between cheaper cards. (You can buy 1 GB cards for less than five bucks each.)
Swapping cards may be a good strategy. There are two versions of the latest EPSi software, which the pedal reads from the SD card along with the IR files. One is optimized for reverbs of up to six seconds, and the other is geared toward mimicking speakers and cabinets. (Yes, you can plug your amp’s direct audio output into EPSi, record direct, and clone the tones of countless cabinet/speaker/mic combinations with startling realism.) To switch software, just power up with the appropriate card inserted. Like most powerful digital effects, EPSi requires AC power, but thankfully an adapter is included.
To learn more about using IRs in the studio, check out the recent PG article "Impulse Control: Mastering Fake Spaces." It covers some extreme sound-design scenarios and includes a link to download some cool and free IR files.