JAMES SPECTRUM GETS TECHNICAL
Beatmag’s regular technical columnist James Spectrum (AKA Jai Salo of Pepe Deluxe) presents part 2 of his thoughts on the Imperator (check our last issue in Back Issues for Part 1)
Last month I wrote about thermal expansion and Imperator, the first compressor to use miniature light bulbs to control the level of audio. Before I’m gonna tell you about the second generation Imperator, let’s meet another member of the electrical component family, namely LDR. That’s short for Light Dependent Resistor, also known as photoresistor, furthermore known as photocell. An LDR is a variable resistor, its value decreasing with exposure to light. The change in resistance is actually very major, dropping to about 1/100000 of the maximum resistance when very bright light is used. LDRs are used in street lamps to switch them on in the evening and off in the morning as well as in other applications such as flame, smoke and movement detectors, card readers and photographic light meters.
LDR’s are also common in vintage music gear, probably the most famous being Univox Univibe, an effect unit designed to electronically emulate the modulation effects of the rotating "Leslie" speaker.Univibe is sitting boldly on the very top of the short list of ‘Holy Grail’ guitar stomp boxes. Although Jimi Hendrix used Univibe only on a few recordings, for many people Univibe and Jimi are synonymous: a psychedelic sound that’s subtle yet instantly recognizable. Univibe uses a lamp and four LDRs to control its filters, creating a deep and very organic sweeping underwater-like tone. Much of the magic comes from the uneven sweep caused by the lamp going on quicker than it goes off. A less known fact is that Univibe has two somewhat more versatile parents: Vibra-Chorus and Resly-Tone, both featuring a tremolo setting in addition to Univibe’s vibrato and Leslie emulation. Resly-Tone is a good example that contrary to common belief, Japanese engineers can possess a sense of humour: just pronounce the name with a heavy Japanese accent! Vibra-Chorus and especially Resly-Tone are rarer than hen’s teeth, but you can hear the latter in action on the Husky Rescues superb version of Alice Cooper’s ‘Poison’. So, what’s all this gotta do with Imperator? Well, we had a compressor that produces light every time it pulls down an audio peak…so we thought why not use a few LDRs to add some extra features?! At the most basic level, every compressor makes loud sounds softer and soft sounds louder so that the music going through it has a smaller (compressed) dynamic range. The problem is, the human hearing is very frequency dependent, as proved by guys named Fletcher and Munson way back in 1930’s at Bell Labs. The ear is especially sensitive between 1 and 6 kHz. This means that if you take, for example, a drum loop and really crush it with a compressor, the cymbals, heavy on high frequencies, can end up sounding way too loud and annoying. Your million dollar beat magically transformed to kids playing drums in school music classes. Not good. So, what we needed was something to tame the cymbals while not dulling the overall sound. Borrowing the idea of lamp controlled filters from Univibe, we decided to aim at tone controls that would react to the dynamics of the audio signal. Implementation turned out to be surprisingly easy: we took the simplest textbook bass and treble filters (both consisting of one component!), and bypassed them with LDRs that were placed right next to two bulbs inside the Imperator box (providing the necessary nocturnal environment). When there was no loud audio, there was no light from the bulbs, the LDRs would pass no signal, and the filters were ‘closed’. Quieter sounds such as hi-hats were filtered. More light meant more signal bypassing the filters. By adjusting the filter component values and tweaking the Imperator driving the amplifier’s bass and treble controls, we managed to tame the hi-hats and reduce rumble, yet when snare and bass drum hits lit up the lamps, the filters ‘opened’ smoothly, bringing out the glorious full sound. The processed drums were nice and crunchy … and subjectively about three decades older than the original audio. Hear for yourself!
Two unprocessed beats followed by two Imperator Mark II beats.
