Kemper Profiling Amp - a thousand flawless guitar amps in a box
By Vincent Rice
August 25, 2011
Musicians are generally liberal souls but when it comes to their equipment they can be ultra-conservative - particularly guitarists. Getting their personal 'tone' and a particular 'feel' from a system of wood, wire, pickups, effects pedals, amplifiers and speakers can become a life-long struggle of incremental experimentation and bouts of pure voodoo. Over the decades certain combinations of (usually) tube amplifiers and speakers recorded using certain microphones have become known standards that feature heavily in everybody's record collection. It can be a prohibitively expensive however to keep a stable of classic tube amplifiers and, since the late 90s, the holy grail of music technology companies like Line 6 and others has been to digitally re-create these amplifiers so that hundreds of iconic tones could be stored in one box and used in the studio or live.
Unfortunately, the dynamic behavior and feel of a tube amp is an extremely complex system to understand and while many thousands of guitar amp modellers have been sold due to the sheer convenience, they could not be said to be entirely convincing. The very best available today, the stunning AxeFX from Fractal Audio, has required the mathematical modelling of almost every single component (resistors, capacitors, tubes, transformers etc.) and their interactions within a guitar amp plus the addition of some special 'chaotic' maths (hence the company name) to create credible sounds in a somewhat expensive and complex unit. In September, a new product will hit the streets that aims to do away with that complexity and within 30 seconds perfectly re-create any guitar amplifier.
Christoph Kemper is not exactly new to making digital circuits sound analog. For fifteen years his company has been making one of the finest sounding series of digital synthesizers, the Access Virus. Although not a guitarist, Christoph had always been fascinated by guitar distortion and a few years ago decided to try and finally accurately re-create a distorting guitar amplifier digitally. Rather than take the component modelling route like programmer Cliff Chase at Fractal, he and his team looked for a dynamic form of convolution (the digital imposition of one signal's characteristics onto another that is used a lot in reverberation simulations).
After a couple of years they were able to parametize what actually needed to be simulated to re-create the dynamic behavior of a tube and it's surrounding circuits. The problem was that the equations were so complex it would take an age just to model one amplifier, never mind a collection. It was at this point that Christoph decided that the amplifier being simulated could solve those equations itself and the concept of an amp 'profiler' was born, though it was another two years before a working system was produced.
To profile a given amplifier with the rather splendid-looking (and definitely Germanic) Kemper Profiling Amp you simply play through the Kemper into your amp and adjust eq, speakers, mics etc. until you have the sound you want coming out of your studio monitors. The Kemper is fed back that finished sound and switched to profiling mode. In that mode it puts a number of strange sounds through the amp chain - a low frequency 'wobble' sweep that gets louder and louder. This signal enables measurement of the dynamic behavior, frequency response and distortion of the amp. A second signal, a collection of higher frequency sine waves, allows the measurement of intermodulation distortion. When that is compared to the original sine waves a number of equations can be solved for the frequency response of the speaker on it's own. Very clever stuff and of course much of the process will remain clouded in mystery for commercial reasons.
When the process is complete, in around 30 seconds, you can immediately compare playing through the Kemper model to your original amplifier with the press of a button - something that no other amp simulator gives you. In demonstrations the sound of the two is spookily close. But there's more. Because the process separates out several amplifier parameters those characteristics can be manipulated well beyond what a physical amp would be capable of. The gain and distortion of relatively clean amps can be pushed, power "sagging" can be manipulated for a more modern or vintage feeling amplifier. The guitar pick sound portion can be increased or the amp compressed for greater sustain. The speaker cabinet size and tone can be manipulated independently and there are of course a set of traditional Bass Middle Treble Presence tone controls.
Rounding off the features are four virtual effects pedal slots before the amp sim, modulation, delay and reverb slots after the amp sim and an external effects loop to provide a complete guitarist's rig.
As you might imagine there is considerable excitement amongst guitarists to see whether the Kemper Profiling Amp performs as promised. The possible downsides are the "handbag/lunchbox" form-factor, that you really need access to a decent studio set-up to profile amplifiers properly (though of course a whole collection of amp profiles will be supplied with the unit), and the price, which at a projected US$1,900/1,900 euro is a little more than was originally suggested and not far off from the deeply capable AxeFX2 at $2,600. That said, the AxeFX is made in relatively small numbers and is only available directly from the manufacturer. The Kemper will be mass produced and the price projected is the full retail so street prices will be lower. If this unit truly feels like a classic tube guitar amp to play then it will represent something of a seismic shift in the conservative world of guitar gear.
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