AMPLIFIER MODELLING :
In the early days, Multi-effect units only modeled many stomp boxes like Distortions, Delays, Flangers
However in the last five years or so, there was a realisation that a very large percentage of the perceived tone of a
Guitarist stems from the Guitar Amplifier that he uses. This is because older Tube Amplifiers were not ideal designs. They
colored the sound and would be totally unacceptable for use as general purpose PA Amps. However Guitarists used the peculiar
tones of each Amplifier to their advantage. They also abused these Amplifiers by driving them much over their deisred input
signals. They found that some Amplifiers got them unique tones when slightly overdriven or when grossly overfed with signal.
There was also the requirement to simulate Amplifier tones for direct recording purposes.
This lead to research on how to use digital electronics to emulate earlier Amplifiers.
The general concensus was that an Amplifier can be adequately modelled by the following digital building blocks :
Pre- distortion Equaliser : When the guitar signal hits the Amp, the first
thing it sees is the pre-amp. Older preamps were not totally linear. A three or five band Parametric equaliser can
adequately model the total tonal contribution of any active pre-amps inside a Guitar, the tone controls of the guitar and
the pre-amplifier stage of the modelled Amp.
Distortion stage : Each amplifier has a unique distortion. Be it the "clean" tones of an Acoustic
Amplifier, the blues tones of slightly overdriven tube amplifiers, the raunchy "Brit" sounds or the distinctive tones of rectifiers.
Marshalls, Fenders, Engls and Dumbles all have unique distortion characteristics.
The distortion characteristics of Amplifiers can be represented by a non-linear clipping section.
Better Amplifier Modellers realise that real amplifiers distort at each pre-amp and power amplifier stage inside them.
They implement multiple non-linear stages and pass the signal through all these stages to get the final peculiar sound.
Post-distortion Equaliser : Of course all the internal stages mentioned above did not have
flat frequency responses. Hence we need a Post-equaliser. This can be a repeat of the three to five stage parametric equaliser
used for the pre-equaliser, except that the post-equaliser controls the frequency response of the signal after it has been
distorded by the non-linear distorters.
Tone controls : We should not forget that all real amps have tone controls. Most Modellers
represent this with a three knob tone stack or a five band parametric equaliser.
"Equalisation of the signal both before and after the distortion usually has at least as much if not more to do with
how the distortion sounds than the actual method of distortion. One of the most interesting experiments with distortion
most guitarists ever make is to put a multiband graphic equalizer both in front of and behind a distortion pedal. Some time
spent playing with the knobs on this one will give you a whole new outlook on distortion."
As of this writing, Tons of Tones !! ®
is the only Third
Party Amplifier Modelling company that explicitly set the Pre- and Post- equalisers on their Amplifier models and provide
equalisation graphs. This is done on our exclusive MEGS©
So now we see the total picture of the state of the art in Amplifier modelling :
3. Smaller non-linear stages to further shape the waves.
4. A Post-distortion Equaliser section
5. A tone control section
Some Modellers go many steps further and try and emulate also the other quirks of real tube amplifiers : input volume
dependent clipping curves, Compression, Sag, Hum, effects of heating, ghost notes, effects of output transformers etc. It
is debatable on how important are these quirks and how close do the modellers come in modelling these finer points !!