Earlier Amplifier designs did not exhibit a flat frequency response.
They also had earlier designs of "tone stacks" that had their own frequency quirks.
These peculiarities made each Amplifier sound unique. Guitarists quickly learnt which Amplifier to use to attain
the sound they wanted.
The famous R.G. Keen notes that the tonal characteristics before and after a distortion stage is equally important in
perceived tone as the actual characteristics of the distortion itself.
For example, suppose we reduce the mids before the distortion stage and then increase it back after the distortion. Now
if we play a chord arpeggio, we will find that all the strings output almost the same volume but the midrange sounds less
fuzzed than the other strings.
Here we look at some of the graphs that MEGS®
outputs when studying Pre-distortion and Post-distortion equalisers of Amplifier Models.
Above we show the Pre-distortion and Post-Distortion curves of the DIRECT model. They are both the same ie flat till
about 8KHz and a boost after that. The resultant total equalisation is shown in bold green.
And above are the Equaliser graphs of the 2101 Clean channel. The pre-distortion equaliser is set at a low level
of -10dB so that most of the frequencies pass undistorted through the non-linear stages. Notice however the hump in the pre-
EQ around 7 KHz indicating that the highs are more distorted.
The Pre- EQ is set flat, with a low rolloff around 100 Hz. The resultant total equalisation is shown in bold red.
And above is the EQ charts for a Model trying to emulate the same Amp when run into saturation. Tube Amplifiers show
different frequency characteristics at different operating points. This is because a large input signal that drives the
tubes into saturation makes heavy demands on the power supply. Its voltage drops, leading to a different bias point for all
Above is the DIGCLEAN model. If you see the graph of this model's non-linear stage
, you will agree that there is hardly any distortion at all. Hence here all the Equalisers do is act like tone controls. This
is the famous "scooped mids" setting where it appears that someone has taken an Ice cream scoop shaped bite out of the mid
Below are some Bass Amplifier Models. You can see that they too exhibit the "Scooped Midrange" equaliser profile. The
Pre-EQ is fairly flat so that most strings are distorted equally, but the Scooped Post-Equaliser gives you that famous sound
Other Amplifier models with Scooped Mids are shown below :
Many other Amplifier Models boost the Mids for their particular sound. Here are some of them.
Each Amplifier Models' particular Pre- EQ and Post- EQ leads to its individual tone. Below are some famous Amplifier
If we compare the equaliser settings in the last two models presented above, we see that they are very similar indeed.
However these models sound distinctly different. Please remember that Pre-Distortion and Post-Distortion Equalizers work in
conjunction with the distortion stage. Hence two amplifier models with the same equalizer settings can sound and behave very
differently based on differences in their Non-Linear Distortion stage
The Equaliser plots for Acoustic guitars simulations are quite different. Acoustic guitars have no distortion but they
show strange resonances bewteen the strings and the hollow body. An Acoustic Guitar simulator tries to recreate these resonances
by odd peaks and dips in the equaliser settings. We show graphs of two different such simulators below.