FXAlgs #724-6, 728: Distortion
Algorithm Reference-95
MonoD Cab is also similar to Mono Distortion except the hipass is replaced by a full speaker cabinet model.
There is also a panner to route the mono signal between left and right outputs. In MonoD Cab, the distortion
is followed by a model of a guitar amplifier cabinet. The model can be bypassed, or there are eight presets which
were derived from measurements of real cabinets. (See descriptions of FXAlgs #729-732 in this book for more
information.)
Block diagram of MonoD Cab
The distortion algorithm will soft clip the input signal. The amount of soft clipping depends on how high the
distortion drive parameter is set. Soft clipping means that there is a smooth transition from linear gain to saturated
overdrive. Higher distortion drive settings cause the transition to become progressively sharper or ÒharderÓ. The
distortion never produces hard or digital clipping, but it does approach it at high drive settings. When you increase
the distortion drive parameter you are increasing the gain of the algorithm until the signal reaches saturation. You
will have to compensate for increases in drive gain by reducing the output gain. These algorithms will not digitally
clip unless the output gain is over-driven.
Input/Output Transfer Characteristic of Soft Clipping at Various Drive Settings
Signals which are symmetric in amplitude (they have the same shape if they are inverted, positive for negative) will
usually produce odd harmonic distortion. For example, a pure sine wave will produce smaller copies of itself at 3,
5, 7, etc. times the original frequency of the sine wave. In the MonoD EQ, a dc offset may be added to the
signal to break the amplitude symmetry and will cause the distortion to produce even harmonics. This can add a
ÒbrassyÓ character to the distorted sound. The dc offset added prior to distortion gets removed at a later point in
the algorithm.
L Input
Distortion
R Input
Cabinet
Filter
Pan
L Output
R Output
Output
Input
