The homework in Chapter 19 asks you to design a fuzz face emulator using the graphs in Figure 19.7e. I understand the concept:
1)find a nonlinear function that replicates the simulation output waveform and distortion harmonics .
2)apply filters to emulate the frequency response of the circuit.
The problem is: how do I find this nonlinear function ?
For point 2) just look at the frequency response of spice and design a digital filter with those characteristics.
But for point 1? Do you have to use a combination of the functions given in the book ? How do I find the "custom" function to replicate the output of the fuzz face? Solved this problem I can, in theory, replicate the output of many other circuits!
This homework problem is designed to be completely open-ended. It was a request from another professor when I did the book proposal, to have this kind of question where the students and their professors could work on different solutions, none of them being ideal.
The main thing about the Fuzz Face is how it changes the duty cycle of the waveform. With an actual Fuzz Face, this duty cycle change is severe and happens with the Fuzz control in most settings, as the waveform is squared off. There is also a relationship to the duty cycle modulation from my Chapter 19 Addendum on tube amps.
I do not have a published transfer function for this or a discrete answer for that homework problem. The main thing here is to look for a way to 1) clip the signal and 2) adjust the duty cycle which will clearly require a non-asymmetrical waveshaper function; note that it will also introduce a DC offset due to the duty cycle change (this is another part of the open-ended-ness of the question) and you can use a simple 1st order HPF with fc = 1Hz to eliminate the DC.
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