Here are some links to information on guitar effects:

Most DISTORTED Guitar Tone Possible?!
https://www.youtube.com/watch?v=TkO-yau7jdQ

What does distortion look like?
https://www.youtube.com/watch?v=pFSX93aPzmw

Understanding Distortion (Pt2) – Diode Clipping circuits
https://www.youtube.com/watch?v=6Qs1H2qTAWI

Demonstration of Overdrive, Distortion and Fuzz effects on oscilloscope and with a guitar signal
https://www.youtube.com/watch?v=8NjeHHroOgI

The World’s Largest Guitar Pedalboard (world record)
https://www.youtube.com/watch?v=iWRfLuJ_NKw

She sings through guitar pedals and it sounds AMAZING
https://www.youtube.com/watch?v=77iUH208XaI

Modeling A Guitar For Circuit Simulation
https://hackaday.com/2023/08/19/modeling-a-guitar-for-circuit-simulation/

Guitar effects have come a long way from the jangly, unaltered sounds of the 1950s when rock and roll started picking up steam. Starting in large part with [Jimi Hendrix] in the 60s, the number of available effects available to guitarists snowballed in the following decades step-by-step with the burgeoning electronics industry. Now, there are tons of effects, from simple analog devices that would have been familiar to [Hendrix] to complex, far-reaching, digital effects available to anyone with a computer. Another thing available to modern guitarists is the ability to model these effects and guitars in circuit simulators, as [Iain] does.

[Ian] plays a Fender Stratocaster, but in order to build effects pedals and amplifiers for it with the exact desired sound, he needed a way to model its equivalent circuit. For a simple DC circuit, this isn’t too difficult since it just requires measuring the resistance, capacitance, and inductance of the overall circuit and can be done with something as simple as a multimeter. But for something with the wide frequency range of a guitar, a little bit more effort needs to go into creating an accurate model. [Iain] is using an Analog Discovery as a vector network analyzer to get all of the raw data he needs for the model before moving on to some in-depth calculations.

Guitar Pickup Equivalent Circuits
https://macalisterelectronics.com/guitar-pickup-equivalent-circuits.html

An equivalent circuit of a guitar’s pickups, tone/volume controls and cable is useful when designing input stages for effects pedals or amplifiers. It makes simulations or calculations of how input networks modify the spectrum of the guitar’s output more realistic. This article covers some background on the topic and then goes into a technique for measuring the output impedance of a guitar and how to deduce the values of an equivalent circuit from the measurement. The equivalent circuit of a Stratocaster are given in the Conclusion at the end of this page.

Sebastian of Baltic Lab demonstrates how to implement overdrive and distortion effect DSP algorithms on the Arduino GIGA R1 WiFi
https://baltic-lab.com/2023/08/dsp-diode-clipping-algorithm-for-overdrive-and-distortion-effects/

Open Source Analog Effects Pedal
A modular platform for developing and trading guitar (and other) audio effects. Focus on, but not limited to, pure analog signal path.
https://hackaday.io/project/2311-open-source-analog-effects-pedal

Guitar Distortion With Diodes In Code, Not Hardware
https://hackaday.com/2023/08/23/guitar-distortion-with-diodes-in-code-not-hardware/

Guitarists will do just about anything to get just the right sound out of their setup, including purposely introducing all manner of distortion into the signal. It seems counter-intuitive, but it works, at least when it’s done right. But what exactly is going on with the signal? And is there a way to simulate it? Of course there is, and all it takes is a little math and some Arduino code.
https://baltic-lab.com/2023/08/dsp-diode-clipping-algorithm-for-overdrive-and-distortion-effects/

Guitar Effects With No (Unwanted) Delay
https://hackaday.com/2021/03/15/guitar-effects-with-no-unwanted-delay/

Raspberry Pi Pico – Guitar To MIDI
https://www.youtube.com/watch?v=Fu0Qsz2h3HE

This story of history of computer music starts from 1951 when the first computer music recording was made using a Ferranti Mark 1 computer at the University of Manchester. That computer played God Save The Queen, Baa Baa Black Sheep and In The Mood. The revolution had begun… Lots of great development work was done in the 1960s and 70s.

Synthesizers were adopted by electronic acts and pop and rock groups in the 1960s and 1970s and were widely used in 1980s music. Sampling, introduced with the Fairlight synthesizer in 1979, has influenced all genres of music and had a major influence on the development of electronic and hip hop music. The Fairlight CMI (short for Computer Musical Instrument) is a digital synthesizer, sampler, and digital audio workstation introduced in 1979 by Fairlight. It was one of the earliest music workstations with an embedded sampler and is credited for coining the term sampling in music. It rose to prominence in the early 1980s. It was a very expensive equipment that was used by some of the big name artists and biggest studios. The song Running Up That Hill written and produced by Kate Bush was one of the first big hits that used Fairlight in the center of song making.

Kate Bush – Running Up That Hill (A Deal with God)

Commodore release Commodore 64 computer in 1982. The C64 that home computer music making really got going. It was notable for the inclusion of its SID sound chip, which enabled users to create music using a whopping three channels of synthesis. In fact, the distinctive SID sound is still popular today, which is one of the reasons why you can download C64 emulators for your Mac or PC.

The introduction of MIDI in 1983 was of crucial importance to high-tech music makers. This new protocol enabled computers, synths and other hardware to talk to each other, and is still in widespread use today. Without MIDI, computer music history would be very different indeed. Back in the 80s, the Atari ST (released 1985) was the machine that every computer musician wanted to own because it had built-in MIDI ports.

Commodore Amiga was a home computer family manufactured from 1985 to 1994. Amiga had very good sound chip for the time, the Paula sound chip could play back four channels of digital sampled sound at 8 bit resolution and 28 kHz sample rate. The Amiga was transformational due to its four-channel stereo sound. It was revolutionary for music makers. There were audio sampler/digitizer add-ons that allowed to record sounds to the computer. Those Amiga parallel port sound samplers were quite simple hardware devices from the late 80s/early 90s which allowed users to digitally record audio to their home computer.

Amiga Samplers: Budget dance music in 1990

There were a lot of Amiga music software. Starting from 1987 with the release of Soundtracker, trackers became a new type of music programs which spawned the mod (module) audio file standard. The Mod audio standard is considered the audio format that started it all in the world of computer music. After Soundtracker many clones (which often were reverse engineered and improved) appeared (like ProTracker in 1990). Those tools allowed to make a dance track on a budget home computer. With the reasonably priced home computer, some cheap extra hardware and some software you had basically in many ways better tools available than what was considered the very expensive “high end” less than 10 years ago.

It was the poor man’s studio. In the period from 1985 to 1995 the Amiga audio (which was standard in Amiga computers) was of greater quality than other standard home computers. From the second half of the 1990s, the most popular genres of tracker music have been electronic music genres such as techno, trance, hardcore and chiptune. There has been many competitions on computer demo party events where different music makers competed who makes best tracker music. I did not make music with tracker myself, but I have been involved in making some of those competitions on those events to happen (between years 1996-2004).

The tracker programs were instrumental in popularizing the MOD file format also on platforms other than the Amiga. The popularity of the file format led to the appearance of programs that reproduce it also for IBM PC. The problem on IBM PC in the late 1980′s and early 1990′s was lack of good sound output. Due to the variability and rudimentary nature of the PC’s sound equipment, the implementation of just the mod playing routine was significantly more difficult and posed a challenge to the programmers. However, the early PC demo groups wanted to show that the PC could do the same as the Amiga.

I did at the late 1980′s and early 1990′s some hardware and software development to improve PC sound features (before the sound cards became widely available). I developed software technology that allowed the PC internal speaker (that was originally designed make only simple BEEP sounds) to play back music samples. I have written my work on that My PC speaker PWM story post. My pretty much state of the art code was even integrated into Drum Blaster software from EPIC Megagames (but was never released out by some US patent issues that were not worth to fight in court).

I did design also hardware that allowed the PC printer port to be used for sound playback and even sound recording. In the late 1980′s PC sound was poor. One hack those days was the original Covox Speech Thing, that connected a simple DAC to to PC parallel port. The Covox Speech Thing was an external audio device attached to the computer to output digital sound. It allowed to play back sounds in considerably better quality than with PC speaker. That Covox thing was connected to PC parallel port, and it could work quite nicely together with the printer. The circuit was marketed around 1986 by Covox, Inc of Eugene, Oregon, for about 70 USD with the accompanying software (that included speech synthesis). This hardware was eventually supported by the old DOS games from Sierra and Id. I came by one device and it’s software one day around 1988 or early 1989. I did some thinking and analyzing, and came out with my own circuit simple design that worked same way as the original hardware but was easy to build by DIY electronics experimenters.

I posted the circuit to one BBS some day 1989, and the idea started to spread quickly. Immediately someone posted this circuit to some Finnish national BBS network. The plans spread well, file was very much loaded. It went viral. Very many people started building this circuit, and started spreading the software that uses it, first pirated version of original Covox software and later software developed by users. Soon several PC MOD music playback software and tracker software started to support it. It was a huge hit. Other people also designed improved versions of it, and I also made my own improved designs (based on R2R network, read DAC IC, added several different low pass filters to output to get rid of high frequency noise etc..).

Using a 1986 Covox Speech Thing clone on a modern machine in 2017

In addition to that parallel port DAC I pretty soon designed also my own parallel port sampler for PC. It was a 8 bit ADC chip that I interfaced to the PC parallel port. I used the bidirectional communications feature supported by some PC parallel ports (but not all) to get the 8 bit data nicely to the PC. So my design worked quite well on my PC, and some other PCs, but not guaranteed to work on other (even risks damaging some PC hardware). Due those risks I did not distribute my design widely in the early 1990′s. I had also plans for some more complicated better quality sound playback and recording devices, but the era of commercial sound cards had started… it did not seem to be worth anymore to design your own designs from scratch and waiting to get some software support for it.

In the 1990s PC computers at last started to become audio playback and recording devices in their own right. The very first of Creative Labs’ hugely successful Sound Blaster soundcard was launched in 1989 and Sound Blaster Pro soundcard in 1991.. Sound Blaster had capability to record and play back digitized sounds and also had musical synthetizer chip in it (Yamaha YM3812 / OPL2 that was used in Adlib sound card released few years earlier). The first Sound Blaster had only 8 bit recording. The launch of the Sound Blaster 16 in 1992 added 16-bit recording, which enabled the home computer user to record at ‘CD quality’. I started my PC sound card era with Sound Blaster card, and i pretty much ended designing my own sound hardware. It took many years until the sound card became the standard feature expected to be on PCs.

The PC demo scene favored the Gravis Ultrasound sound card, which, like the Amiga, played samples without consuming processor time. I got one for me, and it was truly amazing at the time. Many demo groups developed their own tracker. The two strongest PC trackers of the mid-1990s were the Finnish Future Crew’s Scream Tracker 3 and the Swedish Triton’s Fast Tracker II (which was the first to support 16-bit samples taken at a frequency of 44 kHz).

I continued experimenting with PC sound cards. I did some early PC sound card audio quality testing and published result on my web pages for several sound cards. That lead me later to take part in making one of the first PC sound quality measurement standard “Personal Computer Audio Quality Measurements 1.00″ started by Cirrus Logic in the later 1990′s. I contributed to standard and reviewed the technical material. Quality levels for some of these measurements are suggested in Microsoft’s PC ‘97, PC ’98, PC ‘99, Intel’s AC ‘97, and in the MPC3 specification.

When years got on, the sound became standard feature to the PC motherboards and laptops. Over the years AC’97 standard features integrated to PC motherboards made using external sound card not necessary for most users. The built-in sound hardware was typically quite simple 16 bit ADC and DAC hardware that played back sounds generated by software running on the main CPU. The PC CPU power had increased so much (higher clock frequency and multimedia signal processing commands) that quite complicated sound processing could be performed by the CPU only (not necessarily need for special synth and/or signal processing hardware built to sound card itself needed). Later Intel_High_Definition_Audio replaced AC’97.

Sources and links to more information:

https://www.epanorama.net/newepa/2018/01/18/covox-speech-thing-30-years-later/

https://www.epanorama.net/newepa/2014/09/29/my-lpt-dac-story/

https://www.epanorama.net/newepa/2014/10/02/my-pc-speaker-pwm-story/

https://fi.wikipedia.org/wiki/ProTracker

https://fi.wikipedia.org/wiki/Tracker-musiikki

https://www.readkong.com/page/personal-computer-audio-quality-measurements-2641069

https://www.thomann.de/blog/en/history-of-the-synthesizer/

https://artsandculture.google.com/story/https://www.synthhistory.com/

https://recoverit.wondershare.com/audio-recovery/what-is-mod-file.html

https://www.lemonamiga.com/links/index.php?genre=9

https://www.classicdosgames.com/game/Drum_Blaster.html

https://archive.org/details/DrumBlaster

https://archive.org/details/HDBLAST

https://www.youtube.com/watch?v=EbjThqAUvwg

https://cdm.link/2018/04/90s-alive-free-modern-clone-fasttracker-ii/

https://musictech.com/guides/essential-guide/history-of-trackers/

https://en.wikipedia.org/wiki/FastTracker_2

https://en.wikipedia.org/wiki/Sampler_(musical_instrument)

https://www.musicradar.com/news/4-iconic-samplers

https://www.thomann.de/blog/en/a-brief-history-of-sampling/

https://www.bandinabox.com/

https://www.pgmusic.com/

https://www.musicradar.com/news/tech/a-brief-history-of-computer-music-177299

https://en.wikipedia.org/wiki/Synthesizer

https://en.wikipedia.org/wiki/Fairlight_CMI

https://fi.wikipedia.org/wiki/Amiga

https://en.wikipedia.org/wiki/Amiga_music_software

https://www.theguardian.com/music/2022/may/02/poor-man-studio-amiga-computers-modern-music-jungle-calvin-harris

https://github.com/echolevel/open-amiga-sampler

https://hackaday.com/2020/08/08/an-amiga-sampler-30-years-later/

https://fi.wikipedia.org/wiki/AdLib

https://fi.wikipedia.org/wiki/Intel_High Definition Audio

https://fi.wikipedia.org/wiki/AC%E2%80%9997

Neural DSP is developing technology to advance the state of the art in the music industry – mainly effect plug-ins and DSP software and Quad Cortex DSP guitar effect box. Darkglass Electronics concentrates on making effect box hardware. Neural DSP has fast become a household name on the new frontier of amp modelling and guitar effects.

Neural DSP Quad Cortex is a pro-quality amp modeller and effects unit that presents its many features in an easy-to-use format. The Quad Cortex, is a floor-based unit that presses all that next-gen algorithmic sorcery into service in an anodised aluminium unibody. The Quad Cortex features a bright seven-inch LED touch-screen that allows you to adjust parameters and arrange signal chain. User can adjust the sounds and access all the functions from the touch-screen and the stomp+rotary actuators.

The Quad Cortex derives 2GHz of DSP power from SHARC+ processors that gives it its name, and this puts a lot of sounds on the menu. Quad Cortex may be the most powerful floor modeler on the planet with a total of 6 cores (4x SHARC+ and 2x ARM Cortex-A5 running at 500MHz each).

Here are some pictures I took at Knotfest Finland 2022 festival on the guitar effect setup Slipknot uses (from Slipknot museum featuring Fender Jim Root Jazzmaster):

Here is one video I found from YouTube related to Slipknot and Neural DSP Quad Cortex:

SlipKnoT – Surfacing | Bass Cover | Neural DSP Quad Cortex test

Sources and links to more information:
https://neuraldsp.com/
https://www.darkglass.com/
https://neuraldsp.com/plugins
https://neuraldsp.com/quad-cortex
https://www.musicradar.com/reviews/neural-dsp-quad-cortex
https://soundtools.fi/verkkokauppa/neural-dsp-quad-cortex-efektiprosessori-ja-vahvistin/
https://www.reddit.com/r/Guitar/comments/s5a2a2/play_tried_the_neural_dsp_archetype_petrucci/
https://kaaoszine.fi/mika-yhdistaa-foo-fightersia-slipknotia-ja-wintersunia-suomalaiset-darkglass-electronics-ja-neural-dsp-vievat-huippumodernia-soitintekniikkaa-maailmalle/