Author Topic: Where to find DSP theory used in guitar pedals  (Read 513 times)

misnelstain5

Where to find DSP theory used in guitar pedals
« on: May 21, 2020, 09:30:17 AM »
Hello, all! I'm looking to homebrew some effects pedals for my electric guitar. Anyone know of any resources that explain the basic signal processing behind the pedals? For example, I know a wah is just an adjustable bandpass filter, delay just holds onto samples for a little bit before sending them out, or an octaver shifts the pitch an octave. Thanks in advance!

Digital Larry

Digital Larry
DSP tinkerer and former transistor twister

potul

Re: Where to find DSP theory used in guitar pedals
« Reply #2 on: May 22, 2020, 02:04:32 AM »
the DAFX book is a good reference for DSP oriented to audio.

You can peek the content in google books and already find interesting stuff in the preview pages. If you like it, you can always buy it.

https://books.google.es/books?id=DX-mRhkJL74C&pg

potul

Re: Where to find DSP theory used in guitar pedals
« Reply #3 on: May 22, 2020, 02:11:12 AM »
I found this interesting presentation with some good explanations and examples of code in MATLAB that can help you understand the concepts:

http://users.cs.cf.ac.uk/Dave.Marshall/CM0268/PDF/10_CM0268_Audio_FX.pdf

And if you go one step above the folder, you will find more basic dsp stuff that can be helpful

http://users.cs.cf.ac.uk/Dave.Marshall/CM0268/PDF/
« Last Edit: May 22, 2020, 02:16:26 AM by potul »

Digital Larry

Re: Where to find DSP theory used in guitar pedals
« Reply #4 on: May 22, 2020, 02:55:28 AM »
Julius O. Smith is a leader in this area.

https://ccrma.stanford.edu/~jos/pasp/pasp.html
Digital Larry
DSP tinkerer and former transistor twister

Firesledge

Re: Where to find DSP theory used in guitar pedals
« Reply #5 on: May 22, 2020, 08:03:05 AM »
Documentation about circuit simulation and “analogue” filter design:

The Art of VA Filter Design
A very good book with all you need to know to create analogue-like filters. Warning: you’ll have to somehow unlearn things about classical filter design (s-plane prototypes and BLT)

Andrew Simper’s technical papers
About filters designed with trapezoidal integration (description and pseudo-code)

Qucs technical papers here and here
Resources about Modified Nodal Analysis (MNA), numerical integration, convergence and everything you need to know to build a basic circuit simulator. This is for more complex circuits, when manually solving tons of equations is impractical.

A paper and a thesis with long titles
Once you’re comfortable with the MNA, you can switch to the Nodal DK method and its derivatives, which are more suitable for real-time use.

KVR 1, KVR 2
Some interesting tips and techniques in these threads.

And of course the DAFX archive, a mine of information on various related topics.
« Last Edit: May 22, 2020, 08:05:48 AM by Firesledge »
Pédale Vite, multi-FX pedalboard

micromegas

Re: Where to find DSP theory used in guitar pedals
« Reply #6 on: May 22, 2020, 08:04:28 AM »
This book is also quite nice and explanatory, and even comes with some basic C++ examples: https://www.oreilly.com/library/view/audio-effects/9781466560284/

I may be biased because both authors are professors at my University (one of them was my MSc supervisor and the other is now my PhD supervisor), but the book is a good source of info.

The DAFx book is more detailed in many aspects and definitely something to have at hand as a reference.

Will Pirkle's book has some nice implementation tips: http://www.amazon.com/Designing-Audio-Effect-Plug-Ins-Processing/dp/0240825152/ref=sr_1_2?ie=UTF8&qid=1350140462&sr=8-2&keywords=will+pirkle

JOS books are gold too. This one in particular encompasses much of the theory that goes into many of the DSP based audio effects that designers do use: https://ccrma.stanford.edu/~jos/pasp/. It may be math heavy if that's something you are not looking to get into.

Also, for more specific stuff, do check conference proceedings (for example DAFx and AES) is not just academics there, but also engineers from really high-profile companies from time to time..
Software Developer @ bela.io

potul

Re: Where to find DSP theory used in guitar pedals
« Reply #7 on: May 22, 2020, 09:15:50 AM »
OMG, I didn't know the DAFX archive... this is really a mine for information.

Thanks for the link!