Stompbox 2013

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Stompbox Design Workshop

CCRMA Summer Workshop 2013
August 19-23

Instructors: Edgar Berdahl and Esteban Maestre esteban@ccrma.Stanford.EDU



Come design your own flavor of stompbox at Stanford Universityʼs Stompbox Design workshop. We will teach you a brand new platform for implementing stompboxes that not only enables you to create any sound effects from the past but also promotes the creation of new sound effects. Our resources for new media design are also at your fingertips if you would like to re-design the concept of a guitar stompbox: for example, put a Wiimote on your guitar and use it to change the sound of the effect, or use some LEDs to simulate the glow of vacuum tubes, or even incorporate a micro-sized Pico projector into your stompbox! The expanded world of digital audio effects is at your fingertips because the workshop incorporates:

  • Most basic theory of signal processing
  • Description of operation of prior stompboxes and digital audio effects
  • Laboratory exercise teaching you how to program our own open-source software and hardware platform involving:
    • connecting to your stompbox over an Ethernet connection from your laptop
    • creating new digital audio effects by connecting together basic building blocks in the graphical
    • programming language Pure Data
    • building simple button and knob interfaces to Pure Data
  • Introduction to human-computer interface devices for projects

Further discussion of open-source hardware and software platforms including Satellite CCRMA. Finally, we will round out the workshop with a roundtable presentation of the stompboxes you create followed by an optional evening jam session for fun.

The primary programming language to be used during this workshop is Pure Data. Besides C++ digital audio effects programming (a somehow more classical approach), a programming language becoming more and more popular for signal processing (being lower level and at first less intuitive than Pure Data) is Faust [1], but it will be left out of support for the basic lab exercises. Depending on the interest of participants, Edgar may briefly lecture about the basics on Faust programming so that you can get an idea. Of course, you are very welcome to satisfy you curiosity. An excellent tutorial for audio signal processing in Faust written by Prof. Julius Smith can be found here [2].

This workshop is intended for musicians interested in exploring new possibilities in digital audio effects in a hands-on and technical way; Makers, engineers, computer scientists, or product designers interested in exploring artistic outlets for their talents and collaborating with musicians; and/or anyone looking to gain valuable skills in basic audio signal processing and human-computer interfaces, with a focus on invention. Participants are encouraged (but by no means required) to bring their own laptop computers and/or musical instruments.

This workshop was created by Edgar Berdahl and Esteban Maestre in 2011. This workshop uses very similar hardware to the New Music Controllers workshop, but the focus is more on applications to stompbox design and audio signal processing.

How to sign up for the workshop.


We will meet from 9am-5:00pm daily, with mini-breaks at around 10:30am and 3:00pm, and a lunch break aproximately between 12:00pm and 1:00pm.

The Week
Date Morning (9am-12noon) Afternoon (1:00pm-5:00pm)
Monday Introduction, Overview, Pd basics lecture (incl. one digital effect example), Kit How-To, Lab 0: Making Sound with Satellite CCRMA Review Lab 0, FX Lectures 1 and 2, Lab 1: Making FX In Pd
Tuesday Review Lab 1, FX Lecture 3, Introduction to Electronics--Sensors1 Lab 2: Controlling an Effect with Real Sensors
Wednesday Lab 2 Review, Interfacing With The Rest Of The World (i.e. making cables, etc.) FX Lecture 4, Optional guided laboratory time or start on project
Thursday FX Lecture 5, Refine project ideas, Work on project, Enclosure How-To Work on project
Friday Work on project Project presentations (3:00pm - 4:30pm)


In this section we provide links to the FX Basics lectures we'll go through during the week, and complementary materials. Because of the limited time we have for this workshop as compared to the vast amount of theory and literature behind digital audio effects and their implementation via different programming languages, the contents of these lectures are limited to introducing the very basics of some of the most popular types of audio effects used in stompboxes. For a deeper coverage of signal processing techniques behind digital audio effects, please refer to the CCRMA courses listed below (in the References section) and their complementary materials or books.


FX Introductory lectures:

Fx Basics 1: Introduction

Fx Basics 2: Dynamics Effects

Basic PureData demo patches:


Tremolo (here without graphical signal displays)

Noise gate (here without graphical signal displays)

Compressor (here without graphical signal displays)

Bear in mind that these Pure Data patches were created to illustrate the basic principles of some elementary digital audio effects. For that purpose, some graphical displays were added as a visual complement to monitor some (control) signals. Remember that, although potentially useful for debugging/monitoring purposes, those graphical displays (i.e. the [table] objects) do not contribute to sound processing. However, they may cause the Raspberry Pi to run very slow, so it's good to remove them (together with the corresponding [tabwrite~] objects), or use the alternative patches not including graphical signal displays!

Lab resources:

Categorized list of Pd Objects (on a single page here)

Ugly guitar track 'solo_man.wav'

More guitar/bass tracks (compressed ZIP)

Nicer guitar tracks Courtesy of Jonathan Abel, please do not distribute.


FX Introductory lecture:

Fx Basics 3: Filtering

Basic PureData demo patches:

Biquad block example (here without graphical displays)

Wah example using a 2nd order peaking filter (here without graphical displays)

Lab resources: Basic Pd filtering library by Mike Moser-Booth - Latest version (not checked) of the above library can be found at .


FX Introductory lecture:

Fx Basics 4: Distortion

Basic PureData demo patch:

Distortion / Fuzz (here without graphical displays)


FX Introductory lecture:

Fx Basics 5: Time Effects

Basic PureData demo patches:

Simple delay

Simple tapped delay

Feedback Delay



(No lectures on Friday)


One of the goals of this workshop is to help you get hands-on experience building a novel stompbox project of your choosing. You are encouraged to work with other workshop participants on the project, particularly those who might have skills that complement your own. Since the workshop is short, it is a good idea to start thinking of ideas during the first lectures and labs; during the second half of the workshop, you will primarily be working on getting a "demo-able" prototype ready for the project presentations on Friday afternoon.

Here is the template we used to laser-cut the enclosure parts you'll be using for the raspBerryPI. These could be modified to meet your own needs/taste, so they can be sent to cut by Ponoko.



(see links in course schedule)


  • The lectures will primarily be in Pure Data (Pd) Extended for sound synthesis. We will introduce some other alternatives such as writing plug-ins directly in C/C++ or with Faust.
  • The micro SDHC card for your kit will be initialized with Satellite CCRMA so that you can get up and running instantly.
  • The Raspberry Pi platform enables linux to run on a high-power 700MHz CPU. It can execute floating point operations natively, which is essential for rapid prototyping of audio algorithms.
  • The Arduino software could be used to change the Firmata-based firmware that gets data from the Arduino Nano board into Pd.




Project questions

  • Can I do ____ for my project?

You can do whatever you would like for your project. Keep in mind that you really only have a few days to work on it, so you might want to focus on one crucial aspect of a larger project that you'd like to have working.

  • Can I incorporate my own hardware and software into my project?

Yes, you can, although we have limited time and ability to support hardware and software other than what is introduced in the labs.

  • Can I keep the tools we use during the workshop?

If you buy the kit!

StompboxFlyer 2013 small.jpg