The Pedal Movie - for gadget makers or history bufs

The Pedal Movie (2020) is a 1:42 long documentary, reviewing the history of guitar pedals and examining the industry. IMDB Rating of 7.2

I edited these squeezed down temporay 5 min snippets to give you an idea of the content.

They do get into digital effects, noting the loss of something in some of the 80s combination boxes, also touch on DSPs. Discussions of the business include the many “Botique” brands build in garages.


Example Simple to use Audio DSP chip; the Analog Devices ADAU1701, long in the tooth and not that powerful by today’s standards, does include on a single chip 28-/56-Bit Audio Processor with Two ADCs and Four DACs. DSP programming can be a real challenge, Analog Devices has a visual programming language with a library of predefined functions. (The bare chips are sold on Amazon for $7)

El Rockero, a 2014 open source pedal project that apparently stalled over Sigma Studio code distribution concerns expressed here.

Comprehensive 10 year old CalPoly edu paper referencing the 1701
Electric Guitar Amplifier With Digital Effects

The newer more powerful chips don’t have integrated CODECs , the number of pins make them a more challenging PCB exercise.
This chip might be suitable for a clean moderate power single effect box, you can buy the chip preinstalled on a board , allowing one to perhaps put together a stand-along prototype with no surface mount PCB work.

. . . (DSP on bottom of PCB below)
DSP Board
These have been used in a number of earlier Audiophile room acoustics tuning setups.
The Sun/Wondom DSP board with breakout connectors (processor chip is on the bottom) This is usually paired with an RCA connector interface board for audiophiles, a pedal board would probably go another way. There are a number of sources that sell these “Wondom” branded PCB assemblies (Amazon/m Aliexpress. Ebay)

DSP Board stacked on RCA interface board, this board set,
ADAU1701 2 board set
(There may also be a programmer board involved)

Audiophile board sites using this chip.
The FreeDSP Project has 13 different Audiophile board designs
Blank and populated PCBs offered here.
An untested PCB Design
Hackable Article 2014
Audio dSP for diY applications paper

PedalPCB Site Mention
DIYstompbox Mentions
Program the DSP step-by-step video

Connect Guitar? . . . . . . Guitar Reverb? (only 43ms of RAM)
( Search Guitar Answers)

Texan instruments application powerpoint pdf for one of their DSP chips on an expensive? evaluation board.
Digital Guitar Effects Pedal
Shows simple model logic diagram for:

  • Distortion
  • Chorus
  • Reverb

I own that one. When I bought it, it was half that Price :astonished:

They are no USBi header to program the dsp on the board.

That chip has a Linux kernel driver but I couldn’t find any working device tree overlay for the RBPi or any other arm bases chip sbc.

I have to admit that I didn’t find thé time yet to investigate further …

In my casual research some years ago, I didn’t find any method to interface the internal ADC/DAC to an other device, interfaces seem to be just? boot source options.

How to Program Guide for a similar board.

This Arduino I2C interface lib consolidates the generated code into a simpler header,

a little samd21 board like a Pi Pico or tiny Adafruit QY Py with 2Mb flash pads, might make a sufficient UI connector in a little box project, hopefully can eliminate need fror programming board…

An Arduino Shield interface

That board looks like the ideal minimal guts for a pedal, Can you tell if your copy has the ADAU1401 or the ADAU1701 (turns out to not really matter)

(Just added El Rockero project reference above…)

Spec sheets were looking identical, found the FAQ Answer:
(1401 high higher temp range)

What is the difference between the ADAU1701, ADAU1702, and ADAU1401?

Functionally, these parts are identical. The differences are in the sizes of the program and data RAMs. The ADAU1701 has 1024 instructions/cycle in the program RAM and 2k words of data memory, while the ADAU1702 has 512 instructions/cycle and 0.5k words of data memory. The ADAU1401 has the same specs as the ADAU1701, but is qualified over the automotive temperature range.

I suspect there are a lot more of these embedded in amplifiers doing simple crossover filtering than in guitar pedals.