10 DIY Digital Stompbox / Effect Pedal Platforms Review

Figure 1. DIY Stompbox / Effect Pedal (Google Image Search)

To start researching on DIY (do-it-yourself) digital  stomp box / effect pedal for the next project, let’s take a look at some popular platforms to compare their specifications and prices.  Here some of them in my list:

  1. Electrosmash’s pedalSHIELD UNO
  2. Electrosmash’s pedalSHIELD MEGA
  3. Electrosmash’s pedalSHIELD DUE
  4. Electrosmash’s Pedal Pi
  5. Openmusiclabs’s Stomp Shield
  6. Hoxton OWL
  7. Teensy
  8. Axoloti
  9. SlackDSP
  10. Sparkfun’s Proto Pedal

Electrosmash’s pedalSHIELD UNO

This stomp box platform is based on Arduino UNO, employing its 10-bit ADC for the audio input and two 8-bit PWM for producing 16-bit output. The output stage includes a low-pass filter at 5 KHz cut-off frequency using a second order of active filter (with op-amp). The arduino UNO runs is a 8 bit AVR microcontroller runs on 16MHz clock, and with only 2KB of RAM there would be very small space for delay-line based effect. With such low frequency cut-off of the output, we can say that this pedal could only produce a low-fidelity. The total price to build the complete working stomp box using this platform is the price of the shield kit (39 USD) plus the Arduino UNO (22 USD) or 61 USD.

Electrosmash’s pedalSHIELD MEGA

The pedalSHIELD MEGA is similar to the pedalSHIEL UNO, but it employs Arduino MEGA as its core. The RAM capacity is 8KB, and it has OLED display for better control visualization. The input and output stages is the same with UNO version, so the sound quality would be similar. The total price to build a working stomp box will be the price of the shield board (59 USD) plus the Arduino MEGA board (38 USD) or  97 USD.

Electrosmash’s pedalSHIELD DUE

This pedal shield model is the most advanced platform from Electrosmash that employs Arduino board as its core, because of the powerful core of the Arduino DUE. This pedal has three programmable potentiometer for the parameter controls, a mix switch, and a programmable switch. The Arduino DUE has 32 bit SAM3X8E ARM Cortex M3 microcontroller running at 84 MHz, with 96KB of RAM  and 512 KB of Flash memory. The input and output conversion is better than the previous Arduino based shields but unfortunately it employs only the built in 12-bit ADC and DAC, so it would still be considered as low fidelity output. It uses double channel for both ADC and DAC to increase the reading range, but in my humble opinion it would be useless in terms of increasing the resolution since the reading of both channel of the ADC or the writing of both channel of DAC will result in the same bit changes, nothing more than doubling the single channel reading or writing. It should have powerful computation resource for implementing many type of digital effect, but unfortunately the output resolution would be only 12-bit (please correct me if I’m wrong in deducting its final resolution). The price to build the complete stomp box will be around 53 USD for the shield plus 40 USD for the Arduino DUE, or 93 USD in total.

Electrosmash Pedal-Pi

The most powerful stomp box platform from Eelectrosmash should be Pedal-Pi, but it’s really-really unfortunate that it has only 12-bit A/D converter. Using pi-zero board as the core, it has very powerful 1 GHz ARM11 core with 512MB of LPDDR2 SDRAM. The booting time for Linux operating system might be unsuitable for live performance when it need fast restart from power failure, but it might be fine for studio recording if it has at least 16-bit codec for input-output conversion. The cost to build this stomp box will be 65 USD for the shield and 5 USD for the Pi-Zero, or 70 USD in total cost for 1 GHz processing core!  This is an incredible processing power  for very low cost but sorry to say,  the low fidelity of 12-bit audio conversion make the power of Pi-Zero useless in generating high fidelity audio output.

Openmusiclabs’s Stomp Shield

Stomp Shield is an Arduino shield from openmusiclabs (dot com), works with Arduino Uno and Duemilanove. It has analog level control for input and output, analog feedback that feed the 16-bit (from double 8-bit PWM) output of the Arduino back to its analog input. It also has analog mix control that adjust the proportion between the original signal and the processed signal that is mixed to produce the final output. The digital control is done through a rotary encoder, but unfortunately there is no display to show any operation modes or states. The input conversion is done by the Arduino analog input, which has only 10-bit resolution. To build this stompbox, the total price would be around 91 USD (69 USD for the shield plus 22 USD fro the Arduino UNO).

Hoxton OWL

This pedal is sold in completely built unit, but as being open source, the schematic diagram of the hardware and the source code of the software are available. The hardware specification can be considered as high-end, as shown in the list below:

  • Powerful microcontroller:
    • 168MHz 32bit ARM Cortex M4
    • 192KB RAM, 1MB Flash memory
    • Integrated DSP, FPU, DMA
  • 8kHz to 96kHz sampling rate
  • More than 3000 instructions per sample @ 48kHz
  • 1MB external SRAM
  • 16/24 bit codec
  • Stereo in/out
  • USB MIDI
  • 4 assignable control knobs
  • Bypass foot switch
  • Expression pedal jack
  • Assignable illuminated pushbutton

Looking at the specification, this pedal should be capable of implementing high-end effects such as vocal-guitar harmonizer or vocoder. This pedal is sold 239 GBP or about 323 USD (at the time of writing this article), and it would be great option if you have a priceless unique effect model that you have in your mind that  is not available on the high-end effect market, so you have to code yourself for this pedal.

Teensy

(to be continued)