When it comes to amp modeling and effect processing, we’re in a golden age for guitarists. The choices for gear are almost endless. Why do we need another?
Well, almost all of the available solutions are based on proprietary platforms. pi Stomp is open source software running on hardware that You built.
Being a more open and general purpose platform, you can hack or extend it by:
It certainly is more hackable and upgrade-able! Performance wise, it's very close in many regards, and even has some unique features. But in general, if you're not the DIY type, or if you want a pro quality product, please buy one those. Each was designed by a large team, in a well funded company, and assembled in a production factory.
pi Stomp is a hobbyist project For hobbyists. If you’ve always wanted to build your own multi-effects unit, here’s your chance. I put my blood sweat and tears into it, so you can have the same enjoyment I have when I plug in and make awesome sounds thru something that I built. If you’ve ever built your own effect or amp, you know what I mean. Now imagine an entire do-anything pedalboard that conforms to your crazy musical ideas!
The flip-side is that you will need to invest some time and effort. Although the wiring is similar or even simpler than many stomp boxes, the circuit board assembly is rather advanced. Please see Building pi Stomp before purchasing parts.
|pi-Stomp Core||pi Stomp v1 (superseded by pi-Stomp Core)||MOD Duo||HX Stomp||Headrush Gigaboard|
|Audio||24-bit 48kHz or 96kHz||24-bit 48kHz or 96kHz||24-bit 48kHz||24-bit 96kHz||24-bit 96kHz|
|Number of Plugins (FX, Models, etc.)||358+ (user upgrade-able)||358+ (user upgrade-able)||330+ (user upgrade-able)||200 (not upgrade-able)||107 (not upgrade-able)|
|Simultaneous Plugins||Typ 12+ (depends on CPU demand)||Typ 12+ (depends on CPU demand)||Typ 12+ (depends on CPU demand)||6||12?|
|Plugin Routing||Completely flexible||Completely flexible||Completely flexible||Serial or two parallel||Serial or two parallel|
|Plugin types||Effects, Models, Generators, Loopers||Effects, Models, Generators, Loopers||Effects, Models, Generators, Loopers||Effects, Models, Looper||Effects, Models, Looper|
|DIN (5-pin) MIDI||Optional In and/or Out||In||In & Out||In & Out/Thru||In & Out/Thru|
|USB MIDI||In & Out||In & Out||In & Out||None||None|
|Expression Pedal Input||Optional (up to 8 Analog controls)||Yes||No||Yes||Yes|
|Footswitches||Optional (up to 13)||3 (user assignable)||2 (user assignable)||3 (multiple modes)||4 (multiple modes)|
|True Bypass||Yes for Channel 1, Chan 2 always on||Yes (latching relays - save state when powered off)||Yes (mechanical relays)||Yes (mechanical relays)||Apparently Not|
|Audio Ins/Outs||2 in / 2 out (independent or stereo)||2 in / 2 out (independent or stereo)||2 in / 2 out (independent or stereo)||2 in / 2 out (stereo)||1 in / 2 out (stereo)|
|LCD||Color!||Monochromatic||2x Monochromatic||Color||Color / Touch|
|Can use as a USB audio interface||Not currently (OTG required)||Not currently (OTG required)||Yes||Yes||Yes|
|Wireless Connectivity||WiFi & Bluetooth||WiFi & Bluetooth||WiFi & Bluetooth||None||None|
|Software/Firmware||Open Source/Hackable/Upgrade-able||Open Source/Hackable/Upgrade-able||Open Source/Upgrade-able||Proprietary/Upgrade-able||Proprietary/Upgrade-able|
|Hardware||Very Hackable/Upgrade-able||Hackable/Upgrade-able||Proprietary/Expandable via port||Fixed Proprietary||Fixed Proprietary|
|Dimensions (in)||4 x 2.7 x 1.75 (w/o enclosure), 4.7 x 3.7 x 2.0 (smallest enclosure)||7.4 x 4.7 x 2.0||7.1 x 6.3 x 2.9||7.0 x 5.0 x 2.6||13.0 x 8.9 x 2.6|
|Cost||$159 (without enclosure or other options)||$198 (depends on sources)||$550||$650||$599|
Another product by the great folks at blokas.io named “pisound” (https://blokas.io/pisound/) is similar in core functionality to pi Stomp and MOD Duo. It's not listed in the table above because it lacks features which are generally desired for a stomp box form factor. Pisound has only one footswitch, no bypass, no tweak/expression controls, no LCD, and I/O jacks with rather low input impedance (100k ohm, quality guitar effects usually shoot for 10x that: 1Mohm). But, for a table based mutlti-effect unit, or if keyboards are more your game, it's worth checking out.
With 24-bit 96kHz I/O and a quad core 1.4 GHz processor, pi Stomp certainly has the processing power to rival the some of the best units. A vast number of current commercial recordings have been produced within computer systems with less power than pi Stomp. And remember, rendered CD quality is 16-bit 44.1kHz.
Where commercial multi-effects are likely to excel, is in the quality of the individual effect software models. Each included effect has a whole team of sound professionals committed to creating near perfect models of popular classic and novel amplifiers, cabinets and effects. The current pi Stomp software uses the LV2 open standard for coding of plugin effect models. There are over 400 available LV2 plugins out there. However, like with any community developed open software, the quality can range from awesome to unusable.
To get a sense of what LV2 plugins are capable of, check out the example pedalboards with sound samples on the Listen page.
The LV2 standard is relatively new and the audience is smaller than the similar Windows/MacOS based audio plugin formats (VST, AU, AAX, etc.). Some of those plugins may be able to be ported to LV2. But there are also some companies/organizations/individuals creating some awesome native LV2 plugins, like guitarix and CALF. As the community grows, so will the quality. You can even be part of that! Create your own plugin (Build & deploy a LV2 plugin ), add it to your pi Stomp, share it with the world!
Although pi Stomp! can replace a full pedalboard, it can also be used quite well with your other pedals chained before, after or within the fx-loop. So your personal tone can still leverage the pedals that you love and then use pi Stomp to add effects that you don't otherwise own, wish to consolidate or automate with presets, etc. One usecase, is to use it as a simple stomp box instead of a full pedalboard, providing less used effects (eg. pitch shifter, envelope follower, rotary speaker, etc.) as an alternative to cluttering your physical pedalboard with each of those.
To my knowledge, there are only two makers of HiDef Raspberry Pi audio cards that include inputs (ADC). Both work with pi-Stomp. Those and most DACs in fact, run on 3.3volt supplies allowing a maximum headroom of about 3 volts. That still exceeds 0dBu Pro ref level (2.19v) and 0dBV consumer ref level (2.828v) but is significantly lower than 9v. If you demand the headroom offered by a 9v or even 18v analog pedals, you might not like pi-Stomp. It may feel compressed or lacking in dynamics.
Now we get into some geekier details. Most commercial multi-effects units are DSP based. Their processing is purpose-built to process audio in a real-time operating system (RTOS). pi Stomp! being based around Raspberry Pi and Linux, a general-purpose operating system (GPOS), is at somewhat of a disadvantage because the CPU can be busy processing tasks that a DSP doesn't have to worry itself about. The Raspbian based OS used in pi Stomp! has been optimized to eliminate or reduce many of the potential distractions that might be encountered if the Raspberry Pi was being used as a “desktop” computer, but still, buffer overruns (aka Xrun's) can be encountered when the CPU is overwhelmed and that can result in audible anomalies (eg. glitches, pops, etc.) Given the power of the Raspberry Pi 3's quad cores, Xruns are typically infrequent unless you're running a pedalboard with many plugins, greater than 8 or 10 maybe, or if quite a few of the plugins are “simulators”. The bottom line is that there's more potential for audible glitches with a GPOS based processor. A glitch here and there is usually tolerable by most recreational musicians. If you're of the more professional variety, a commercial unit might suit you better.
Digital noise is also more likely in a GPOS based system because the CPU is constantly processing requests for its many services, passing data over its various interfaces (GPIO, Wifi, etc) and radio frequency noise is just rather prevalent on development boards like Raspberry Pi. The route of digital noise into the audio path is usually via inductive coupling. Shielding and physical distance are the typical solutions applied to reduce that coupling. Experiments with shielding were done but didn't seem to reduce coupled noise by any measurable amount. Instead, I chose to keep the audio portions of the system physically sequestered to one side of the board, away from the LCD backlight and Pi as much as possible. There will be some high frequency noise noticeable when the output is sent to an amp running at high volumes. In my opinion, it's not as annoying as the noise from many gain pedals or the common 60Hz hum, but it is there and something to consider if the highest of Fi is your grail.
Actual lab test results of pi-Stomp can be found here