PedalScope 1.0 is on the Mac App Store
PedalScope measures what a guitar pedal does to a signal. You loop the pedal between your audio interface’s output and input, click once, and the app plays a test signal through it and records what comes back. The result is a set of charts that state what was measured, how far the measurement can be trusted, and where it stops being a measurement.
Six measurements
Together they make up a fingerprint:
- Transfer Curve. The clipping shape, drawn from the measured cycle.
- Harmonic Distortion. Each harmonic in dB across the neck, with the measurement floor drawn on the chart.
- Compression. Output against input level, with the knee where the fit puts it and a bound where the data cannot place it.
- Gain Map. Distortion across both frequency and level, so you can see a pedal clean up as the input falls.
- Chord IMD. The tones a pedal inserts between the notes of a played chord, ranked and named.
- Waveform Matrix. The captured waves themselves, quiet to loud, low to high.
Audio Unit plugins get the same treatment as hardware. A plugin is hosted outside the app and measured offline, and every record stores the plugin’s version and state. Measure a setting at two sample rates and compare: a plugin that oversamples properly reads the same at both.
Compare puts two records side by side and reports the gap as quantities: level, asymmetry and hardness, in dB. Every A/B in the app is matched to equal loudness, so nothing wins by being louder.
What is free
The download is free. Simulation Mode, the library, every chart, the rendered illustrations, the summaries, export and import are free and stay free. Measuring your own hardware and plugins is a one-time in-app unlock.
Simulation Mode is a complete virtual drive circuit: threshold, symmetry, knee, filters. You change a component and measure the result with the same six tools. It runs on a laptop with nothing plugged in.
What you need
An Apple silicon Mac running macOS 26 or later. For hardware measurement, an audio interface with a line output and a line or instrument input. Plugins and Simulation Mode need no interface.
Private by construction
Your measurements stay on your Mac. There is no account and no analytics. The App Store purchase is the only network use.
Measuring change over time
Every measurement in this version reads a pedal in a settled state, at a steady level. Measurements of how a pedal’s behavior changes over time are in development: how quickly it recovers after a loud burst, whether it responds differently coming down from a loud passage than going up to it, and how it follows a decaying note. They will arrive as a free update, covered by the Measurement Unlock.
Checked, and published
The measurements are checked against answers known before anything is plugged in. The project’s Reference Box holds six circuits whose distortion was computed from resistor arithmetic and Fourier theory before the box was built. One of them must produce a harmonic ratio of exactly −13.98 dB; PedalScope measures −14.0. The work behind that check is public:
- Two measurement libraries, free to download and open without a purchase: the Reference Box, 37 records, and eight overdrive and distortion pedals across four widely recognized commercial models, each measured with its drive at min, noon and max, 150 records.
- The methods documents: a technical reference and a plain-language companion, built from the app’s own measurement code, with a Python reimplementation of the analysis held to parity with the app.
- The hardware plans for the Reference Box and the Breakout Box that sits in the measurement loop beside it, as open hardware.
All of it lives in one public repository, PhaseDog/pedalscope-open-source, gathered on the Open Source page. The app itself is not open source.
Read more
The guide explains every chart. The Reading Room explains why each measurement matters to a musician. The FAQ answers the common questions.