Further reading & credits
PedalScope’s measurements are implementations of published research —
none of the science here is ours. This page credits the ideas and points
the curious at the sources. (The authoritative attribution record, with
implementation and licensing notes, is ATTRIBUTION.md in the project
repository; the citations below are the same list, written for reading.)
Credits — the ideas inside the app
The swept-sine measurement. The trick that powers the Harmonic Distortion measurement — playing one exponential sweep and unpicking each harmonic from the response — is Angelo Farina’s swept-sine technique, refined by Antonín Novák and colleagues into the synchronized swept sine, whose phase alignment makes the harmonic responses usable individually:
A. Farina, “Simultaneous Measurement of Impulse Response and Distortion With a Swept-Sine Technique,” AES 108th Convention, 2000.
A. Novák, P. Lotton, L. Simon, “Synchronized Swept-Sine: Theory, Application, and Implementation,” Journal of the Audio Engineering Society 63(10), 2015.
A. Novák, L. Simon, F. Kadlec, P. Lotton, “Nonlinear System Identification Using Exponential Swept-Sine Signal,” IEEE Transactions on Instrumentation and Measurement, 2010.
The playable models. When a Hear-it panel plays “your pedal”, it is rendering through a generalized Hammerstein model — parallel power branches fitted from the measured harmonics, per the same Novák group:
A. Novák et al., “Analysis, Synthesis, and Classification of Nonlinear Systems Using Synchronized Swept-Sine Method for Audio Effects,” EURASIP Journal on Advances in Signal Processing, 2010.
Loudness matching. Every comparison is matched with the broadcast loudness standard (the reason is the louder-sounds-better bias):
ITU-R BS.1770-4 / EBU R128 (K-weighting, gated integration).
B. De Man, “Evaluation of Implementations of the EBU R128 Loudness Measurement,” AES 137th Convention, 2014 — the arbitrary-sample-rate filter parameterization the app uses.
The plucked strings. The illustration notes are extended Karplus–Strong synthesis — a pluck-shaped excitation circulating in a tuned, damped delay line, voiced here as a DI electric guitar (two weakly-detuned string polarizations into a pickup-position comb):
K. Karplus, A. Strong, “Digital Synthesis of Plucked-String and Drum Timbres,” Computer Music Journal 7(2), 1983.
D. Jaffe, J. Smith, “Extensions of the Karplus–Strong Plucked-String Algorithm,” Computer Music Journal 7(2), 1983.
Two-tone protocols. The chord roughness measurement descends from the SMPTE and CCIF/ITU-R twin-tone intermodulation conventions, re-cast as a musical interval on an analysis lattice that keeps every product’s label honest; the guitar-adapted forms of the two standards themselves were retired before 1.0 (see that page’s Modes section).
The perceptual words. When a summary says “brighter” or “smoother”, the underlying numbers are proxy implementations (openly simplified — see the honesty note on that page) of published psychoacoustic models:
E. Zwicker, E. Terhardt, “Analytical expressions for critical-band rate and critical bandwidth as a function of frequency,” Journal of the Acoustical Society of America 68(5), 1980.
DIN 45692:2009 (sharpness); H. Fastl, E. Zwicker, Psychoacoustics: Facts and Models, 3rd ed., Springer, 2007 (roughness).
Filters. Simulated-pedal tone stacks use Robert Bristow-Johnson’s “Audio EQ Cookbook” biquad formulas — the quiet workhorse of practically all digital audio EQ.
Independent cross-checking. The app’s analysis is validated against
Stefan Gündert’s independent syncsweptsine Python implementation
(github.com/SiggiGue/syncsweptsine) — at arm’s length, no code shared —
with agreement to within thousandths of a dB on reference nonlinearities.
Further reading
If this app made the subject interesting, these reward the time:
Novák’s swept-sine pages (ant-novak.com/pages/sss/) — interactive explanations of the method by its principal author.
Fastl & Zwicker, Psychoacoustics: Facts and Models — the standard text on why things sound the way they do: loudness, roughness, sharpness, masking.
Oppenheim & Schafer, Discrete-Time Signal Processing — the foundations under every DSP claim this guide makes.
The Audio EQ Cookbook (search “RBJ audio EQ cookbook”) — one page of formulas behind decades of digital tone controls.
Electrosmash’s pedal analyses — circuit-level walkthroughs of classic fuzz, overdrive and booster circuits (Big Muff, Tube Screamer, Fuzz Face…): the white-box companion to this app’s black-box measurements. The site (electrosmash.com) is offline, so the citation is the Internet Archive’s capture of 18 January 2024 — a permalink, and still attributable to the original author. A community mirror at electrosmash.mas-effects.com was live when this was written; it is a convenience, not the citation.
The Reading Room. The website carries a companion track to this guide at pedalscope.com/reading/: short articles on why a measurement matters to a musician — the hearing and the physics between a figure on a record and what reaches your ears, one question per page, every number recomputed from a formula given in the text. The guide says what a chart means; the Reading Room says why it matters to the way a chord sounds in a room. It lives on the website only and opens in your browser.
Trademarks
Product, brand, and company names appearing in PedalScope or its documentation are trademarks or registered trademarks of their respective owners. None of those owners is associated or affiliated with PedalScope or its developer, and no endorsement is implied. These names appear solely to identify products that were independently measured, or whose manufacturers’ published documentation is cited. PedalScope is developed independently in Québec, Canada.