FAQ

Why doesn't PedalScope use AI?

Because it's a measurement instrument, and an instrument's only asset is that you can trust its numbers. Every value PedalScope shows you is computed deterministically from audio that passed through your device: the same measurement gives the same answer, and every chart can be traced back to the capture it came from. The plain-language summaries in the app are generated from your measurements by fixed, hand-written rules — no generative model, nothing leaves your Mac, and the summary can never say anything the numbers don't support. A description that might be eloquently wrong is worthless on a test bench. So the honest answer is: not "AI wasn't available," but "an instrument shouldn't guess."

Why is PedalScope Mac-only?

Because the measurement quality comes from how deeply the app sits on one platform. PedalScope binds directly and explicitly to the audio interface you choose — it refuses to run through a hidden sample-rate conversion, never touches your system's default devices, and its real-time capture code is isolated by the Swift compiler itself, not just by careful programming. That level of control is only possible by committing to one audio stack and doing it properly. PedalScope is also built by one person; one platform done rigorously beats three platforms done approximately — and for a tool whose entire job is accuracy, that trade isn't close.

Why isn't PedalScope open source?

The app itself is a commercial product because that's what keeps it independent: development is funded by people who buy it, not by sponsorships or review units from the companies whose products it measures. (PedalScope accepts no money, hardware, or licenses from makers of anything it might judge.) But the parts of the project where openness actually builds trust are open or heading there: the measurement methods are documented in full in the user guide, your data is yours in a documented export format, and the hardware reference box used to validate the instrument is planned for open release — schematics and layout — so anyone can build one and check the instrument's answers themselves.

How do you validate the measurements?

Against answers known before anything is plugged in. I built a hardware reference box whose distortion behavior is determined by resistor arithmetic and Fourier theory — for example, one circuit in it must produce a harmonic ratio of exactly −13.98 dB. PedalScope measures −14.0. Every analysis algorithm is additionally tested in software against closed-form mathematical ground truth on every build, key results are cross-checked against an independent implementation in a different language, and the plugin-measurement path is verified against a unit that should measure as perfectly clean — PedalScope reads its distortion at the numerical floor, around −174 dB. When the app tells you two pedals differ by 3 dB somewhere, that number has been through all of that. The full validation story is in the user guide.

I'm a guitarist / pedal designer / recording engineer — what do I actually do with this?

Guitarists: see why your pedals sound the way they do — and shop or argue with evidence. Compare two drives on the same charts, see which one cleans up under a light touch and which one never does, and find out whether that boutique pedal actually behaves differently from the classic it's compared to.

Pedal designers: a bench instrument for iteration. Measure a prototype, change one component, measure again — PedalScope resolves changes as small as a single swapped diode — and keep every revision's fingerprint as a permanent, comparable record of the build.

Recording engineers: decide plugin-versus-pedal questions with data instead of forum threads. Measure the hardware unit and the plugin at matched levels and see precisely where they agree and where they part company — and know how hard you can push a drive before its character changes.

What about impedance? Don't I need a re-amp box between my interface and the pedal?

It depends on the pedal, and PedalScope is honest either way. An audio interface's line output is a low-impedance source, while a guitar pickup is not — and some circuits care about that difference. Most classic overdrives and distortions with buffered or op-amp inputs (the Tube Screamer family, most modern pedals) behave essentially identically from either source. Vintage-style fuzzes are the big exception: their input stage interacts strongly with what's driving them, and a fuzz measured from a low-impedance source is genuinely a different measurement than one driven from a pickup-like source. For those, a re-amp box or a simple series-resistor fixture restores pickup-like conditions — and PedalScope lets you record the fixture as part of the measurement's identity, so a fingerprint always says exactly how it was driven. Either way you get a true measurement of the pedal as it was actually driven; the fixture just needs to be part of the record, and the app makes sure it is.

Can PedalScope profile an amp?

No — and please don't try by connecting an amplifier's speaker output to your audio interface, which can damage the interface. PedalScope measures pedal-level devices: anything that takes an instrument- or line-level signal in and puts one out (which includes amp sims and drive plugins, hosted directly). It does not measure amplifiers. A real amplifier's speaker-level output, its reactive load, and its power-stage behavior are outside what this instrument measures, and the app says so wherever an amp could be connected. If you're even thinking about it, read Safety: amplifiers first — a tube amp must always drive a proper load, and speaker-level signals destroy line inputs.

Can I compare my measurements with someone else's?

Yes — if you both measure at the same stated condition, and PedalScope is built to make that condition checkable rather than remembered. A drive pedal's behavior depends on how hard it's driven, so two measurements only overlay if the drive level, the source, and the loading match. Every PedalScope measurement records its source fixture and embeds its calibration, and once you've entered your rig's volts-per-dBFS factor (one scope or multimeter reading of the app's built-in calibration tone), drive levels are stated in volts — which are portable between rigs in a way interface-relative numbers never are.

The standard condition is called PSC-1: 168 mV peak at the pedal input with the standard sweep, driven direct (or through a declared 10 kΩ fixture for vintage-style fuzz), into a high-impedance input, on a clean same-session calibration. Two PSC-1 measurements of the same unit are comparable. The guide has the complete definition. The app grades this for you: a Harmonic Distortion record whose recorded provenance meets the condition wears a PSC-1 badge quoting the condition string, and that string rides the provenance strip of every chart you copy or save from it. A record without the badge shows nothing — most measurements are exploration at whatever drive the question needed — and hovering its calibration chip explains what would need to change, or that its calibration carries no volts factor to check against. The badge asserts recorded provenance, nothing more.

One honest caveat: two units of the same pedal model measured perfectly can still differ — see the next question.

See also: How do you validate the measurements?

My clone measures differently from the original. Is it wrong?

Not necessarily — and PedalScope will never tell you it is. Two originals off the same production bench differ: carbon-comp resistors drift, diode forward voltages scatter, germanium transistors vary widely. PedalScope resolves changes as small as a single swapped diode, which means it also resolves the natural spread between two "identical" originals. A difference smaller than that spread is not a verdict about your build.

That's why the app reports differences as measured quantities ("H2 differs by 3 dB at this note") and never as judgments. When comparing a clone to an original, treat single-unit references as one sample, not ground truth — the original you measured is one point in its model's population. Putting real numbers on typical unit spreads for classic circuits is planned work (it requires measuring many units of the same model, which is exactly the kind of study this instrument exists for). Until then, the honest position is that nobody — including me — knows the typical spread for any given circuit yet. Which is itself the reason not to read a small measured difference as a defect.

Why not just use REW? It's free.

I'm a longtime REW user, and if you want a free, cross-platform audio analyzer, I genuinely recommend it — its distortion measurement uses the same log-sweep family of methods PedalScope builds on. The difference is what the two tools are for. REW is built for rooms and loudspeakers: its questions are flatness, decay, and THD, and its workflow assumes you know why you're asking. PedalScope is built for distortion effects: it measures the musically meaningful quantities — touch response across drive level, even/odd harmonic balance, what a two-note chord invents, how character shifts as you dig in — keeps every measurement in a library with its calibration and control settings attached, explains results in plain language generated from the numbers, and lets you listen to what it found, loudness-matched. And the whole instrument is validated against a hardware reference box with answers known from circuit theory before anything is plugged in. If you want a general-purpose audio analyzer, use REW. If your question is "what does this pedal actually do, and how is it different from that one," that's what PedalScope is for.

What audio interface do I need? Does anything need calibrating?

One audio interface that both plays and records, wired into a loop: the app plays a test signal out of the interface's first output pair, through the pedal, and reads it back on one input of the same device. Any reasonably clean duplex interface does that. PedalScope calibrates the loop itself, every session: it measures your interface's flatness, noise floor, and round-trip latency directly, embeds that calibration in every measurement, and warns you if the rig's floor limits what a measurement can claim. There is no external calibration gear and no trusting a spec sheet — the app measures your actual rig. A Scarlett-class interface is entirely adequate — the reference rig is one.

What matters when choosing: an honest noise floor, reasonably flat response (the app measures and compensates level, and tells you the flatness it found), and separate input/output jacks you can wire into a pedal loop. One optional extra: entering your rig's volts-per-dBFS factor (a single multimeter or scope reading of the app's calibration tone — a steady sine at a known level, made for exactly this) upgrades level readouts from interface-relative to absolute volts, which is what makes measurements portable between rigs.

A Mac on its own is not a measurement rig. Its built-in speakers and built-in microphone are two separate devices, and the loop has to play and record through one device, so that calibration and measurement traverse the same electrical path on one clock. Combining the two in a macOS aggregate device is not a supported path: an aggregate that spans two clock domains applies drift correction, and drift correction is resampling, which the measurement path forbids in as many words. (Whether the built-in devices in fact share a clock is measurable and has not been measured; the route is unsupported, not proven impossible.) The headphone jack's TRRS microphone contact is a microphone input — it supplies a bias voltage and expects millivolts — so a pedal's output overloads it, and the bias puts DC on the pedal's output jack. Use an interface with a line output and a line or instrument input, and run the loop through it.

Are there pedals this method can't measure?

Yes, and PedalScope is built to tell you when it meets one. The measurement assumes the pedal's behavior holds still during a sweep — true for the classic overdrive/distortion/fuzz families. It is NOT true for effects whose behavior changes over time: heavy sag, envelope-dependent gating, blocking distortion that recovers slowly, compressor-like behavior, or anything with modulation in the path. Those devices produce plausible-looking charts that are actually artifacts of a moving target.

The instrument's defenses are measurements, not disclaimers: every transfer curve carries a memory metric that flags behavior a static curve can't explain, and render determinism checks catch chains that don't repeat (in one documented case, a plugin's default preset failed repeatability by 22 dB — the app's gates flagged it three separate ways before any conclusion was drawn). When the instrument says a device is outside the method, that IS the finding: "this pedal's character is time-dependent" is a true and useful thing to know about it — it's just not a fingerprint.