Inspect the full 0–500 Hz response beside the selected peak’s frequency-isolated tap ring-down.
0–500 Hz response with the selected peak and -3 dB bandwidth.
Blue: isolated tap. Gold: envelope. Dashed gold: fitted decay.
These measurements travel with the detected plate modes into the Plate Thickness calculator.
Resonance Reader is a browser-based FFT audio analyzer for modal testing and tuning of instrument materials and acoustic instruments. It was built to make the measurement and modal-tuning techniques in Trevor Gore's books easier to put into practice. It helps luthiers build and fine-tune their instruments, and helps players understand the response they hear and feel.
Record a tap or import an audio file to locate resonances in a top or back plate, a piece of brace stock, or an assembled instrument. Inspect their frequencies and decay, then compare measurements before and after a change.
When you tap a guitar or plate, you excite several resonances at once. When you play a note on a string, the string and the instrument's resonances interact, shaping how the note starts, develops and fades. Resonance Reader lets you examine both.
Start with the Default FFT profile. For instrument body tests, damp the strings so their ringing does not obscure the body response. Use a clean tap that does not overload the recording; reduce the input level or tap more lightly if the waveform is visibly flattened at its largest excursions.
A mode is a particular pattern of vibration. A plate can bend mainly along the grain, bend across it, or twist. Each pattern has a natural frequency and a rate at which its vibration dies away. When the structure responds strongly near one of those natural frequencies, you are seeing a modal resonance.
In an assembled guitar, the top, back and enclosed air interact. Air, Top and Back describe the main character of a response; they do not mean the other parts have stopped moving. Modal tuning uses those resonances to guide and check structural changes. It is different from tuning the strings, and it does not mean every instrument should have the same frequencies.
FFT means Fast Fourier Transform. It separates a section of recorded audio into frequency components. The waveform tells you what happened over time; the spectrum tells you which frequencies are present in that section.
With a played note, many peaks belong to the string's fundamental and partials, often near two, three or more times its fundamental frequency. They are not automatically separate body modes.
Although the graph is called Frequency Response, a microphone-only tap spectrum is not a force-normalized frequency response function. Without measuring the input force, it cannot tell you the structure's absolute mobility. Peak height also depends on the tap and recording setup.
Recording or importing another take keeps the preceding take available for comparison, within the take limit. Keep capture conditions and display scaling comparable. A taller trace does not by itself mean better wood or a more responsive instrument.
Moving a selection changes the analysis, not the saved audio. When tap averaging is enabled, the spectrum can combine accepted taps instead of displaying one raw FFT of the highlighted region.
Hover over the spectrum to read frequency and level. The plot toolbar provides zoom, pan, reset axes and image download controls. Zoom changes what you see, not the navigator's analysis region.
Mode cards and markers identify assigned physical modes. See Correcting a peak or mode assignment for the drag and reset steps. A target is a frequency you want to explore, not one measured in the recording.
The 4DOF Model toggle adds a modeled response in Instrument mode. It does not turn that curve into measured data. Stock workflows provide their corresponding calculator actions instead.
An automatic label can land on the wrong peak. Correcting its assignment tells the tool which part of the measured spectrum to use; it does not move the actual resonance or alter your recording.
Dragging the text box only moves the label for readability; it does not change the assigned frequency. You do not need to enable 4DOF to drag a measured-mode pointer. Clicking the card, including its pencil symbol, selects it for inspection rather than opening a measured-frequency entry field. Choose Peak / Q in Measuring to show that inspection view.
In Instrument, choose the small reset link on the corrected mode card. If it is hidden, turn on 4DOF Model to expose it; you can turn the model off again afterward. This removes that mode's manual assignment and returns it to the current automatic result. It keeps the recording and does not clear a separate target.
The card reset is currently not exposed in Plate Stock or Brace Stock. You can correct those assignments by dragging their pointers. Reset in the Settings dialog restores FFT settings; it is not the mode-assignment reset.
In Instrument with 4DOF Model enabled, Set target enters a frequency for a modeled what-if comparison. Type the target and press Enter or leave the field to apply it. Press Escape to cancel an edit. To remove a target, empty its field and press Enter. None of these actions reassigns the measured peak.
Select the intended tap, then click a peak dot or use the previous and next peak arrows. This changes the peak being inspected; it does not relabel Air, Top or Back. For plate or brace stock, it also leaves a confirmed Long assignment unchanged. To replace that confirmation, select the correct peak and choose Use … Hz as Long beside the stock summary. Clear Long removes the confirmation.
If the peak you expect is not visible, check the frequency range, selected tap, support and tap position. A manual assignment cannot recover a resonance that the recording did not capture clearly.
Open Settings from the spectrum toolbar. Start with Default and change one setting at a time when investigating a measurement.
Turn Tone on, then move the pointer across the main spectrum to hear a sine tone at that frequency. On a touch screen, move your finger across the spectrum; lifting it holds the last frequency. While Tone is on, a touch sweep controls frequency rather than panning. Turn Tone off when finished.
For Chladni-pattern work, pair a suitable Bluetooth speaker with your device and select it as the audio output. It needs enough output at the frequency being tested to excite the plate. An amplifier and exciter can also be used. The app supplies the tone; the physical pattern forms on the plate, not on the screen.
In a Chladni test, a light sprinkling of dried herbs, glitter or fine sand moves away from strongly vibrating areas and collects near the nodal lines, where the plate moves least. This makes the vibration pattern visible. Choose a material that will not scratch or stain the surface, especially when testing a finished instrument.
Support and excitation matter: attaching a driver or adding mass can change the response. Start with low output volume. Hearing the tone is not itself confirmation of a mode; observe the physical response. Keep tone playback out of tap recordings unless it is deliberately part of the test. See UNSW's explanation of guitar-plate Chladni patterns.
Use Instrument to locate the main body resonances and compare how they change. Record separated taps with the strings damped, keeping support and microphone position consistent.
The optional 4DOF Model fits a simplified coupled model to the assigned frequencies. Targets explore a proposed change; they are not measurements or instructions to remove material. Ask whether an intervention moved the intended resonance, and what else moved with it.
Use Played Note to examine how a note develops and decays, especially when something you hear is not clear in a tap spectrum. Record a clean note with room for its decay. Keep plucking position and attack similar; damp the other strings for a controlled comparison.
The time axis and hover readings show elapsed time from the start of the green selection. Look for beating, a partial that fades abruptly, or decay that differs from neighboring notes. Repeat the recording to check whether the behavior persists.
Despite its name, Energy Transfer does not directly measure energy flowing from the string into a body mode. It tracks signal near selected frequencies. A nearby string partial and body resonance can overlap; use the view to investigate, not to declare a cause from one trace.
Use Plate Stock to identify bending modes in a top or back plate before a material or thickness calculation. Support and excite the sample so the mode of interest can move; holding it where that mode moves strongly can suppress its response.
Measure the actual sample. A wrong thickness or mode assignment can produce a plausible but wrong material estimate. A shaped, braced or assembled top can have useful resonances to inspect, but is not equivalent to the rectangular sample used by the stock calculation.
Use Brace Stock to characterize the wood you will cut braces from, not to set finished-brace dimensions. Start with a reasonably uniform rectangular sample and let it bend freely enough to reveal the longitudinal bending mode.
You can edit measurements, clear the confirmed Long assignment, or confirm a different peak. Do not keep an assignment just because it produced a reasonable modulus. This estimate needs one longitudinal bending mode, not the three plate frequencies. It does not establish the strength or long-term safety of a finished brace.
Use Peak / Q to examine one resonance and how confidently its width and decay can be measured. Enter from any analysis view. For stock characterization, Add measurements identifies the specimen here; there is no need to switch through Plate Stock or Brace Stock first.
Bandwidth is the resonance width at 3 dB below its peak. Spectral Q is peak frequency divided by that bandwidth. A narrower peak has higher Q, provided the peak and both bandwidth crossings are resolved.
On the right, the blue trace is the selected tap filtered around the selected resonance, not the full-frequency WAV. Solid gold is its amplitude envelope. Dashed gold is an exponential decay fitted to a usable portion of that response. Vertical markers identify the fitting interval when a fit is available.
The amplitude scale is relative, not physical displacement or calibrated sound pressure. A fit extending beyond the observed response is a projection, not more recorded data. Depending on settings, the spectrum may average accepted taps; the ring-down belongs to the selected tap.
At the same frequency, higher Q generally means slower decay. It is not a wood-quality score or a direct prediction of every played note's sustain. For a builder, the useful comparison is whether a particular resonance became more or less damped after a change, and whether that repeats.
The decay analysis looks for a usable decline after the envelope maximum, estimates background noise from suitable quiet regions, and avoids fitting the tail too close to that noise. It checks nearby peaks and sensitivity to isolation bandwidth. Without a suitable quiet reference the fit is provisional; a short, contaminated or unstable response may not support a trustworthy estimate.
Leave more space between taps, reduce background noise and check another tap rather than forcing an answer. Export peak data retains the selected peak and available evidence, including decay-derived Q and fit diagnostics. Disagreement between spectral Q and decay Q is something to investigate, not a reason to choose the more attractive number.
Add measurements opens the same editor used in Plate Stock and Brace Stock, even when you came here from Instrument. Identify the specimen as Plate or Brace stock and enter its dimensions and mass. Change lets you correct an existing specimen type; Apply clears an incompatible Long confirmation. Cancel leaves the saved measurements and confirmation unchanged. Neither action changes the analysis view.
Confirm the specimen's first Long bending mode with Use … Hz as Long. The summary shows calculated longitudinal sound speed and dynamic long-grain Young's modulus. Expand it for density and, for brace stock, specimen EI. Q is not an input to those estimates; a selected peak and its Q alone are not enough.
The plate estimate uses the Plate Thickness calculator's free-free rectangular plate model, with length along the grain. Long alone supports its longitudinal estimate; Cross and Twisting are still needed for the full thickness calculation. Finished guitar dimensions or an arbitrary body peak do not characterize the wood. Use a suitable stock specimen and physically check the mode.
Use the calculator action for the current workflow, then review the transferred inputs. A handoff supplies inputs, not an ongoing link that keeps two tools synchronized. It does not include the audio recording.
Confirm Air, Top and Back, then enable 4DOF Model to fit the simplified coupled model. Open in 4-DOF model carries the available fitted parameters into the dedicated tool. A solved what-if target model takes priority over the baseline fit, so check which scenario you intend to transfer. Without a fit, the link opens the tool without fitted parameters.
A fit lets you explore modeled changes. It does not independently measure the instrument's masses and stiffnesses.
Open in Plate Thickness calculator sends confirmed Long when available, other compatible plate frequencies, and the sample measurements you applied. Body resonances are not relabeled as Cross or Twisting. Without measurements, it sends available frequencies alone. Defaults at the destination are not measurements of your plate.
The calculator estimates density, long- and cross-grain moduli, their ratio and the shear modulus used by its plate model. You supply the intended body dimensions and target frequency to calculate thickness and projected mass. The transfer does not choose the right target for your instrument.
Open in Brace Calculator uses the measurements already entered here. With a confirmed Long mode and valid measurements, it carries the calculated density and long-grain modulus. Otherwise it sends available frequencies alone. Enter the geometry of the brace you intend to cut at the destination; the tested stock dimensions are not silently used as finished-brace dimensions.
In Brace Stock or Peak / Q, enter sample measurements and confirm Use … Hz as Long. Match in Flexural Rigidity carries that confirmed frequency, specimen dimensions and mass, source label, and calculated density, modulus and sound speed.
Match compares the plan with that material and explores width and height adjustments. Review the proposal before applying it. The destination calculates EI from material modulus and designed geometry; the stock's own EI is not the EI of every brace cut from it. Inspecting a different peak does not silently replace your confirmed Long assignment.
Save applies to the current take, not the entire list of comparison takes.
Check the available Save action before closing the page. Save your source audio as well as any analysis results you need.
Export peak data is a separate analysis export, not a replacement for saving the source audio. Remembered browser state is convenient for moving between tools, but should not be your only copy of a measurement. Save the recordings you need before clearing takes.
The FFT describes the selected signal's frequency content. Tap averaging combines accepted spectra in the power domain. The default tap-spectrum analysis uses a 400 ms window with 100 ms of pre-onset context. Those are analysis settings, not a claim that the response lasts 400 ms.
A finer FFT grid can help locate a peak between widely spaced bins. Padding does not create more recorded decay or separate modes the available signal cannot resolve.
Spectral and decay Q use different features of the response, but both depend on analysis choices. Frequency isolation changes the signal used for the fit, so agreement is a useful cross-check, not fully independent proof. An exponential approaches zero; it never reaches an exact stopping point.
Dimensions, mass, mode identity, geometry and support conditions must suit the material model. A clean frequency reading cannot compensate for a wrong thickness or a wrong mode.