Response curve → perception
Upload a screenshot or import a response file, correct the curve, then calculate stationary Zwicker loudness: total sones, loudness level in phons, and specific loudness in sone per Bark.
First time here?
Start with a clear chart image or import an exported response file. Every path ends with editable frequency and level data.
Choose a chart image with visible frequency and dB labels, or directly import CSV, TXT, FRD, or a Room EQ Wizard measurement-text export. Files stay on your device.
For an image, use Suggest axes and check the green rectangle. Imported files go straight into the editable curve table; review the points and select the correct SPL basis.
For an image, use Extract coloured curve and correct the orange trace. For any imported file, choose the y-axis meaning before relying on a loudness result.
01 / Digitize
REW: choose File → Export → Measurement as text, then import its .txt or .frd file. Binary .mdat projects need this export step.
●Upload an image to suggest axes and find a coloured trace.
One frequency, dB pair per line. Exact values here and drag edits both feed the calculation.
03 / Perception
Total loudness
—soneWaiting for a calibrated curveLoudness level
—phonDerived from total loudnessInput status
ISO pathFree-field correctionShape the next version
Saved projects, batch conversion, and exportable reports are candidates. Tell us which would be most useful.
25 Hz — 12.5 kHz
0.1 to 24 Bark
A / B perception
Save a calibrated “before” curve, then upload or edit a second curve. The difference view shows what changed in total loudness and across the Bark scale.
Finish a calibrated calculation first. Relative or unanchored traces cannot be used as a loudness baseline.
Loudness guide
These terms describe related parts of hearing perception. This calculator uses them to show why a plotted sound-pressure response is not, on its own, a loudness result.
Sones express perceived loudness. Phons express loudness level on the equal-loudness scale referenced to a 1 kHz tone. The app reports both from the calculated total loudness.
The Bark scale represents auditory critical-band position. Specific loudness, N′(z), shows how much loudness falls in each Bark band; total loudness is the area under that pattern.
Fletcher–Munson is a historical name for equal-loudness contours. They illustrate that equal physical SPL at different frequencies does not sound equally loud. Zwicker loudness is a fuller critical-band calculation, not an A-weighting curve or a Fletcher–Munson contour generator.
Yes, when its y-axis is calibrated SPL or when a transfer-function trace can be anchored to a declared 1 kHz SPL. An uncalibrated relative response can be digitized, but it does not contain enough level information for a loudness calculation.
No. It calculates stationary Zwicker loudness from the declared spectrum. The equal-loudness contours are useful background for understanding frequency-dependent hearing, but they are not the calculation output here.
The stationary Zwicker method applies different hearing corrections for free-field and diffuse-field listening. Choose the setting that matches how the source and listener were measured or intended to be heard.
Method notes
The calculation uses the stationary 28-band Zwicker method: low-frequency grouping, ear-transmission correction, free/diffuse-field correction, core loudness, level-dependent upward masking, and integration of a 0.1-Bark specific-loudness pattern.
The exact kernel is appropriate for the declared 1/3-octave SPL input. Image digitization, a narrowband curve sampled at band centres, or anchoring a transfer function with one reference level add uncertainty before that kernel. This app labels those cases; it does not turn them into certified measurements.
It does not model time-varying loudness, binaural effects, microphone/calibration uncertainty, room interaction, or signal bandwidth absent from the image.
Method implementation adapted from the MIT-licensed ZwickerLoudness.jl stationary reference implementation. ISO 532-1 is a standard; this app is not a certification tool.