IMD Test Online — Distortion Check
Test intermodulation distortion with SMPTE and DIN twin-tone pairs and sideband readouts. Learn how IMD spectra read. Free in your browser, no download.
Protect your hearing. Start at a low volume. Never raise the volume to make a tone audible. Levels are shown in dBFS, relative to full scale — not SPL.
How it works
Two-tone signals are synthesized live in your browser with the Web Audio API. Nothing is uploaded or recorded. Levels are reported in dBFS, relative to full scale.
Intermodulation distortion is what makes overloaded gear sound harsh rather than warm: new frequencies that were never in the music. This page plays the two standard two-tone signals and shows exactly where their distortion products must fall.
SMPTE 60 Hz + 7 kHz and DIN/CCIF two-tone
SMPTE stresses low-frequency modulation of a high probe. CCIF stresses the top octave where tweeters and converters work hardest. Both tones play together from a user gesture with a persistent Stop, and every level is dBFS, relative to full scale.
Expected products
The readout lists 2f2−f1 and 2f1−f2 for the active pair. Open the spectrum analyzer in another tab while this plays to see whether sidebands rise around the probes — but keep the volume conservative, especially for the 19–20 kHz pair.
Frequently asked questions
What is intermodulation distortion?
When two tones pass through a nonlinearity, extra tones appear at sums and differences such as 2f2−f1 and 2f1−f2. Unlike harmonics, these products are usually not musically related to the signal.
What is the SMPTE test?
SMPTE plays 60 Hz and 7 kHz together at a 4:1 amplitude ratio. Distortion shows as sidebands modulating the 7 kHz probe tone.
What is the CCIF/DIN test?
CCIF plays two closely spaced high tones such as 19 kHz and 20 kHz. The 1 kHz difference product and nearby tones expose high-frequency nonlinearity.
Can this measure my device?
No. Without a calibrated loopback the page demonstrates the signals and computes expected product frequencies. Treat audible harshness as a hint, not a number.