RTA Analyzer — Audio Spectrum

How to use this free online audio tool

What can a free online RTA show?

This browser-based spectrum analyzer shows the relative frequency content reaching your selected microphone or audio interface. It can help identify a persistent low-frequency hum, compare the overall tonal shape of two sources, or locate a narrow ringing frequency while troubleshooting a PA system. Unlike a calibrated measurement rig, the reading depends on your microphone, input processing, gain and environment. Microphone access is requested only when you choose to start the analyzer, and audio analysis is performed locally in the browser.

The RTA Analyzer is a real-time audio-frequency viewer designed for quick AV system checks. It uses your browser's microphone input to show where incoming signal energy sits from bass through treble. It can help a technician locate obvious hum, feedback-prone bands, resonances, or differences between signal sources. It is not a calibrated measurement microphone, sound-level meter, or replacement for room-tuning software.

Start with a clean input path

Connect the intended microphone or USB audio interface before opening the analyzer. Press Start microphone and approve browser access. The tool requests disabled echo cancellation, noise suppression, and automatic gain control, although the actual processing can vary by device and browser. Point a measurement microphone consistently, avoid handling noise, and keep input gain from clipping. The status display reports whether the browser could start the input stream.

1/3-octave versus FFT

The 1/3-octave display combines neighboring FFT bins into familiar frequency bands. It is useful for seeing broad tonal trends without hundreds of narrow peaks. The FFT view shows more detail and can reveal a narrow whistle or hum that broad averaging might hide. Increasing the FFT size creates narrower frequency bins, but slows how quickly a newly arriving event influences the displayed spectrum. Smoothing helps with fast-changing content but can hide brief peaks.

How to read frequency regions

Very low bands around 31.5–63 Hz often show stage rumble, HVAC vibration, or sub-bass energy. Around 125–500 Hz, look for low-mid buildup and room resonances. Between about 1–4 kHz, speech intelligibility and many feedback-related sounds become prominent. At 8 kHz and above, high-frequency hiss and sibilant content are easier to see. These are broad diagnostic categories, not equalizer instructions: investigate the source before cutting or boosting a band.

Understanding dBFS and the input peak

The graph uses relative levels derived from Web Audio FFT data. It does not represent sound pressure in dB SPL. The input peak readout represents the largest absolute amplitude seen in the current time-domain buffer. Values near 0 dBFS can indicate that the sampled digital waveform is approaching full scale. Audio hardware may already have clipped before the samples reached the browser, so inspect physical gain stages if distortion is suspected.

Use peak hold and exports

Turn on peak hold to keep track of recent dominant bands, and clear the overlay before a new test. Freeze the display to examine a moment in time. Export a CSV snapshot containing the visible spectrum frequencies and estimated relative levels, or save the canvas as a PNG for a production note. These files are saved on your computer; the analyzer does not upload microphone audio.

Common questions