A free online audio spectrum analyzer: watch live frequencies from your microphone or a file, with peak hold and 1/3-octave bars. No install.
The audio spectrum analyzer shows which frequencies are present in a sound right now, from 20 Hz on the left to 20 kHz on the right, with level in decibels up the side. Point it at your microphone or open a file and play it through the page. The line view draws the full spectrum; the 1/3-octave view groups it into 31 bars, the layout used on graphic equalisers and room-tuning gear. Peak hold keeps a marker at the highest level each frequency has reached, Freeze stops the display so you can study it, and the readout names the strongest frequency and its nearest musical note.
Use it to find the pitch of a hum or a ringing resonance before cutting it with the equalizer, to see where a mix is heavy or thin, or to check what a room adds while you play pink noise through your speakers. Readings from a microphone include the microphone's own response, so treat a phone or laptop mic as a guide to where the peaks are rather than a calibrated measurement. The microphone signal is analysed on your device, is not recorded, and is released when you press Stop. To see how the frequencies in a whole file change over time, use the spectrogram.
It shows how the energy in a sound is spread across frequency at this moment. Bass appears on the left, treble on the right, and the height of the line or bar is the level in decibels. A pure tone is a single spike, while speech and music form a changing shape across the whole range.
A spectrum analyzer shows one moment at a time and updates continuously, so it suits live sound. A spectrogram keeps every moment and lays them side by side as an image, so you can see how the frequencies in a whole recording change over time. Use the analyzer to watch and the spectrogram to inspect.
The frequency of a peak is accurate, so it is reliable for finding the pitch of a hum, whistle, or resonance. The levels are not calibrated: built-in microphones roll off the lowest bass and have an uneven response, and browsers do not report absolute sound pressure. Treat the shape as a guide, and use a measurement microphone with dedicated software for calibrated work.
Line plots the spectrum in fine detail across the whole range, which is best for spotting narrow peaks such as a single note or a resonance. The 1/3-octave view groups roughly 20 Hz to 20 kHz into 31 bands, each a third of an octave wide, the same spacing as a 31-band graphic equalizer, and each bar shows the strongest reading within its band. Bars make the overall tonal balance easier to judge at a glance. Switching views resets the peak hold.
Read Strongest frequency below the graph. It names the loudest frequency above 20 Hz, with the nearest musical note and its level, refines the estimate between analysis bins, and updates about five times a second. A larger FFT size, such as 16384, gives finer frequency detail but reacts more slowly, and Freeze holds the display while you read it. If something louder is sounding at the same time, the readout follows that instead.