What is a spectrum analyzer?
A spectrum analyzer takes a sound and splits it into the individual frequencies it is built from. Instead of the single wiggling line you see in a recorder app, you get a chart: frequency along the bottom, loudness up the side. A hum shows up as one tall spike. A cymbal shows up as a wide smear across the top of the range.
The tool above is a free online spectrum analyzer. It runs entirely in your browser using the Web Audio API, so there is nothing to install and nothing to sign up for. Point it at your microphone to analyse a room, an instrument or a noise you are trying to identify, or load an audio file to look inside a recording you already have.
The same instrument goes by several names, and they all mean this. An audio spectrum analyzer or sound spectrum analyzer is one tuned to the range humans can hear, roughly 20 Hz to 20 kHz — that is what this page gives you. A frequency analyzer or sound analyzer is the same idea described by what it measures rather than what it draws. A spectrogram analyzer plots that spectrum against time instead of showing a single instant, which is the second view in the selector above. And if you learned the word in the UK, Ireland, Australia or New Zealand, you will have spelled it spectrum analyser — same instrument, same page.
One distinction is worth making. In electronics, a spectrum analyzer usually means a bench instrument for radio frequency work, measuring signals in the megahertz and gigahertz range. No browser can do that, because your computer has no antenna and its sound card stops well below 100 kHz. An online spectrum analyzer is an audio instrument. If you need RF, you need hardware.
How to use this online spectrum analyzer
- Choose a source. Press Microphone and allow the permission prompt to analyse live sound in the room. Press Audio file — or drag a file straight onto the display — to analyse a recording. WAV, MP3, OGG, FLAC and M4A all work.
- Read the peak. The large number is the strongest frequency present right now, in hertz, with the nearest musical note underneath. The list beside it holds the five strongest frequencies, which is what you want when a sound has more than one component — a chord, an engine, a room with two resonances.
- Switch views and export. Spectrum shows this instant. Spectrogram scrolls the last few seconds so you can watch a sound change over time. Export PNG saves the current display with the peak reading printed on it, ready to attach to an email or a forum post.
The FFT size control is the one setting on this spectrum analyzer worth touching. It trades detail for speed. A larger size separates two close frequencies more cleanly, which helps with low bass notes, but it responds more slowly to sudden changes. 4096 is a sensible default; move up to 16384 when you are trying to pin down a steady low-frequency hum, and down to 2048 when you want the display to react instantly to speech or percussion.
How to read a spectrogram
Switch the view to Spectrogram and the chart changes meaning. Time now runs left to right, with the newest moment at the right edge. Frequency runs up the side, low at the bottom. Loudness is no longer height — it is colour. Dark blue is near silence, teal is moderate, and green through amber marks the loudest content.
That turns sounds into shapes you can recognise at a glance. A steady tone draws a flat horizontal line. A note with harmonics draws a stack of parallel lines evenly spaced above the fundamental. Speech draws stacked bands that bend and slide as the vowels change. A door slam draws a vertical stripe crossing every frequency at once. Background hum from a transformer or a fridge draws a stubborn horizontal line low down that never goes away — which is exactly how you find it.
The frequency scale on both views is logarithmic, not linear. Each doubling of frequency takes the same amount of space, so an octave is the same width at the bottom as at the top. That matches how hearing works and stops the bass, where most musical information lives, from being crushed into a sliver at one end.
Common frequency ranges
When the spectrum analyzer shows you a number, this is what tends to live there.
| Range | What lives there |
|---|---|
| 20 – 60 Hz | Sub-bass. Felt more than heard: kick drums, distant traffic, building rumble. |
| 50 / 60 Hz | Mains hum. 50 Hz across most of the world, 60 Hz in North America. A spike sitting exactly here is almost always electrical. |
| 60 – 250 Hz | Bass. The fundamental of most male voices, bass guitar, the low end of a piano. |
| 250 – 2000 Hz | Midrange. Where nearly all speech intelligibility lives, and most instruments' fundamentals. |
| 2 – 5 kHz | Presence. Consonants, the attack of a snare, the part of the spectrum ears are most sensitive to. |
| 5 – 12 kHz | Brilliance. Cymbals, sibilance, the sense of air in a recording. |
| 12 – 20 kHz | The top. Many adults stop hearing above 15 kHz; the range narrows with age. |
| 440 Hz | Concert A above middle C — the reference the note readout is calculated from. |
What people use it for
Checking a mix
Load a track and see whether the low end is piling up or the top is dull, without trusting headphones you already know are lying to you.
Tuning a room
Play a sweep through your speakers, run the spectrum analyzer on your microphone, and watch which frequencies the room boosts and which it swallows.
Tracking down a noise
Find the exact frequency of a hum, whine or buzz. The number narrows the suspect list fast, and the exported PNG gives you something concrete to show a landlord or a technician.
Checking your hearing range
Play tones from a signal generator and confirm what the analyzer sees against what you can actually hear. Useful for curiosity — not a substitute for an audiologist.
Teaching and learning
Show a class what a Fourier transform actually does by singing into it. Harmonics, timbre and octaves stop being abstract once they are on screen.
Identifying a note
Point it at an instrument, a bird, or a bell and read the pitch. The note name and cent offset appear under the peak frequency.
Frequently asked questions
Is this online spectrum analyzer free?
Yes, completely, with no account, no trial and no limit on how long you use it.
Do I need to install anything?
No. It is a web page. It works in Chrome, Edge, Firefox and Safari on desktop and on phones. On iOS, microphone access requires Safari or a browser using the Safari engine.
Is my audio uploaded anywhere?
No. Both the microphone stream and any file you open are processed locally by your browser's audio engine. Nothing is sent to a server, because there is no server involved in the analysis.
What is the highest frequency it can show?
Half your device's sample rate — usually 24 kHz for a 48 kHz sound card. The display is capped at 20 kHz, which is the top of human hearing.
How accurate is the peak frequency reading?
The reading is refined between FFT bins by interpolation, so a clean steady tone typically reads within a hertz or two of its true value. Noisy or rapidly changing sounds are less certain by nature.
Can I use it as an RF spectrum analyzer?
No. Browsers can only reach the audio range through your sound card. Radio frequency work needs dedicated hardware.
Why does my microphone show a spike at 50 or 60 Hz?
That is mains hum picked up by the microphone or its cable. It is the single most common finding on any audio spectrum analyzer.
What audio file formats can I analyse?
Whatever your browser can decode — in practice WAV, MP3, OGG, FLAC, AAC and M4A.