# Audio Spectrogram Online - STFT Frequency Analysis with Log/Linear Axis, Export PNG

> Free online spectrogram generator: see time, frequency and level from a Hann-windowed STFT, with FFT size, log axis, dB range and colour maps. Exports PNG.

- URL: https://qilingtools.com/en/audio/spectrogram
- Category: Audio Tools (https://qilingtools.com/en/audio)
- Tags: [Audio](https://qilingtools.com/en/tags/audio), [Physics](https://qilingtools.com/en/tags/physics), [Charts & Visualization](https://qilingtools.com/en/tags/chart)
- Last updated: 2026-10-26
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

A spectrogram draws sound as an image: time runs left to right, frequency bottom to top, and brighter colors mean more energy at that moment and pitch. It is the go-to way to spot “fake lossless” music (a hard cutoff at 16 kHz means it was converted from MP3), study vocal and instrument harmonics, find hum, feedback or noise frequencies in a recording, analyze birdsong and speech, or make striking artwork from audio. This tool decodes the file with Web Audio and computes a Hann-windowed short-time Fourier transform with a radix-2 FFT written in JavaScript, processed in chunks with a progress bar so long files stay responsive. Choose an FFT size from 512 to 8192 and 50–87.5% overlap, a logarithmic or linear frequency axis with custom limits, the dB floor and ceiling that set the contrast, and Magma, Viridis, Inferno or grayscale colors on a dark or light background. Click anywhere to read the time, frequency (with the nearest musical note, such as A4) and level in dB, or analyze just a segment to zoom in. Export a PNG with time axis, frequency axis and color bar.

## How to use

1. Upload an audio file (MP3, WAV, FLAC, M4A, OGG…) or a video — it is decoded and plotted automatically
2. Adjust FFT size, frequency axis, dB range and colors; click the image to read time / frequency / dB
3. Optionally set a start and end time to analyze one section, then click Export PNG

## Features

- Pure in-browser STFT: radix-2 FFT with Hann window, chunked with progress
- FFT size 512–8192 with 50% / 75% / 87.5% overlap
- Logarithmic or linear frequency axis with min / max limits
- Adjustable dB range; Magma, Viridis, Inferno and grayscale maps
- Click to read time, frequency, musical note and dB
- Analyze mix, left, right or side (L−R) channel
- Analyze a selected segment for finer time detail
- Export a labeled PNG up to 3840 px wide

## FAQ

### How can a spectrogram tell whether a FLAC is really lossless?

Load the file with the highest frequency set to “All”. Genuine CD-quality audio usually has content reaching about 20 kHz. A clean, flat cutoff around 16 kHz or 19 kHz with near-black above it is the typical fingerprint of a file transcoded from MP3 or AAC. Some recordings are naturally dull, so compare several tracks before drawing conclusions.

### Which FFT size should I pick?

Bigger windows resolve pitch more finely but blur timing; smaller ones show sharp transients but smear frequency. Use 512–1024 for speech and drums, 2048–4096 for musical pitch and harmonics, and 8192 for low-frequency detail. More overlap gives a smoother image at the cost of extra computation.

### Why does the axis go up to 24,000 Hz?

Browsers usually decode audio at 48 kHz, so the highest representable frequency (the Nyquist frequency) is 24 kHz. A 44.1 kHz file will be empty above 22.05 kHz, which is expected. Use the Highest frequency option (20k, 16k…) to show only the useful range.

### Is my audio uploaded? Is it free?

Nothing is uploaded — decoding and the spectrum computation run entirely in your browser and are discarded when you close the page. The tool is free, with no sign-up, no limits and no watermark.

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