FFT Spectrum Analyzer

FFT Spectrum Analyzer is a browser-based audio analysis tool that shows the frequency content of live microphone input in real time. It helps visitors see how sound energy is distributed from low bass frequencies through the upper range of human hearing.

What the App Does

The app listens to microphone input, performs a Fast Fourier Transform (FFT), and displays the result as a live spectrum graph. The horizontal axis shows frequency from 20 Hz to 20 kHz on a logarithmic scale, which matches how audio engineers and musicians commonly view sound. The vertical axis shows amplitude in dBFS, from the selected noise floor up to 0 dBFS.

This makes it useful for observing tones, room noise, speech, music, speaker output, hum, feedback, and other audio signals in real time.

Main Features

• Live microphone input: The analyzer requests microphone permission from the browser and processes the audio locally in the user's browser tab.
• FFT spectrum display: Converts incoming sound into frequency-domain data so users can see which frequencies are present.
• Log-scaled frequency axis: Displays 20 Hz to 20 kHz with meaningful frequency labels such as 20, 50, 100, 200, 500, 1k, 2k, 5k, 10k, and 20k Hz.
• dB amplitude scale: Shows signal level using a dBFS-style vertical scale with grid lines for easier reading.
• Gradient-filled spectrum: Uses deep blue, cyan, green, yellow, and red colors to make intensity and frequency regions easy to distinguish.
• Cyan trace line: Draws a clear real-time line over the spectrum for precise visual tracking.
• Peak hold dots: Orange dots show recent peak levels across the frequency range and decay over time.
• Adjustable FFT size: Users can choose from 256 to 16384 points while the analyzer is running.
• Smoothing control: Lets users choose whether the display reacts quickly or moves more steadily.
• Peak decay control: Controls how quickly the orange peak-hold indicators fall back down.
• Selectable dB floor: Lets users choose a display floor from -60 dB to -120 dB depending on the signal level and noise environment.
• Live technical readouts: The footer shows FFT size, frequency resolution, bin count, sample rate, and the current peak frequency.

How to Use It

1. Open the FFT Spectrum Analyzer page in a modern browser.
2. Click Start Mic.
3. When the browser asks for permission, allow microphone access.
4. Play a sound, speak into the microphone, or measure sound from a nearby speaker or environment.
5. Watch the live spectrum display. Low frequencies appear on the left, high frequencies appear on the right, and louder signals rise higher on the graph.
6. Use FFT Size to adjust the tradeoff between frequency detail and response speed. Larger FFT sizes provide finer frequency resolution, while smaller sizes respond faster.
7. Use Smoothing to make the trace steadier or more responsive.
8. Use Peak Decay to control how long the orange peak indicators remain visible.
9. Use dB Floor to adjust the visible noise floor for quiet or loud environments.

Understanding the Display

Frequency axis: The bottom axis is logarithmic from 20 Hz to 20 kHz. This gives more visual space to the lower and middle frequencies, where many musical and room-acoustic details are easier to inspect.

Amplitude axis: The left axis shows level in dBFS. Values closer to 0 dB are louder. Lower values represent quieter sound or background noise.

Peak frequency: The footer reports the strongest frequency currently detected in the measured range.

Peak hold: Orange dots show recent maximum levels and slowly decay, making short peaks easier to notice.

Privacy and Browser Requirements

The microphone audio is analyzed locally in the browser. The app does not need to upload audio to a server for the spectrum display to work.

Microphone access requires browser permission. Some browsers may require the page to be served from HTTPS or from localhost before microphone access is allowed.

Suggested website note: For best results, use headphones or measure in a quiet environment. Browser microphone processing, device microphones, and room acoustics can affect what appears on the spectrum.