Frequency Spectrum
Frequency Bands
About FFT Spectrum Analysis
The Fast Fourier Transform (FFT) converts audio from the time domain into the frequency domain, showing which frequencies are present in the sound and their relative intensities. This is fundamental to audio engineering, music production, and acoustic analysis.
Understanding the Display
- X-axis (horizontal): Frequency in Hz (logarithmic scale by default)
- Y-axis (vertical): Amplitude/intensity in decibels (dB)
- Bar height: How loud that frequency band is
- Peak markers: Show the loudest frequencies in real-time
FFT Size Explained
| FFT Size | Frequency Resolution | Time Resolution | Best For |
|---|---|---|---|
| 256 | ~172 Hz | ~6 ms | Fast transients, percussion |
| 1024 | ~43 Hz | ~23 ms | General analysis |
| 2048 | ~22 Hz | ~46 ms | Balanced (default) |
| 4096 | ~11 Hz | ~93 ms | Low frequency detail |
| 8192 | ~5 Hz | ~186 ms | Precise pitch analysis |
Common Frequency Ranges
| Range | Frequencies | Examples |
|---|---|---|
| Sub-bass | 20-60 Hz | Kick drums, bass drops |
| Bass | 60-250 Hz | Bass guitar, male voice fundamentals |
| Low Midrange | 250-500 Hz | Body of instruments, warmth |
| Midrange | 500-2000 Hz | Speech clarity, most instruments |
| Upper Midrange | 2-4 kHz | Presence, intelligibility |
| Presence | 4-6 kHz | Clarity, definition |
| Brilliance | 6-20 kHz | Air, cymbals, "sparkle" |
Practical Uses
- Music Production: Identify frequency clashes, check mix balance
- Acoustic Analysis: Detect room resonances, noise sources
- Voice Training: Visualize vocal harmonics and pitch
- Audio Troubleshooting: Find hum, buzz, or unwanted noise
- Speaker Testing: Check frequency response
Frequently Asked Questions
What is the difference between FFT and a regular spectrum analyzer?
FFT is the algorithm used to compute the frequency spectrum. It efficiently breaks down complex audio into individual frequency components. Most digital spectrum analyzers use FFT as their underlying technology.
Why does higher FFT size mean better frequency resolution but worse time resolution?
This is due to the Heisenberg uncertainty principle in signal processing. A larger FFT window captures more cycles of low frequencies (better frequency detail) but responds slower to changes. A smaller window updates faster but can't distinguish closely-spaced frequencies.
Why use logarithmic scale instead of linear?
Human hearing perceives pitch logarithmically—we hear equal musical intervals (octaves) as equal pitch changes, not equal Hz differences. A logarithmic display matches this perception, giving equal visual space to each octave.
What causes the background noise floor?
The noise floor comes from microphone self-noise, ambient room noise, and quantization noise from analog-to-digital conversion. Good microphones in quiet rooms show lower noise floors.
Privacy & Limitations
- All calculations run entirely in your browser -- nothing is sent to any server.
- Results are estimates and may vary based on actual conditions.
Related Tools
- Metronome -- Simple metronome with adjustable BPM and time signatures
- White Noise Generator -- Generate white, pink, and brown noise for focus or relaxation
- Speaker Frequency Sweep -- Test speakers with a frequency sweep from 20Hz to 20kHz
- Audio Latency Tester -- Measure audio input/output latency in milliseconds
Related Tools
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Drag and drop an .opus file to view its embedded metadata and transcription
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Metronome
Simple metronome with adjustable BPM and time signatures
Frequency to Note Converter
Convert frequency (Hz) to musical note name and cents offset
Audio Timer
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White Noise Generator
Generate white, pink, and brown noise for focus or relaxation
FFT Spectrum Viewer FAQ
What is FFT Spectrum Viewer?
FFT Spectrum Viewer is a free audio tool that helps you Real-time frequency spectrum analyzer with bar graph display.
How do I use FFT Spectrum Viewer?
Enter your input values, review the calculated output, and adjust inputs until you reach the result you need. The result updates in your browser.
Is FFT Spectrum Viewer private?
Yes. Calculations run locally in your browser. Inputs are not uploaded to a server by default, and refreshing the page clears session data.
Does FFT Spectrum Viewer require an account or installation?
No. You can use this tool directly in your browser without sign-up or software installation.
How accurate are results from FFT Spectrum Viewer?
This tool applies standard formulas or deterministic processing logic for estimates. For medical, legal, tax, or investment decisions, verify with a qualified professional.
Can I save or share outputs from FFT Spectrum Viewer?
You can bookmark this page and copy outputs manually. Results are not persisted in your account and are typically not embedded in the URL.