Check FLAC files for high-frequency rolloff
Drop a FLAC file and look for a sudden drop in high-frequency energy. If the spectrum cuts off sharply at 16–20 kHz, the file may have been transcoded from a lossy source.
Audio Spectrum Viewer
Drop any audio file to see its frequency distribution as a spectrum chart. Useful for spotting high-frequency rolloff patterns typical of lossy compression. This is a visual reference tool — not a quality meter. All analysis runs locally in your browser.
Key features
- Local processing
- No upload required
- Max-hold spectrum display
- Logarithmic frequency axis
- High-frequency rolloff detection
- Sample rate and duration info
How to read the spectrum
The horizontal axis shows frequency on a logarithmic scale from 20 Hz to the Nyquist limit. The vertical axis shows amplitude in dB. A genuine lossless file fills the spectrum close to the Nyquist limit. A sharp drop at a lower frequency — 16 kHz, 18 kHz, or 20 kHz — often indicates lossy compression.
What is max-hold spectrum?
The tool analyzes the file in overlapping windows and keeps the highest amplitude found at each frequency bin. This gives a stable "peak" view rather than a live scrolling display.
Common use cases
Compare MP3 quality settings
Drop two MP3 files encoded at different bitrates and compare where the high-frequency content ends. Higher bitrate MP3 files retain energy up to higher frequencies.
Verify audio before archiving
Check that a file you plan to archive as lossless actually contains the full frequency spectrum before committing to storage.
Frequently asked questions
What does the spectrum tell me?
It shows the distribution of frequency energy in your audio file — this is a visual reference, not an absolute quality meter. A genuine lossless file typically extends close to the Nyquist limit (half the sample rate). A lossy-source file typically shows a sharp cutoff at a lower frequency, but some recordings naturally lack high-frequency content.
What is the Nyquist limit?
The Nyquist limit is half the sample rate. For a 44.1 kHz file, the Nyquist limit is 22.05 kHz. Human hearing extends to roughly 20 kHz, so a genuine lossless 44.1 kHz recording should contain energy up to around 22 kHz.
Is my audio uploaded?
No. All analysis happens locally in your browser using the Web Audio API.
Why is analysis slow for long files?
The tool samples up to 64 evenly spaced windows from the file regardless of duration, so analysis time is roughly the same for short and long files.
About this page
Audio Spectrum Viewer is part of OFPlayer's local-first music workflow. The page is designed to explain the feature, tool, or guide in plain language before you open the interactive app experience.
OFPlayer focuses on personal music collections, browser-based utility tools, WebDAV and Subsonic/Navidrome workflows, privacy-first playback, and lightweight library management. Files stay under your control, and the website avoids account-based lock-in.
Useful next pages from here include Pseudo-Lossless Detector、Audio Metadata Viewer、Loudness Scanner / ReplayGain、GitHub. These internal links help you continue from overview, to setup, to actual playback or tool usage without losing context.