How It Works
When LAME (the standard MP3 encoder) writes a file, it stamps a small LAME/Xing header into the first audio frame recording exactly how the file was made — the encoder version, whether it's CBR, ABR or VBR, the quality preset, the lowpass filter frequency and more. This tool reads that header directly, so it never has to re-encode or upload your file. It's the information the old desktop tool EncSpot used to show, back in the browser.
What the Fields Mean
- Encoder — the program and version, e.g.
LAME 3.100. Files from iTunes, Fraunhofer or older tools may not write a LAME header at all. - Method — CBR (constant bitrate), ABR (average bitrate), or VBR (variable bitrate). VBR files are usually higher quality per megabyte.
- Preset — the quality setting used: V0 (highest VBR) down to V9, an ABR/CBR bitrate, or a named preset.
V0and320 CBRare the top tiers. - Lowpass — the frequency above which the encoder discarded audio. Higher is better: ~20.5 kHz for 320 CBR, ~19 kHz for V0, ~18.5 kHz for V2, ~16 kHz for 128.
- Bitrate — the frame bitrate from the header, plus the true average computed across the whole file.
Why It Matters
On music trackers and archives, the encoder and preset are part of what makes a rip acceptable. This is also the quick way to spot a file that was transcoded up (e.g. a 128 kbps source re-encoded to "320") — pair it with the Spectrogram Analyzer to confirm by eye.
Frequently Asked Questions
Is my file uploaded?
No. Only the first few kilobytes of the file are read in your browser to parse the header. Nothing is sent anywhere.
It says "no LAME header" — what does that mean?
The file wasn't made by LAME, or its header was stripped. iTunes, Fraunhofer, and some older or streaming encoders don't write a LAME tag. The format, bitrate and channel info are still shown.
Can it prove a file wasn't upsampled from a lower bitrate?
Not on its own — the header only records what the last encoder claims. To detect an upscaled transcode, look at the spectrogram for a lowpass cutoff below what the stated bitrate should have.
What does the lowpass frequency tell me?
It's where the encoder cut off high frequencies. A "320 kbps" file with a lowpass down at 16 kHz is a red flag that it was really encoded at a much lower bitrate first.