What an upscaled file is
It's a file converted from a poor source (a 128 kbps MP3, audio ripped from a video) into a better-looking format like 320 kbps MP3, FLAC, or WAV. The file gets bigger and the bitrate goes up, but the highs lost in the original never come back.
On headphones or small speakers, it's hard to hear. On a big system it shows: dull hi-hats and cymbals, no air in the mix. By then it's too late.
Why the spectrogram gives it away
MP3 and other lossy formats throw away high frequencies to save space. The lower the bitrate, the lower the cutoff. Converting to FLAC just copies what's left, so the spectrogram still shows a flat line where the highs were sliced off.
| True source | Spectrogram usually cuts off at |
|---|---|
| 128 kbps MP3 | about 16–17 kHz |
| 192 kbps MP3 | about 18–19 kHz |
| 320 kbps MP3 | about 20 kHz |
| Real FLAC or WAV (44.1 kHz) | can reach close to 22 kHz, no hard wall |
Step by step
- Open the file in any software with a spectrogram.
- Find the densest part, usually the drop.
- Look at the top of the image, where the highs live.
- See a flat wall running across the whole track? Read its frequency and compare it with the table.
- A file labeled FLAC with a wall at 16 kHz almost certainly started life as a 128 kbps MP3.
Cases that fool people
- Old recordings, or masters with the highs rolled off on purpose. They can lack highs and still be the original. An MP3 cutoff is flat and sharp; a natural roll-off fades out gradually.
- Sparse intros and breakdowns. Few highs there is normal. Always check the densest part.
- 48 kHz or 96 kHz files. A higher sample rate only raises the top of the image. If the content inside still stops at 16 kHz, it's still upscaled.
More on reading the image in how to read a spectrogram.
Automatic with TaxonomyDJ
Drag files into the Inspector tab in TaxonomyDJ: it tells you straight which files are upscaled, warns about tracks pushed so loud they're likely to distort, and shows the full-track spectrogram so you can check with your own eyes. Free, and nothing gets added to your library.
Not sure which format to keep? Read MP3 320 vs FLAC vs WAV for DJs.