The short answer
Spek is a free, open-source tool that does one job: it draws the spectrogram of an audio file. You look at the image and decide for yourself whether the file was upscaled.
If you only check a file now and then and you're comfortable reading spectrograms, Spek is all you need. If you just downloaded a whole folder and want to know right away which files have problems, the Inspector tab in Taxonomy DJ gets there faster: drop the whole batch in, every file gets a green, yellow, or red finding, and the full-track spectrogram is still there so you can double-check with your own eyes.
What Spek does well
Spek suits quick file checks because it's simple and clear:
- Free and open source (GPL-3.0 license), running on Windows, macOS, and Linux.
- One job, done cleanly: open a file and you get the spectrogram of the whole track.
- Reads many formats, because Spek decodes audio with the FFmpeg libraries.
- Adjustable rendering: change the palette, the DFT window size and function, and the upper and lower limits of the dynamic range.
- Switches channels and audio streams in files that have more than one.
- Saves the spectrogram as an image, handy when you want someone else to take a look.
Spek doesn't give a verdict on whether a file is genuine. It hands you the picture, and the reading is up to you.
What Taxonomy DJ adds beyond the spectrogram
The Inspector tab has a full-track spectrogram too, but it also does the reading for you:
- Drop many files at once. Each file gets a row; select a row to see that file.
- Flags upscaled files: WAV, FLAC, or 320 kbps MP3 files converted from a poor source are clearly marked.
- Clipping warnings: tracks pushed too loud, likely to distort at their loudest moments, are flagged.
- Color-coded findings: green is fine, yellow is worth a look, red is a problem.
- A spectrogram you can zoom on both axes, switch between a linear and a log frequency axis, change the dB floor, and hover to read seconds, Hz, and dB.
- File details alongside: format, bitrate, sample rate, BPM, key, and loudness (LUFS). Loudness is compared to your own library, so outliers stand out.
- Listen right away: double-click to play, with the waveform, spectrum, and EQ in the player.
The Inspector adds nothing to your library. To keep the results, right-click ▸ File details.
Side by side
| Spek | Taxonomy DJ | |
|---|---|---|
| Platforms | Windows, macOS, Linux | Mac (Apple chip, Intel), Windows |
| Price | Free, open source | Inspector free on every plan |
| Full-track spectrogram | Yes | Yes, zoom on both axes |
| Files at a time | One file per window | Many files in one go |
| Flags upscaled files | No, you read the image | Yes |
| Clipping warning | No | Yes |
| BPM, key, loudness (LUFS) | No | Yes |
| Save the spectrogram as an image | Yes | No |
| Formats | Many, decoded with FFmpeg | MP3, WAV, FLAC, AIFF |
The table lists only what we could check on Spek's official pages and documentation at the time of writing (October 2026).
When to keep Spek
- You use Linux. Taxonomy DJ is available for Mac and Windows only.
- Your files aren't just MP3, WAV, FLAC, and AIFF. Spek reads more formats.
- You need to export the spectrogram to post on a forum or send to a group chat.
- You like tuning the DFT window and palette to look at files your own way.
- You want a small, open-source tool that opens and shows, and nothing more.
When Taxonomy DJ fits better
- You just downloaded a whole folder and want to find the problem files without opening each one.
- You're not used to reading spectrograms yet and want a clear finding first, with the image there to confirm.
- You also want to know which tracks are likely to distort, and which ones are much louder or quieter than the rest of your library.
- Once the check is done, you want to keep going in the same app: BPM and key detection, duplicate cleanup, tag editing, and classifying music by your own labels.
FAQ
Is Spek available for Mac?
Yes. Spek is free for Windows, macOS, and Linux. Taxonomy DJ has versions for Apple-chip Macs, Intel Macs (macOS 15 or later), and Windows 10 and 11.
Is there a free alternative to Spek?
Yes. The Inspector tab in Taxonomy DJ is free on every plan: spectrogram, upscaling and clipping findings, BPM, key, and loudness. Only predicted labels need Premium.
If you also need to edit audio, Audacity has a spectrogram view as well, and it's free and open source.
How do I tell a fake FLAC from its spectrogram?
Look for a flat wall running across the top of the image during the densest part of the track. A file that started as a 128 kbps MP3 usually cuts off around 16 kHz, a 320 kbps MP3 around 20 kHz, while a genuine FLAC reaches close to 22 kHz with no hard wall. The full walkthrough is in how to spot a fake FLAC.
Does the Inspector add files to my library?
No. The Inspector is for looking only; close the session and it's gone, with nothing added to your library. To keep the results, right-click ▸ File details.
Try Taxonomy DJ
- Drag audio files into the Inspector tab, or click Choose files. A whole batch works too.
- Select a file to see its findings, file details, and spectrogram.
- Click the zoom icon at the end of the SPECTRUM heading row to look closely, and hover over the image to read the values.
- Want to keep the results? Right-click ▸ File details.
Every step above is free. Download Taxonomy DJ and try it on your latest downloads.
Read next: how to read a spectrogram · how to check for a real 320 kbps MP3.
Spek is a trademark of its respective owner. Taxonomy DJ is not affiliated with Spek.