Real talk: a significant portion of the WAV and AIFF files in your DJ library are probably MP3s in disguise.
Not because you downloaded from sketchy sources. It happens with record pools, promo packs, even some Beatport purchases when labels upload the wrong master. The file is named .wav, the metadata says WAV, the file size looks plausible but the audio was encoded lossy at some point in the chain and nobody caught it.
What fake lossless actually sounds like
On headphones or a bedroom setup, you might not notice. On a 20kW club system with proper subwoofers and high-frequency horn drivers, the difference is real: a transcoded file lacks air above 16kHz, transients are smeared, and the overall image sounds compressed and flat compared to a genuine lossless master.
The technical reason is the Nyquist limit. A genuine 44.1kHz WAV has audio content up to 22kHz. An MP3 encoded at 320kbps has a hard frequency cutoff — typically at 19kHz or 19.5kHz. An MP3 at 256kbps cuts at around 19kHz. At 128kbps, it cuts at 16kHz. These cutoffs are an artifact of the encoder’s lowpass filter and they’re permanent, re-wrapping the file in a WAV container doesn’t restore what was discarded.
The manual check (and why it doesn’t scale)
The traditional method is Spek (everyone knows it) open a file, look at the spectrogram, check for an abrupt frequency shelf. Works fine for one track. Falls apart at 2,000 tracks.
Spek also hasn’t been updated since 2023, runs through Rosetta on Apple Silicon, and has no batch mode or automatic verdict. For a systematic library audit it’s not practical.
What I’ve been using: Spectro
Spectro is a macOS app built specifically for this use case. Drag a folder in or your entire DJ pool — and it batch-analyzes every file and returns a verdict: Lossless, Transcoded, or Lossy.
The workflow integration is what makes it actually useful day-to-day:
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Finder color tags — files get tagged directly in macOS Finder. Open your library folder and every track is already color-coded. No app to keep open.
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Right-click verdict — right-click any audio file in Finder for an instant result via the context menu extension
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Quick Look plugin — press Space on any file in Finder to see the full spectrogram inline, without opening the app
It’s $39 one-time, no subscription, completely offline. Your audio never touches a server. Free trial covers 100 scans.
Works on WAV, AIFF, FLAC, and MP3. Detects transcodes regardless of container format — so a fake lossless FLAC gets caught too.
Practical workflow
My current process: new tracks go into a staging folder before they hit the main library. Spectro scans the folder, Finder tags show green (lossless) or red (transcoded) immediately. Anything red either goes back to the source for a replacement or gets downgraded to the MP3 folder where it belongs. Takes about 30 seconds per batch.
For the initial audit of an existing library I ran it on 3,400 files. Took under 5 minutes. Found 214 transcoded files, mostly older promos and a handful from a record pool I used years ago.