Spectrum — a modern take on Spek that tells you whether your "FLAC" is really a laundered MP3, made with Opus 5

Direct download (Windows x64, portable, no installer): filedn.eu/lwGY1UhAsUam9BITOnlFrzV/Spectrum.zip Spek draws you a spectrogram and leaves you to judge the cutoff by eye. Spectrum measures the cutoff, measures how sharp it is, compares it against what the declared format should look like, and tells you what it found — a 320 kbps MP3 that was really upscaled from 128, or a FLAC that is a laundered MP3. What it does Grades every file — excellent / good / fair / suspicious / poor, with a sentence saying why. Catches lossy-to-lossless transcodes, upsampled files (44.1 → 96 kHz with nothing new up there), and 16-bit padded into a 24-bit container. Where the cutoff carries bitrate information it estimates the source bitrate; for Opus it tells you it can't, instead of guessing. Shows its work — an optional overlay draws the level envelope and the exact threshold the cutoff was decided against, so you can check the verdict instead of trusting it. Batch mode — point it at a folder, sort the table by verdict, bad files first. Modern spectrogram — perceptually uniform palettes (Magma, Inferno, Viridis) instead of the old rainbow ramp, so magnitude reads as brightness. Spek's classic palette is in there if that's what your eyes know. Linear or log axis, selectable FFT size, adjustable range, crosshair readout, peak/RMS/crest/clipping. A CLI with JSON output and PNG rendering, if you want to script a library scan. Anything ffmpeg decodes: FLAC, MP3, AAC/M4A, Opus, Vorbis, ALAC, WavPack, WAV, and the rest. What it can't do: cutoff analysis finds band limiting, not quantisation damage. A transcode from a high-bitrate lossy source that kept its full bandwidth won't be caught. Notes One file, ~100 MB. ffmpeg is bundled inside the exe — nothing to install, nothing to put on PATH. Unpacks to %LOCALAPPDATA%\Spectrum on first run; delete it any time. Not code-signed, so SmartScreen will warn you: "More info" → "Run anyway". * Spectrum is MIT. Bundles ffmpeg (LGPL v3) from the BtbN builds, unmodified and run as a separate process; sources at ffmpeg.org. LICENSE and THIRD-PARTY-NOTICES are in the zip, and you can drop your own ffmpeg.exe next to Spectrum.exe to override the bundled one. Happy to hear what it gets wrong — especially false positives on genuinely band-limited old masters, which is the hardest case to get right.