SPECTRUM
Audio spectrum and quality analysis for Windows
===============================================

Spek shows 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.


GETTING STARTED
---------------
Double-click Spectrum.exe. There is nothing to install.

Windows will show a SmartScreen warning the first time, because the executable is not
code-signed: click "More info", then "Run anyway".

The first launch takes a second or two longer than the rest. Spectrum carries ffmpeg
inside the executable and unpacks it to %LOCALAPPDATA%\Spectrum\ffmpeg once.

Drop files or a folder onto the window - or onto the .exe itself - to analyse them.
Spectrum reads anything ffmpeg can decode: FLAC, MP3, AAC/M4A, Opus, Vorbis, ALAC,
WavPack, WAV, and the rest.


WHAT IT LOOKS FOR
-----------------
Every file gets a grade and a sentence explaining it:

  excellent    full-bandwidth content consistent with the declared format
  good         a cutoff where the format says there should be one
  fair         band-limited, but gradually - an old or deliberately filtered master
  suspicious   the label and the measurement do not agree
  poor         a lossless container holding something that was lossy

It 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; where it does not - Opus, for
instance - it says so instead of guessing.

The optional profile overlay draws the level envelope and the exact threshold the
cutoff was decided against, so a verdict is something you can check rather than take
on trust.

What it cannot do: cutoff analysis detects band limiting, not quantisation damage. A
file transcoded from a high-bitrate lossy source that kept its full bandwidth will not
be caught.


REQUIREMENTS
------------
Windows 10 or later, 64-bit. Nothing else - no .NET runtime, no ffmpeg install.

Spectrum writes nothing to the registry and nothing to Program Files. It can be run
from a USB stick. The only thing it leaves behind is the unpacked ffmpeg in
%LOCALAPPDATA%\Spectrum, which is safe to delete.


USING YOUR OWN FFMPEG
---------------------
The bundled copy is a convenience, not a requirement. Put ffmpeg.exe and ffprobe.exe
in the folder next to Spectrum.exe, or point the SPECTRUM_FFMPEG environment variable
at a folder holding them, and Spectrum will use yours instead.


LICENCE
-------
Spectrum is MIT licensed - see LICENSE.

It bundles FFmpeg under the GNU Lesser General Public License version 3, redistributed
unmodified and run as a separate process. See THIRD-PARTY-NOTICES.txt for the full
list of components, and licenses/ffmpeg-LICENSE.txt for the LGPL text. FFmpeg sources
are at https://ffmpeg.org/download.html.
