How to use them

1. Put the file on an audio track in your DAW. Any project sample rate works; 48 kHz matches the file.
2. Insert the plugin you want to test and set it the way you would use it. More drive shows more.
3. Render or bounce the track.
4. Open the result in a spectrogram with a logarithmic frequency scale. Sonic Visualiser and Audacity are free; iZotope RX or your DAW's own spectrogram work too.

What to look for

A distortion makes harmonics: copies of the input at 2, 3, 4 times its frequency and up. On the spectrogram they are lines that rise together with the sweep.

Harmonics that end up above half the sample rate can't exist in a digital signal. If the plugin doesn't oversample or filter enough, they fold back down and come out as frequencies that were never in the input. Those are the lines that go the wrong way: falling while the sweep rises, or zig-zagging across the picture. You also hear them, as whistles that move against the sweep. On a real part that's the fizzy, "digital" edge.

If the plugin has an oversampling setting, render the sweep once at each setting. The falling lines get weaker as the oversampling goes up.

The guitar-range file only sweeps the notes a guitar actually plays, so it shows what you would hear on a real guitar part. The full-range file pushes much harder at the top and finds aliasing that a guitar part would never reach.

The files

Format

WAV, mono, 48 kHz, 24-bit, 21 seconds

Signal

0.5 s of silence, a 20-second logarithmic sine sweep, 0.5 s of silence

Level

−6 dBFS peak

Licence

Free for anything: test your own plugins, use them in reviews, share them. A link back is nice, not required.

I use sweeps like these to check my own pedal models for aliasing: Raging Beaver, Rodenticide and Stockholm Syndrome.