Put it on low while you work. Don't concentrate on it. Every so often the interval surfaces on its own and you notice it, and that noticing is the point.

It's rain with an interval woven through it, quiet enough to sit behind reading, practicing, or writing. You're not doing an exercise. You're spending hours near a sound until it stops being unfamiliar.

These files don't teach you an interval. They reinforce one you're already training awake. If you've never sung a perfect fifth on purpose, start there and come back.

At your desk

Listening awake is not the consolation prize. It's the main event. Your attention is half on it, and that's the condition you want.

Stop once or twice an hour. Sing the interval back. Check yourself against a piano or an app. Then put it back on and forget about it again.

At night

The sleep discs are built for this and the work discs aren't. Use the ones marked Sleep.

The tones are thickest in the first hour. They thin out as the night goes on, because your deep sleep does too. By morning you're mostly hearing rain. The rain holds one level all night, never repeats, and fades to silence across the final thirty minutes instead of stopping. A sleeping brain is a change detector. A sound that stops is a change.

Play it once. Start it as you're getting into bed, so nothing begins or ends after you're under. If it wakes you, stop using it. A cue that wakes you doesn't just fail, it damages the memory it was reactivating.

What's in it

Four discs. Work and sleep, each in a full-length version and a 1:58 version that fits under Apple's sync limit.

The work discs cover twelve intervals, from the seconds through the octave, plus the combined sets. The sleep discs are the perfect fifth, the major third, and the major sixth, each in a louder and a quieter version.

46 files, about 20 GB, and a 15-page manual on how the files are built and what the research does and doesn't support.

Five minutes before bed

Lights off, nothing playing. Sing the interval up and down. Hold the top note after the sound dies. Predict before you check.

Then start the file.