Quarter Tone Generator

Choose four notes with their octaves, or load a chord and change the notes you like.
Read the new scale in the table, with the quarter-tone steps, cents and frequencies. Open “Show the ring modulation steps” to see how it was built.
Play the chord (set the time between notes, 0 for all together) and the scale up, down, or up and down.
Download an .scl file for your synth or sampler, save a CSV, or copy the scale as text.

How do you generate a quarter-tone scale from a chord using ring modulation?

Ring modulation of two sine waves gives their sum and their difference. Chaining three ring modulators over the four notes of a chord gives eight frequencies, |f1 ± f2 ± f3 ± f4|. Fold them into one octave, transpose them so the lowest sits on the lowest note of the chord, round each to the nearest quarter tone (50 cents) and merge the duplicates: you get a new scale of five to eight notes. A C major seventh (C4 E4 G4 B4) gives seven notes, at 0, 150, 400, 450, 550, 700 and 1000 cents above C4. This free generator does the calculation, plays the scale up and down and exports it as an .scl file.

What is a quarter-tone scale, and what is ring modulation?

A quarter tone is half a semitone, so an octave has 24 steps instead of 12: the notes in between the keys of a piano. Ring modulation multiplies two sounds, and the result contains their sum and their difference, which are rarely notes of the piano. This tool applies that idea to the notes of a chord, and brings the results into one octave and rounds them to quarter tones. The scale that comes out keeps something of the harmony of the chord you started from, but sounds new.