Keyboard Labels

Hebdomad is a Xenharmonic Musical Instrument

Play Hebdomad on the home row of your keyboard using asdf and jkl; for notes, and g and h to control the volume.

Xenharmonic What?

In Western music, we use a tuning system that divides an octave into twelve equal parts to define twelve tones. Hebdomad is made for exploring the spaces between these twelve tones. These spaces hold the world of Xenharmonic music, and here you will find sonic mysteries old and new!

Hebdomad is built for heptatonic scales, which are scales with seven notes to an octave. You can view the scale degrees by clicking the Deg button in the Controls tab.


Hebdomad uses sound waves that are shaped and sculpted in the Controls tab to produce its voice.

Select a base waveform for Hebdomad from the Oscillator section. The sine wave is the most pure and is great for hearing a new tuning. The other waveforms are richer and sound best when shaped with the Amplitude Envelope and Low-Pass Filter.

The Amplitude Envelope shapes the body and character of Hebdomad's voice. An amplitude envelope controls how loud a note is when you press a key, after you let go of the key, and the time inbetween. You can think of the Attack, Decay, Sustain and Release as phases in the journey of a note.

Attack defines how quickly the sound grows, Sustain sets the volume of the held note, and Release defines how quickly the sound fades away when you release the key. Decay allows the note to fade a little before reaching its sustain level. Each of these phases is measured in milliseconds.

The Low-pass Filter (LPF) removes some of the higher frequencies from a sound. This doesn't matter much when using the sine wave, but it can soften the sound and give it a different character when using the other waveforms.

The Amp controls the volume of the instrument. You can also control the volume with g and h on your keyboard.

The Keyboard Labels change the labels on the keys: Key for keyboard characters, Deg for scale degrees, and Cent to display the current tuning. The scale degrees are numbered 1 to 8, and can be switched to display 0 to 7 by selecting Deg a second time.


In the Retune tab, you can select scales from three main categories of tunings: Just, Trivalent Just and Equal Temperaments.

Just and Trivalent Just tunings use whole number ratios to create range of beautiful and rich scales. The Harmonic and Subharmonic Division of Octave tunings divide the octave based on the harmonic series. The theory behind the Trivalent Just tunings is fascinating but is far too much to get into here. Try starting with the 5/4, 3/2 Lydian scale or the 13/11, 3/2 Dorian scale, and when you are feeling adventurous try the others.

Equal Temperaments are the scales you are probably most used to. Here you can find the 12-tone Equal Temperament Major, Minor and Harmonic Minor scales. You can also try the 7-tone Equal Temperament which sounds really different!

Each scale gives a breakdown of its steps represented in cents and ratios for the just tunings. Cents are a measure based on the 12-tone Equal Temperament system, where each step between two consecutive tones is 100 cents. The just tunings use whole number frequency ratios to divide an octave into intervals. Notice how their cent values differ slightly or significantly from the 12-tone Equal Temperament values.


Define custom tunings and set the base frequency in the Custom tab.

Hebdomad's keyboard can be set using the Custom Tuning inputs, which accept positive, negative and decimal values. The Base Frequency input defines the frequency at 0 cents. Each key on the keyboard is offset in cents from the base frequency.

Explore and experiment! The whole point of Hebdomad is to try out new tunings or to make up your own. One fun tuning to try is a quarter-tone scale: 0|50|100|150|200|250|300|350. Try playing this scale quickly up and down the keyboard while using the sine wave.

The best way to explore new tunings is with the free Scala tuning software and its enormous archive of scales. In the contents listing for the archive, heptatonic scales have a size value of 7. To find the tuning in cents for a scale, Open a .scl file from the archive and select Show. The third column displays the tuning in cents.

Thank You for Trying Hebdomad!

Hebdomad is currently v0.7 and more tunings and features will be added with time. The source code is on my GitHub page. If you have any questions, feedback, or recommendations, please contact me on my main site.

Xenharmonic music is a vast garden of study and exploration. For those inclined, I recommend a visit to the Xenharmonic wiki. In addition, Xen-Arts is a great resource for musicians who want to produce tracks using alternate tuning systems. Xen-Arts distributes an excellent set of VSTi for free and blogs on tuning in music technology.

Welcome to Hebodmad

Hebodmad fits better in a larger browser window and is not meant for mobile devices.

Welcome to Hebdomad

Play Hebdomad on the home row of your keyboard using asdf and jkl; for notes, and g and h to control the volume. See the guide for more information.