An isoharmonic series is a variation on the harmonic series, where every pitch has been linearly shifted by a rational number:

[math]\displaystyle{ f(n) = c + n }[/math] where [math]\displaystyle{ c }[/math] is rational

So for a:b:c:d:... you have b-a = c-b = d-c = etc.

It is synonymous with the term OS, otonal sequence, which is part of a system of arithmetic and harmonotonic tunings. It is also essentially the series form of an isoharmonic chord.

See also