Hermode Tuning

One of my strongest areas of musical interest is microtonality. Many musicians think that word refers to intervals that are smaller than a semitone, but

One of my strongest areas of musical interest is microtonality. Many musicians think that word refers to intervals that are smaller than a semitone, but that's only part of the story. More important for Western music, microtonality can be applied to the familiar intervals by retuning them a few cents away from their equal-tempered prison and toward purer just intonation. In fact, wind and string players in orchestras and chamber ensembles retune constantly, “shading” notes up or down to bring them more in tune with the other notes being played at the same time.

It has long been a dream of mine to have a system that automatically retunes synthesizer notes in the same manner. Now, such a system is finally on the verge of becoming widely available. Developed by German musician Werner Mohrlok and his computer-programmer son, Herwig, the system is called Hermode Tuning, or HMT (www.hermode.com). To hear what this system can do, listen to the excellent audio examples on the Hermode Web site.

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HMT has a database of predefined intervals and chords of up to six notes, which allows it to quickly identify intervals and chords as they are played. It then retunes the notes to bring them closer to pure just intonation. In some modes, each chord is analyzed only for the intervals it has, but in at least one mode, the harmonic center is also taken into account by keeping track of the last ten chords played. In that case, chords near the harmonic center are closer to pure than chords that are more distant, much like the well-tempered tuning systems of the baroque era. Unlike those systems, however, HMT is dynamic, shifting the temperament according to the harmonic center.

One of the most amazing aspects of HMT is its compatibility with equal temperament, which is crucial when wind and string instruments play with a fixed-intonation instrument, such as a piano or harpsichord. Instead of identifying the root of each chord and retuning the other notes while leaving the root at its equal-tempered pitch, all notes are adjusted so that the average detuning from their equal-tempered pitches is as close to zero as possible.

One problem that arises in any such system is pitch drift. As notes are retuned, they are then used to calculate the pitches of the next notes, and so on, which can eventually lead to notes that are far from the original pitch center. Another problem is the need to retune notes that are common from one chord to the next because they occupy different positions in each chord. Depending on the pitches and timbres being played, changes of as little as three or four cents can be heard.

To overcome those problems, HMT's equal-temperament reference (that is, the set of all 12 equal-tempered pitches) is shifted up or down as needed to minimize pitch drift and the amount by which notes common to sequential chords must be retuned. To keep things from getting out of hand, the reference is shifted by no more than 15 cents in either direction from the default level, and the system strives to return to the default level whenever possible. As you can see in Fig. 1, the top example requires no reference shifting because it stays squarely in one key center, while the bottom example shifts the reference because it contains wide-ranging modulations.

HMT is currently available in the latest operating software (OS6) for Access Virus synths as well as Apple's Logic Pro 7, and it's expected to be implemented in software synths from Native Instruments and others. I'm excited about this technology, which finally allows synthesized music to play in tune like never before.