As I find time, I hope to post more about the Rev2-specific considerations when using alternate tunings
1, but since stretched tuning came up on
creativespiral's Voice Component Modeling thread, I thought I'd quickly write up something more general. (As I got going, it ended up not so quick.)
Part 1: Stretched TuningAlthough "piano" stretched tuning was mentioned, there's no single standard for it
2, and few good reasons to apply it to a synth
3. Instead, I have attached a sysex for the slightly and uniformly stretched scale known as
19ED3. It stretches every semitone by about 0.1¢, so that twelfths (a span of 19 semitones, e.g. between C2 and G3) are tuned "perfect". The frequency of the 3rd harmonic of a tone corresponds to a tone perfect 12th above the fundamental, so we're aligning those. In standard
12-Tone Equal Temperament (12TET/12EDO/12ED2), octaves are perfect, but twelfths are about 2¢ flat of perfect.
4The sysex will load 19ED3 tuning into slot 6 on your Rev 2. Enable it through Global parameters.
To really get the [relatively subtle] difference, you should compare the sound of various intervals using a very simple polyphonic patch (e.g. the "init") with the different tunings. Complex patches will likely obscure the differences.
Some Rev2 patches will need to be adjusted to work as intended with alternate tunings; others may never really work, depending on the particular tuning and patch. (Some aspects of this were a surprise to me, so more on that later.)
1Briefly: Alternate tunings are a "nice to have" feature for me, but if I had been expecting the Rev2 to be a
xenharmonic workhorse, I would be posting over in the
Rev2 breakup thread.
2The reason piano tuning is stretched in practice is to account for the inharmonicity of a
piano's sound, caused by the stiffness of the strings and other real-world mechanical influences. Octaves are stretched to sound pure, despite the inharmonicity. The stretching is not uniform across the instrument's range, and every piano is different. Larger pianos like grands generally require less stretching to sound good, and smaller ones like consoles require more. Applying "piano-style" stretching is not really useful unless you really need your synth to be exactly in tune with
one particular piano, across a wide range of its keyboard. (There is a thing called a "Railsback curve" that is an average of observed tunings found in the wild, but it's at best a starting point for tuning a piano that gets polished by ear. Tuning your synth to this might put you more in tune with a given piano, or it might be worse.)
3Synth waveforms are almost completely harmonic, except when we intentionally make them inharmonic with nonlinear functions like ring modulation (or the AUDIO MOD parameter of the Rev2). There may also be some tiny inadverdent inharmonic components introduced by things like
intermodulation distortion in analog circuits. If we're going to use equal nearly-octave-repeating tuning on a synth, it makes more sense to bring some harmonics in line as in 19ED3.
4As every equal-step tuning system is a compromise, getting perfect 12ths results in imperfect octaves. Major thirds will be a little worse than they already are on standard 12-EDO, while fifths will be a little better.
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