Re: Microtonal support

[Graham Breed]

2008/12/22 Graham Percival <address@hidden>:
> On Mon, Dec 22, 2008 at 12:09:10PM +0800, Graham Breed wrote:
>> I've been investigating the new pitch model with Hans.  It is, in
>> fact, better than either of us thought but some of that isn't
>> documented.  So pay attention.
>
> Great!  I'm not certain if any of the doc team has much experience
> with microtones -- let's just assume that they don't.  Could you
> propose some changes to the docs to make this more clear?  Ideally
> it would look something like this:

I can have a look.  Of course, the average reader isn't going to have
experience with microtones either so we have to make sure they can
still understand it as well.

I think it's valid if the documentation on microtonal tweaks says that
certain assumptions made elsewhere are not always valid.
Microtonalists will go straight to the microtonal section anyway.
(Except that right now I've lost it.)

> Even if your proposed changes need a bit of modification to fit
> into the existing docs, having a concrete proposal will help us a
> lot.  Again, please assume that the doc team knows nothing about
> microtones -- this will help us avoid misunderstandings.

Probably a new example in the microtonal section for meantones.
Meantone temperaments in general are a very important set of tunings.
They also show up the general case of retuning with no reference to
conventional equal temperament.

Another thing -- changing the number of steps to the octave needn't be
microtonal.  The same feature can give us dodecaphonic notations.  One
I know about from Schoenberg will at least be a challenge because it
has ledger lines in the middle of the staff.  But I could rustle up
something like Erv Wilson's idea.

>> First, alterations are specified in terms of what the documentation
>> vaguely calls "whole tones".  They are specifically intervals of 200
>> cents or steps of 6 note equal temperament.  For many tunings the size
>> of a tone or double sharp will not have this value.
>
> Could you identify specific place(s) where this should be stated,
> and/or reword the sentences to avoid the vague "whole tones" term?

Notation Reference B.15 and Internals Reference 4. Scheme Functions

The current discription of ly:make-pitch is

"octave is specified by an integer, zero for the octave containing
middle C. note is a number from 0 to 6, with 0 corresponding to pitch
C and 6 corresponding to pitch B. alter is a rational number of whole
tones for alteration."

Now, what do we say instead of 0 to 6?  It's really from 0 to one less
than the number of notes in the default scale that's active at the
time ly:make-pitch is called.  One option is to leave that out
altogether.  Anyway, how about

"octave is specified by an integer, zero for the octave containing
middle C. note is a number indexing the global default scale, with 0
corresponding to pitch C and 6 usually corresponding to pitch B. alter
is a rational number of 200 cent whole tones for alteration."

--

Not far below that below that, ly:make-scale can be

Create a scale. The argument is a vector of rational numbers, each of
which represents the number of 200 cent tones of a pitch above the
tonic.

--

That leads us to ly:set-default-scale scale which is currently explained as

    Set the global default scale.

So what is this "global default scale"?  I don't know what it's there
for because I didn't put it there.  But I know what it can be used
for, so lets try

    Set the global default scale. This determines the tuning of
pitches with no accidentals or key signatures.  The first pitch is C.
Alterations are calculated relative to this scale.  The number of
pitches in this scale determines the number of scale steps that make
up an octave.  Usually the 7 note major scale.

--

ly:default-scale

Very terse description again and I haven't found a context where it
does anything.  It's used internally but always seems to return #f in
a score even when setting that default scale still changes something.

--

Notation Reference 3.5.3 What goes into the MIDI output?

Still says Quarter tones.  Should be Microtones.

Maybe "microtonal chords" could be listed as unsupported.

--

Lilpond snippets: Pitches

under Non-traditional key signatures

I'm afraid the SHARP, FLAT, etc. constants won't work in general
because they aren't constant.  I don't know the solution to this
because they're obviously there for a reason.  But at least there has
to be another paragraph like


For microtonal scales where a "sharp" is not 100 cents, alter refers
to the alteration as a proportion of a 200 cent whole tone.


But the best thing is to fix the \key version and suggest that instead
because it changes with the tuning.

--

How about the Music Glossary?  I"ll list some changes but you're free
to reject them and say I should find something else to do with my time
;-)

3. Pitch names

Lists some enharmonic equivalences, like f-flat = e, but not all of
them.  With Lilypond's pitch model even if they sound the same they
aren't the same.

--

 1.154 interval

The augmented fourth and the diminished fifth are identical (or
enharmonic) and are called tritonus because they consist of three
whole tones.

Should be "identical on a twelve note scale (or enharmonic)".
(They're always enharmonically related.)

--

1.7 accidental

No need to be pedantic about this but I'm not sure about the (a whole
tone) remarks.  The two semitones that add up to a whole tone (as in C
to D) are generally different sizes and not equal to a double sharp.
Whereas it might not do any harm I think the reader can guess what
"two semitones" means anyway.

--

1.325 whole tone

Confused.  First says a major second, then two steps on a piano
keyboard.  Whatever you call a "whole tone" a major second is always
one step on the staff but your piano keyboard could give you a
diminished third (C sharp to E flat) as far as it distinguishes such
things.  The "whole tone scale" will include diminished thirds.

The "whole tone" that two semitone accidentals add up to is neither of
these.  It's an augmented prime.


                         t'other Graham