Re: [frogs] Re: Lilypond's internal pitch representation and microtonal notation

[Wols Lists <antlists@xxxxxxxxxxxxxxx>]

 On 20/09/10 19:57, Carl Sorensen wrote:
> On 9/20/10 10:00 AM, "Wols Lists" <antlists@xxxxxxxxxxxxxxx> wrote:
>
>>  On 20/09/10 14:41, Hans Aberg wrote:
>>>> As a related issue, have you considered how (different kinds of)
>>>> transposition would be handled in your pitch scheme?
>>>
>>> This is much simpler: the linear combinations are vectors that you
>>> just add. For example, if a, b, c, ... are represented by 0, M, m+M,
>>> ..., and you want to transpose from b to c, just add m. A sharp is M-m
>>> and a flat m-M. If you want transpose from a note x to a note y, just
>>> add y - x.
>> What you've missed (and I need to address) is "what is x?".
>>
>> Let's say I want to transpose up three semitones. That's probably easy,
>> it's a minor third, but it could be an augmented second. So, trying to
>> remember the pitch class, is it (0,2,sharp) or (0,3,flat)? And, for your
>> example of that, I've currently got a modified chord engraver on the
>> frogs list that's added a guitar capo property. All the engraver is told
>> is how many semitones to transpose, and it's got to sort out all the keys!
> In reading this, I may have a suggestion for how to handle your
> transposition problem with the capo.
>
> What if instead of giving the fret number for placing the capo, you gave the
> sounding key and the fretboard (capo) key.  Then you could transpose the
> sounding chords by the difference in the keys, and you'd get the chord names
> you want.  And you could calulate the capo fret based on the difference in
> the keys as well.
>
> The challenge we had in the past was not enough information to do the right
> thing, because we were looking at just the fret count.  Then, starting from
> the fret count, we tried to infer the pitch offset, but 3 semitones is
> ambiguous.
>
> Instead, if we start with the pitch offset, we can have either 2 tones minus
> 1 semitone or 1 tone plus 1 semitone.  Then we can convert either one into a
> capo fret without any ambiguity at all.
>
> HTH,
>
>
It does indeed!

I'll probably try and put that in the capo-indicator engraver, but I'm
still trying to get my head around scheme and scheme engravers. I've
grabbed all the examples I can find of scheme engravers but I'm having
difficulty getting to grips with them and they're not much help (they
all seem so inconsistent).

When I get some time to sit down I'll have to send some emails to list
getting you and others to help me learn scheme properly ...

Cheers,
Wol

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