如何使用JavaScript转置音乐和弦？ [英] How do I transpose music chords using JavaScript?

问题描述

我想知道如何创建一个用于移调音乐和弦的javascript函数。

I was wondering how would one create a javascript function for transposing music chords.

由于我不希望每个人都成为这里的音乐家，我会尝试解释它在音乐理论中的作用。我希望我不要忘记一些事情。如果是的话，音乐家请更正我。

Since I don't expect everyone to be a musician here, I'll try to explain how it works in music theory. I hope I don't forget something. If yes, musicians, please, correct me.

1）简单的和弦

简单的和弦几乎是就像字母一样简单，它是这样的：

The simple chords are almost as simple as an alphabet and it goes like this:

C，C＃，D，D＃，E，F，F＃，G，G＃ ，A，A＃B

C, C#, D, D#, E, F, F#, G, G#, A, A# B

从B再次循环到C.因此，如果原始和弦是 E 我们想要转置+1，结果和弦是 F 。如果我们转置+4，结果和弦是 G＃。

From B it loops all over again to C. Therefore, If the original chord is E and we want to transpose +1, the resulting chord is F. If we transpose +4, the resulting chord is G#.

2）扩展和弦

它们几乎像简单的和弦一样工作，但包含更多的字符，在转置时可以安全地忽略它们。例如：

They work almost like the simple chords, but contain a few more characters, which can safely be ignored when transposing. For example:

Cmi，C＃7，Dsus7，Emi，Fsus4，F＃mi，G ...

Cmi, C#7, Dsus7, Emi, Fsus4, F#mi, G ...

再次，与简单的和弦一样，如果我们转置 Dsus7 + 3 = Fsus7

So again, as with the simple chords, if we transpose Dsus7 + 3 = Fsus7

3）非根低音音调

问题当低音演奏与和弦根音不同的音调时出现。这是以和弦后的斜线为标记，也需要调换。示例：

A problem arises when the bass plays a different tone than the chord root tone. This is marked by a slash after the chord and also needs to be transposed. Examples:

C / G，Dmi / A，F＃sus7 / A＃

C/G, Dmi/A, F#sus7/A#

与示例1和2一样，一切都是相同的，但斜杠后面的部分也需要转置，因此：

As with examples 1 and 2, everything is the same, but the part after the slash needs transpose too, therefore:

C / G + 5 = F / C

F＃sus7 / A＃ + 1 = Gsus7 / B

我认为这应该是全部，除非我忘记了什么。

I think this should be all, unless I forgot something.

所以基本上，假设你有一个名为 chord的javascript变量和转置值转置。什么代码会转换和弦？

So basically, imagine you have a javascript variable called chord and the transpose value transpose. What code would transpose the chord?

示例：

var chord = 'F#sus7/C#';
var transpose = 3; // remember this value also may be negative, like "-4"
... code here ...
var result; // expected result = 'Asus7/E';

推荐答案

有点像这样的东西：

function transposeChord(chord, amount) {
  var scale = ["C", "C#", "D", "D#", "E", "F", "F#", "G", "G#", "A", "A#", "B"];
  return chord.replace(/[CDEFGAB]#?/g,
                       function(match) {
                         var i = (scale.indexOf(match) + amount) % scale.length;
                         return scale[ i < 0 ? i + scale.length : i ];
                       });
}

alert(transposeChord("Dm7/G", 2)); // gives "Em7/A"
alert(transposeChord("Fmaj9#11", -23)); // gives "F#maj9#11"

注意我扔了F＃maj9＃ 11示例只是为了让您更多地考虑有关构成有效和弦名称的内容：您可能会发现一个不跟随字母的＃尖锐符号（在这种情况下它属于11） 。

Note that I threw in the "F#maj9#11" example just to give you more to think about with regard to what makes up a valid chord name: you may find a "#" sharp symbol that doesn't follow a letter (in this case it belongs to the "11").

显然，我的函数只能理解锐利，而不理解平面，并且不理解键，所以，例如， transposeChord（C / E，1）当它真的应该是C＃/ E＃时会给出C＃/ F。

And, obviously, my function only understands sharps, not flats, and doesn't understand keys, so, e.g., transposeChord("C/E", 1) will give "C#/F" when it really should be "C#/E#".

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