如何用PHP转换音乐和弦？

Question

我想知道如何在PHP中创建一个函数，该函数用于转换一些音乐和弦。

我将尝试解释它是如何在音乐理论中工作的。希望我别忘了什么。如果有错误，请帮我改正。

1.简单和弦.

简单的和弦几乎和字母表一样简单，它是这样的：

C，C#，D，D#，E，F，F#，G，G#，A，A# B

因此，如果最初的chord是E，并且我们想要转置+1，则得到的和弦是F。如果我们转置+4，得到的和弦是G#。

2.扩展和弦.

它们的工作方式几乎像简单的和弦，但包含更多的字符，这些字符在转换时可以安全地忽略。例如：

C#7，Dsus7，Emi，Fsus4，F#mi，G.

同样，和简单的和弦一样，如果我们转换Dsus7 +3= Fsus7

3.非根低音.

当低音演奏的音调与和弦的根音不同时，就会出现问题。这是由一个斜杠后的和弦，也需要转置。示例：

C/G、Dmi/A、F#sus7 7/A#

与示例1和例2一样，所有内容都是相同的，但斜杠后面的部分也需要转换，因此：

C/G +5= F/C

F#sus7/A# +1= Gsus7/B

因此，基本上，假设您有一个名为chord的PHP变量和转置值transpose。什么代码会把和弦转过来？

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';

我在StackOverflow，在这里上发现了一个存在的问题。他们谈论和弦推进的算法。

如何将音乐和弦与PHP进行转换，增加或减少半音？

Answer 1

快速解决办法：

<?php

// produces the expected result
echo transpose("F#sus7/C#",3);

function transpose($chord,$transpose)
{
    // the chords
    $chords = array("C", "C#", "D", "D#", "E", "F", "F#", "G", "G#", "A", "A#", "B");

    $result = "";

    // get root tone
    $root_arr = explode("/",$chord);
    $root = strtoupper($root_arr[0]);

    // the chord is the first character and a # if there is one
    $root = $root[0].((strpos($root, "#") !== false)?"#":"");

    // get any extra info
    $root_extra_info = str_replace("#","",substr($root_arr[0],1)); // assuming that extra info does not have any #

    // find the index on chords array
    $root_index = array_search($root,$chords);
    // transpose the values and modulo by 12 so we always point to existing indexes in our array
    $root_transpose_index = floor(($root_index + $transpose) % 12);

    if ($root_transpose_index < 0)
    {
        $root_transpose_index += 12;
    }

    $result.= $chords[$root_transpose_index].$root_extra_info;

    if(count($root_arr)>1)
    {
        // get the non root tone
        $non_root = $root_arr[1];
        // the chord is the first character and a # if there is one
        $non_root = strtoupper($non_root[0]).((strpos($non_root, "#") !== false)?"#":"");
        // get any extra info
        $non_root_extra_info = str_replace("#","",substr($root_arr[1],1)); // assuming that extra info does not have any #

        // find the index on chords array
        $non_root_index = array_search($non_root,$chords);
        // transpose the values and modulo by 12 so we always point to existing indexes in our array
        $non_root_transpose_index = floor(($non_root_index + $transpose) % 12);

        if ($non_root_transpose_index < 0)
        {
            $non_root_transpose_index += 12;
        }

        $result.= "/".$chords[$non_root_transpose_index].$non_root_extra_info;
    }

    return $result;
}

https://3v4l.org/Cd9Pg

在代码方面有很大的改进空间，我只是试着对它进行编码，使其易于理解。

Answer 2

在这里，我使用preg_replace_callback的正则表达式(使用匿名函数需要PHP5.3)。

function transpose($str, $t=0)
{
  // the chords
  $chords = ["C","C#","D","D#","E","F","F#","G","G#","A","A#","B"];

  // set transpose, return if none
  $t = (int)$t % 12 + 12; if($t % 12 == 0) return $str;

  // regex with callback
  return preg_replace_callback('~[A-G]#?~', function($m) use (&$chords, &$t) {
    return $chords[(array_search($m[0], $chords) + $t) % 12];
  }, $str);
}

eval.in演示 (用于测试请参阅regex101)

echo transpose("Cmi, C#7, Dsus7, Emi, Fsus4, F#mi, G C/G, Dmi/A, F#sus7/A#", -3);

阿米，A#7，Bsus7，C#mi，Dsus4，D#mi，E/E，Bmi/F#，D#sus7/G

Answer 3

好吧，有几件事你想处理。

首先，您希望能够在数组中循环。这很简单:使用模数操作符，它在php中是%。

function transpose($chord, $increment) {
  $map = array('A', 'A#', 'B', 'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#');

  // Get the index of the given chord
  $index = array_search($chord, $map);
  if($index === false)
    return false;

  // Get the transposed index and chord
  $transpose_index = ($index + $increment) % count($map);
  if($transpose_index < 0)
    $transpose_index += count($map);
  return $map[$transpose_index];
}

第二，你想要剔除对你重要的实际和弦。您可以使用正则表达式(RegEx)来完成这一任务。

function transposeFull($chords, $increment) {

  // This RegEx looks for one character (optionally followed by a sharp).
  //     .\#?
  // This RegEx looks for an optional series of characters which are not /
  //     [^\/]*
  // Put them together to get a RegEx that looks for an expanded chord
  //     (.\#?)([^\/]*)
  // Then, do it again, but add a / first, and make it optional.
  //     (\/(.\#?)([^\/]*))?
  $regex = '%(.\#?)([^\/]*)(\/(.\#?)([^\/]*))?%';

  // Note that the () allow us to pull out the matches.
  // $matches[0] is always the full thing.
  // $matches[i] is the ith match 
  //   (so $matches[3] is the whole optional second chord; which is not useful)
  $matches = array();
  preg_match($regex, $chords, $matches);

  // Then, we get any parts that were matched and transpose them.
  $chord1 = (count($matches) >= 2) ? transpose($matches[1], $increment) : false;
  $expanded1 = (count($matches) >= 2) ? $matches[2] : '';
  $chord2 = (count($matches) >= 5) ? transpose($matches[4], $increment) : false;
  $expanded2 = (count($matches) >= 6) ? $matches[5] : '';

  // Finally, put it back together.
  $chords = '';
  if($chord1 !== false)
    $chords .= $chord1.$expanded1;
  if($chord2 !== false)
    $chords .= '/'.$chord2.$expanded2;

  return $chords;
}