將洛奇的MML樂譜轉為beep（蜂鳴器）樂譜
阿新 • • 發佈：2018-12-22
最近對蜂鳴器音樂感興趣，但是找不到樂譜，於是想把其他樂譜轉為蜂鳴器樂譜。直接用MIDI轉換很困難，因為MIDI一個音軌可以同時發出不同的音，所以我想到了用以前玩過的遊戲中的樂譜（MML樂譜參考）
轉換器製作
音高頻率表
首先要知道每個音高對應的頻率，按照十二平均律算，標準音高A4是440Hz，一個半音相差21/12倍，一個八度相差2倍
FREQ_TABLE = [[0 for scale in range(12)] for octave in range(9)]
def gen_freq_table():
global FREQ_TABLE
# A4標準音高
FREQ_TABLE[ 生成表後直接硬編碼即可
# 音程 -> 音階 -> 頻率，按十二平均律算
FREQ_TABLE = [
[16, 17, 18, 19, 21, 22, 23, 24, 26, 28, 29, 31], # C0~B0（未使用）
[33, 35, 37, 39, 41, 44, 46, 49, 52, 55, 58, 62], # C1~B1
[65, 69, 73, 78, 82, 87, 92, 98, 104, 110, 117, 123],
[131, 139, 147, 156, 165, 175, 185, 196, 208, 220, 233, 247],
[262, 277, 294, 311, 330, 349, 370, 392, 415, 440, 466, 494], # C4~B4
[523, 554, 587, 622, 659, 698, 740, 784, 831, 880, 932, 988],
[1047, 1109, 1175, 1245, 1319, 1397, 1480, 1568, 1661, 1760, 1865, 1976],
[2093, 2217, 2349, 2489, 2637, 2794, 2960, 3136, 3322, 3520, 3729, 3951],
[4186, 4435, 4699, 4978, 5274, 5588, 5920, 6272, 6645, 7040, 7459, 7902]
]
詞法分析、語法分析
因為巨集語言比較簡單，這兩部分就和在一起寫了。輸入MML字串，輸出音符、預設音長等token
# Token等定義略
class SyntaxAnalyzer:
"""語法分析器（兼詞法分析器）"""
# 字元 -> 音階索引
SCALE = {
'C': 0, 'D': 2, 'E': 4, 'F': 5, 'G': 7, 'A': 9, 'B': 11
}
def __init__(self):
self._mml = ''
self._index = 0
self._line = 1
self._col = 1
self._res = [[]]
def _preprocess(self):
self._mml = self._mml.upper()
self._index = 0
self._line = 1
self._col = 1
if self._mml.startswith('[email protected]'):
self._index += 4
self._col += 4
self._res = [[]]
def parse(self, mml: str) -> List[List[Token]]:
"""返回音軌陣列，每個音軌包含多個Token"""
self._mml = mml
self._preprocess()
while self._index < len(self._mml):
line = self._line
col = self._col
if self._cur_char == ',':
# 新音軌
self._read_char()
self._res.append([])
elif self._cur_char == ';':
# 結束
self._read_char()
break
elif self._cur_char in 'CDEFGAB':
# 音符
self._output(self._read_note())
elif self._cur_char == 'R':
# 休止符
self._read_char()
self._output(Pause(line, col, self._read_length()))
elif self._cur_char == '&':
# 連線
self._read_char()
self._output(Joiner(line, col))
elif self._cur_char == 'L':
# 預設音長
self._read_char()
self._output(DefaultLength(line, col, self._read_length()))
elif self._cur_char == 'T':
# 播放速度
self._read_char()
tempo = self._read_number()
if tempo is not None and not 32 <= tempo <= 255:
raise MmlError(line, col, f'tempo = {tempo}，速度超出範圍')
self._output(Tempo(line, col, tempo))
elif self._cur_char == 'V':
# 音量
self._read_char()
volume = self._read_number()
if volume is not None and not 0 <= volume <= 15:
raise MmlError(line, col, f'volume = {volume}，音量超出範圍')
self._output(Volume(line, col, volume))
elif self._cur_char == 'O':
# 音程
self._read_char()
octave = self._read_number()
if octave is not None and not 1 <= octave <= 8:
raise MmlError(line, col, f'octave = {octave}，音程超出範圍')
self._output(Octave(line, col, octave))
elif self._cur_char in '><':
# 改變音程
self._output(ChangeOctave(line, col, 1 if self._cur_char == '>' else -1))
self._read_char()
elif self._cur_char == 'N':
# 絕對音高
self._read_char()
note_index = self._read_number()
if note_index is None or not 1 <= note_index <= 96:
raise MmlError(line, col, f'note_index = {note_index}，絕對音高超出範圍')
self._output(AbsoluteNote(line, col, note_index))
elif self._cur_char in ' \t\r':
# 空白
self._read_char()
elif self._cur_char == '\n':
# 新行
self._read_char()
self._line += 1
self._col = 1
else:
# 錯誤字元
raise MmlError(line, col, f'未預料到的字元"{self._cur_char}"')
return self._res
def _output(self, token):
self._res[-1].append(token)
def _read_char(self):
res = self._mml[self._index]
self._index += 1
self._col += 1
return res
@property
def _cur_char(self):
return self._mml[self._index]
def _read_number(self):
"""讀數字，非數字則返回None"""
if self._index >= len(self._mml) or not '0' <= self._cur_char <= '9':
return None
res = 0
while self._index < len(self._mml) and '0' <= self._cur_char <= '9':
res = res * 10 + int(self._cur_char)
self._read_char()
return res
def _read_length(self):
length = self._read_number()
has_dot = False
if self._index < len(self._mml) and self._cur_char == '.':
has_dot = True
self._read_char()
return Length(length, has_dot)
def _read_note(self):
line = self._line
col = self._col
scale = self.SCALE[self._cur_char]
self._read_char()
if self._index < len(self._mml):
if self._cur_char in '+#':
scale += 1
self._read_char()
elif self._cur_char == '-':
scale -= 1
self._read_char()
return Note(line, col, scale, self._read_length())
token轉換為beep譜
這裡要考慮tempo是所有音軌共用的，後面的音軌優先，所以每次選事件最小的音軌處理，如果時間相同則選擇後面的音軌
按照4分音符為一拍，持續時間計算方法：
class MmlParser:
class _Track:
def __init__(self, tokens):
self.tokens = tokens
self.index = 0
# 音程
self.octave = DEFAULT_OCTAVE
# 預設音長
self.default_length = DEFAULT_LENGTH
# 播放速度（BPM，一分鐘幾拍）
self.tempo = None
# 下一個音符開始時間
self.time = 0
# 前面有一個連線符，正在連線狀態
self.is_joining = False
self.beep_res = []
def output(self, frequency, duration):
self.time += duration
if not self.is_joining:
self.beep_res.append([frequency, duration])
return
if not self.beep_res:
raise MmlError(self.tokens[self.index].line, self.tokens[self.index].col, '缺少被連線的音符')
if self.beep_res[-1][0] == frequency:
self.beep_res[-1][1] += duration
else:
self.beep_res.append([frequency, duration])
self.is_joining = False
def __init__(self):
self._tracks = []
def parse(self, mml: str) -> List[List[List[int]]]:
"""轉換MML樂譜到beep譜
返回音軌陣列，每個音軌包含多個音符，每個音符為[頻率(Hz), 持續時間(ms)]，頻率為0代表延時
"""
self._tracks = [self._Track(tokens) for tokens in SyntaxAnalyzer().parse(mml)]
track = self._get_next_track_to_process()
while track is not None:
token = track.tokens[track.index]
if isinstance(token, Note):
# 音符
octave = track.octave
scale = token.scale
if scale < 0:
scale = 11
octave -= 1
elif scale >= 12:
scale = 0
octave += 1
if not 1 <= octave <= 8:
raise MmlError(token.line, token.col, f'octave = {octave}，音程超出範圍')
track.output(FREQ_TABLE[octave][scale], self._get_duration(track, token.length))
elif isinstance(token, Pause):
# 休止符
track.output(0, self._get_duration(track, token.length))
elif isinstance(token, Joiner):
# 連線
track.is_joining = True