Message in MIDI

書接昨日，在 MIDI 裡面有固定的格式在記錄聲音的訊號，因為實在是太多了我們不會一一舉例，這邊只說明幾個常用到的，完整的官方文件請參照這裡

1.Program change
用於更改不同 channel 的樂器音色

    Message('program_change',channel,id,time =0)
    

• channel 為 0 ~ 15，更改這個值來更改聲音的通道，MIDI 默認有 16 個通道
• id 是樂器的編號，你可以在這裡查到，總共有 128 種

2. Note on
   音符的開始

   Message('note_on',note,vel,time,channel)
   

• note 值為 0~127，代表音高，比方說 60 就對應到 C4
• vel 值為 0~127，代表聲音的強度，默認是 64
• time 的意思是 "這個音符要在前一個音符結束後過多久開始"

3. Note off
   音符的結束，通常緊跟在 Note on 後面

    Message('note_off',note,vel,time,channel)
   

4. Control change (cc)
   控制聲音，比方說踩鋼琴的延音踏板這類的操作

    Message('control_change',channel,control,value,time)
   

• control 可以選擇要對聲音做哪些奇妙操作，詳細請參考這篇，這裡列幾個常用到的操作

  1. 64 - 延音踏版
  2. 71 - Harmonic Intens. 共鳴,可以控制聲音較突顯或隱誨
  3. 72 - Release Time 音符結束之後,聲音漸弱至完全沒有的時間
  4. 73 - Attack Time 音符開始之後,從無聲爬到至最高點的時間
  5. 74 - Brightness 調整聲音的明亮度

• value 則是控制實際操作的程度，比方說踩延音踏版這件事在 value =< 63 是 off 反之則是 on

開始編曲吧!

我們試著來編追追追 ~

from mido import Message, MidiFile, MidiTrack
mid = MidiFile()
track = MidiTrack()

 def play_part(track, note, len_ ,note_bias=0,vel=1.0,delay=0,change=False,double=False):
    # 每個節拍的時間長度
    temple = 60*60*10/75
    # 大調，參考別人的做法的，我也不是很懂樂理
    major_notes = [0,2,2,1,2,2,2,1]
    # C4 - 正中間的 DO
    base_note = 60
    bias = note_bias*12 + sum(major_notes[0:note])
    vel = round(64*vel)
    t_start = round(delay*temple)
    t_end =  round(temple*len_)
    if not double:
        track.append(Message("note_on",  note=base_note+bias,velocity=vel,time=t_start))
        track.append(Message("note_off", note=base_note+bias,velocity=vel,time=t_end))
    if change:
        track.append(Message("control_change",channel=0,control=64,value=64,time=t_start))
        track.append(Message("control_change",channel=0,control=64,value=0,time=t_end))
    if double:
        track.append(Message("program_change", channel=1,program=41 ,time = t_start))
        track.append(Message("note_on",channel=1, note=base_note+bias,velocity=vel,time = t_start))
        track.append(Message("note_off",channel=1, note=base_note+bias,velocity=vel,time = t_end))
        track.append(Message("program_change", channel=1,program=0 ,time=t_end))
    return track
    
    track = play_part(track,6,0.5)
    
######## 第一段 ###########

track = play_part(track,5,0.5)
track = play_part(track,6,0.5)
track = play_part(track,6,0.5)
track = play_part(track,5,0.5)
track = play_part(track,3,0.5)

track = play_part(track,2,0.5)
track = play_part(track,1,0.5)
track = play_part(track,2,0.5)
track = play_part(track,2,0.5)
track = play_part(track,1,0.5)
track = play_part(track,2,0.5)

track = play_part(track,2,0.5)
track = play_part(track,1,0.5)
track = play_part(track,2,0.5)
track = play_part(track,3,1.5)
track = play_part(track,5,0.5)
track = play_part(track,2,0.5)

track = play_part(track,3,1.0,change=True)

track = play_part(track,3,0.25,double=True)
track = play_part(track,5,0.25,double=True)
track = play_part(track,2,0.25,double=True)


######## 第二段 ###########

track = play_part(track,3,0.5)
track = play_part(track,6,0.5)
track = play_part(track,5,0.5)
track = play_part(track,2,0.5)
track = play_part(track,5,0.5)
track = play_part(track,2,0.5)

track = play_part(track,6,0.5,-1)
track = play_part(track,2,0.5)
track = play_part(track,1,0.5)
track = play_part(track,6,0.5,-1)
track = play_part(track,2,0.5)
track = play_part(track,2,0.5)

track = play_part(track,2,0.5)
track = play_part(track,5,1.5)
track = play_part(track,2,0.5)
track = play_part(track,2,0.5)
track = play_part(track,3,0.25)
track = play_part(track,5,0.25)


track = play_part(track,5,1.5)
track = play_part(track,5,0.5,-1)
track = play_part(track,5,0.5,-1)

track = play_part(track,6,0.5,-1)
track = play_part(track,6,1.0,-1,change=True)

track = play_part(track,5,0.5,-1,double=True)
track = play_part(track,6,0.5,-1,double=True)
track = play_part(track,6,1.5,-1,double=True)

######## 剩下的請加油 XD ###########

mid.tracks.append(track)
mid.save('new_song.mid')

小結

今天我們用 Python 實際編了一首曲子，其實體驗不是說很好，玩音樂的話果然還是要用一些專業的軟體比較好，但如果是要拿來做一些研究還是要從 python 出發，透過這次編曲也可以比較了解 MIDI 的運作>

參考資料

樂譜