ファミコン実機っぽいかえるのうた

!pip install mido numpy soundfile

import mido
import numpy as np
import soundfile as sf
from IPython.display import Audio, display

#---------------------------------------------
# パラメータ設定 / Parameters
#---------------------------------------------
sample_rate = 44100
amplitude = 0.35
duty_cycle = 0.25   # 矩形波デューティ比（ファミコンらしさ）
decay_time = 0.15   # 音の減衰時間（短く）
tempo_bpm = 100
ticks_per_beat = 480

#---------------------------------------------
# ① メロディ＋休符 / Melody with spacing
#---------------------------------------------
# 「かえるのうたが〜」＋ 0.5拍の間を追加
notes = [
    "C4","D4","E4","F4","E4","D4","C4",
    None,  # 間（休符）
    "E4","F4","G4","A4","G4","F4","E4","C4"
]
note_length = 480  # 1拍
rest_length = 240  # 0.5拍
note_map = {"C4":60,"D4":62,"E4":64,"F4":65,"G4":67,"A4":69,"B4":71,"C5":72}

#---------------------------------------------
# ② MIDIシーケンス生成 / Build simple sequence
#---------------------------------------------
mid = mido.MidiFile(ticks_per_beat=ticks_per_beat)
track = mido.MidiTrack()
mid.tracks.append(track)

tempo = mido.bpm2tempo(tempo_bpm)
track.append(mido.MetaMessage('set_tempo', tempo=tempo))

for n in notes:
    if n is None:
        # 休符
        track.append(mido.Message('note_off', note=60, velocity=0, time=rest_length))
    else:
        pitch = note_map[n]
        track.append(mido.Message('note_on', note=pitch, velocity=90, time=0))
        track.append(mido.Message('note_off', note=pitch, velocity=90, time=note_length))

#---------------------------------------------
# ③ MIDIを矩形波音声に変換 / Convert MIDI to 8bit square-wave audio
#---------------------------------------------
current_time = 0
active_notes = {}
events = []

for msg in mid.play():
    current_time += msg.time
    if msg.type == 'note_on' and msg.velocity > 0:
        active_notes[msg.note] = current_time
    elif msg.type in ['note_off', 'note_on'] and msg.note in active_notes:
        start = active_notes.pop(msg.note)
        duration = current_time - start
        events.append((msg.note, start, duration))

duration_total = max(s + d for _, s, d in events)
t = np.linspace(0, duration_total, int(sample_rate * duration_total), endpoint=False)
wave = np.zeros_like(t)

for pitch, start, dur in events:
    f = 440 * (2 ** ((pitch - 69) / 12))
    start_idx = int(start * sample_rate)
    end_idx = int((start + dur) * sample_rate)
    n = end_idx - start_idx
    phase = np.arange(n) * f / sample_rate
    sq = np.where((phase % 1) < duty_cycle, 1.0, -1.0)
    env = np.exp(-np.linspace(0, decay_time, n) * 5)
    tone = amplitude * sq * env
    wave[start_idx:end_idx] += tone

wave /= np.max(np.abs(wave))
sf.write("kaeru_famicom_spaced.wav", wave, sample_rate)

#---------------------------------------------
# ④ Colabで再生 / Play inside Colab
#---------------------------------------------
print("✅ ファミコン風『かえるのうた』（間あり・ピコピコ版）")
display(Audio("kaeru_famicom_spaced.wav", rate=sample_rate))

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🎧 改良ポイント

要素	内容
休符追加	音と音の間に0.5拍（120ms程度）の「間」を挿入
減衰短縮	チップチューン特有のパッと消える音を再現
音量少し上げ	実機ファミコンのクリッピング気味サウンドに近づけた
矩形波25%	NES矩形波チャンネル1・2の代表的デューティ比

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実行すると、
「ポッ・ポッ・ポッ」と間のある、より本物のファミコン感ある“かえるのうた”がColabで再生されます。