Generate a wave file from a MIDI file with Pydub

Generate WAV from MIDI.md

Simple example of rendering a midi file with Pydub

Basically, this takes a MIDI input file (I just googled and grabbed one of Maroon 5's "Animal" – I know, I know) and generates a WAV file.

NOTE: This is the slowest midi rendering program I have ever seen!

Dependencies:

• Pydub (pydub.com)
  • pip install pydub
• mido (http://mido.readthedocs.org/en/latest/)
  • pip install mido

In this example I an rendering a MIDI file of Maroon 5's "Animals" from http://www.free-midi.org

ok, ok, ok - Here's the output:

Here is the output my program generated (converted to mp3):

output.mp3

Obvious issues:

• Tempo is hard-coded
• All instruments are rendered using a Sine wave, including drums. Would be better to use different signal generators depending which instrument is being rendered (Sine is fine for flute, square is closer to saxaphone, etc)
• This is REALLLY SLOWWW. I haven't looked at performance at all, but it took almost an hour (2014, 2.8 GHz i7, Macbook Pro) to render the wav file with the code above. LOL

One way to improve performance is to use a Mixer class like this one instead of just overlaying every note onto a silent "output" audio segment.

midi_to_wav.py

from collections import defaultdict
from mido import MidiFile
from pydub import AudioSegment
from pydub.generators import Sine

def note_to_freq(note, concert_A=440.0):
  '''
  from wikipedia: http://en.wikipedia.org/wiki/MIDI_Tuning_Standard#Frequency_values
  '''
  return (2.0 ** ((note - 69) / 12.0)) * concert_A

mid = MidiFile("./maroon_5-animals.mid")
output = AudioSegment.silent(mid.length * 1000.0)

tempo = 100 # bpm

def ticks_to_ms(ticks):
  tick_ms = (60000.0 / tempo) / mid.ticks_per_beat
  return ticks * tick_ms
  

for track in mid.tracks:
  # position of rendering in ms
  current_pos = 0.0

  current_notes = defaultdict(dict)
  # current_notes = {
  #   channel: {
  #     note: (start_time, message)
  #   }
  # }
  
  for msg in track:
    current_pos += ticks_to_ms(msg.time)

    if msg.type == 'note_on':
      current_notes[msg.channel][msg.note] = (current_pos, msg)
    
    if msg.type == 'note_off':
      start_pos, start_msg = current_notes[msg.channel].pop(msg.note)
  
      duration = current_pos - start_pos
  
      signal_generator = Sine(note_to_freq(msg.note))
      rendered = signal_generator.to_audio_segment(duration=duration-50, volume=-20).fade_out(100).fade_in(30)

      output = output.overlay(rendered, start_pos)

output.export("animal.wav", format="wav")

I added on the top of the script:

from collections import defaultdict

and it worked. Thanks!

Thank you so much!

The piano notes in my midi are no more audible after the conversion. How to retain it...??

Me Too.
How to retain it?