audio.py

# Machine learning, flow and data
import tensorflow as tf
import numpy as np
import pandas as pd

# Audio
import pretty_midi

# Displaying
from IPython import display

# Get the absolute path of the directory and add it to sys.path in order to
# get the VAE class type
import sys
from pathlib import Path

directory = Path(__file__).resolve().parent
sys.path.insert(0, str(directory))

from model import VAE

# Extras
import collections


_CAP = 3501 # Cap for the number of notes
_SAMPLING_RATE = 16000 # Parameter to pass continuous signal to a discrete one
_INSTRUMENT_NAME = "Acoustic Grand Piano" # MIDI instrument used
_SCALING_FACTORS = pd.Series(
    {"pitch": 64.024558, "step": 0.101410, "duration": 0.199386}
) # Factors used to normalize song maps

def midi_to_notes(midi_file: str) -> pd.DataFrame:
  """
  Convert midi file to "song map" (dataframe where each note is broken
  into its components).

  Parameters
  ----------
  
  midi_file : str
      Path to the midi file.

  Returns
  -------
  song_map : pd.Dataframe
      3xN matrix where each column is a note, composed of pitch, duration and step.
  """
    
  pm = pretty_midi.PrettyMIDI(midi_file)
  instrument = pm.instruments[0]
  notes = collections.defaultdict(list)

  # Sort the notes by start time
  sorted_notes = sorted(instrument.notes, key=lambda note: note.start)
  prev_start = sorted_notes[0].start

  # Separate each individual note in pitch, step and duration
  for note in sorted_notes:
    start = note.start
    end = note.end
    notes['pitch'].append(note.pitch)
    notes['step'].append(start - prev_start)
    notes['duration'].append(end - start)
    prev_start = start


  # Put notes in a dataframe
  notes_df = pd.DataFrame({name: np.array(value) for name, value in notes.items()})
  notes_df = notes_df[:_CAP] # Cap the song to match the model's architecture
  song_map = notes_df / _SCALING_FACTORS # Scale
  return song_map


def display_audio(pm: pretty_midi.PrettyMIDI, seconds=-1) -> display.Audio:
  """
  Display a song in PrettyMIDI format as a display.Audio object.
  This method specially comes in useful in a jupyter notebook.

  Parameters
  ----------
  
  pm : str
      PrettyMidi object containing a song.
  seconds : int
      Time fraction of the song to be displayed.
      Default ``-1``, for which the full length is taken.

  Returns
  -------
  display_obj : display.Audio
      Song as an object allowing for display.
  """
    
  waveform = pm.fluidsynth(fs=_SAMPLING_RATE)
  # Take a sample of the generated waveform to mitigate kernel resets
  if seconds == -1: 
      waveform_short = waveform[:]
  else:
      waveform_short = waveform[:seconds*_SAMPLING_RATE]
  
  display_obj = display.Audio(waveform_short, rate=_SAMPLING_RATE)
    
  return display_obj
    

def map_to_wav(song_map: pd.DataFrame, out_file: str, velocity: int=50) -> pretty_midi.PrettyMIDI:
  """
  Convert "song map" to midi file (reverse process with respect to 
  midi_to_notes) and (optionally) save it, generating a PrettyMidi object in the process.

  Parameters
  ----------
  
  song_map : pd.DataFrame
      3xN matrix where each column is a note, composed of pitch, duration and step.
  out_file : str
      Path or file to write .mid file to. If None, no saving is done.
  velocity : int
      Note loudness, i. e. the hardness a piano key is struck with.
      Default ``50``.

  Returns
  -------
  
  pm : pretty_midi.PrettyMIDI
      PrettyMIDI object containing the song's representation.
  """

  # Get song map as dataframe
  contracted_map = tf.squeeze(song_map)
  song_map_T = contracted_map.numpy().T
  notes = pd.DataFrame(song_map_T, columns=["pitch", "step", "duration"]).mul(_SCALING_FACTORS, axis=1)
  notes["pitch"] = notes["pitch"].astype('int32').clip(1, 127)

  # Instantiate PrettyMIDI object and append notes
  pm = pretty_midi.PrettyMIDI()
  instrument = pretty_midi.Instrument(
      program=pretty_midi.instrument_name_to_program(
          _INSTRUMENT_NAME))

  prev_start = 0
  for i, note in notes.iterrows():
    # The VAE might generate notes with negative step and duration,
    # and we therefore need to make sure to skip these anomalies
    if (note['step'] < 0 or note['duration'] < 0):
        continue
      
    start = float(prev_start + note['step'])
    end = float(start + note['duration'])
    note = pretty_midi.Note(
        velocity=velocity,
        pitch=int(note['pitch']),
        start=start,
        end=end,
    )
    instrument.notes.append(note)
    prev_start = start

  pm.instruments.append(instrument)

  # If a path was specified, save as midi file
  if out_file:
      pm.write(out_file)
  return pm

def generate_and_display(model: VAE, 
                         out_file: str=None, 
                         z_sample: tf.Tensor=None, 
                         velocity: int=50, 
                         seconds: int=-1) -> display.Audio:
  """
  Generate a song, (optionally) save it and display it.

  Parameters
  ----------
  model : VAE
      Instance of VAE to generate the song with.
  out_file : str
      Path or file to write .mid file to.
      Default ``None``, for which no saving is done.
  z_sample : tf.Tensor 
      Song encoding used to generate a song.
      Default ``None``, for which an unconditioned piece is generated.
  velocity : int
      Note loudness, i. e. the hardness a piano key is struck with.
      Default ``50``.
  seconds : int
      Time fraction of the song to be displayed.
      Default ``-1``, for which the full length is taken.

  Returns
  -------
  display_obj : display.Audio
      Song as an object allowing for display.
  """
    
  song_map = model.generate(z_sample)
  wav = map_to_wav(song_map, out_file, velocity)
  display_obj = display_audio(wav, seconds)
                             
  return display_obj