tapeAudioRestoration.py

#!./venv/bin/activate

"""
MPAI CAE-ARP Tape Audio Restoration.

Implements MPAI CAE-ARP Tape Audio Restoration Technical Specification.
It identifies and restore portions of the Preservation Audio File, providing:
- Restored Audio Files;
- Editing List
"""

import array
import numpy as np
import os
import shutil
import sys
import yaml
from argparse import ArgumentParser, RawTextHelpFormatter
from control import c2d, TransferFunction
from numpy import ndarray
from scipy.io import wavfile
from scipy.signal import tf2zpk, zpk2tf, lfilter
from mpai_cae_arp.io import Color, Style, prettify

__author__ = "Nadir Dalla Pozza"
__copyright__ = "Copyright 2022, Audio Innova S.r.l."
__credits__ = ["Niccolò Pretto", "Nadir Dalla Pozza", "Sergio Canazza"]
__license__ = "GPL v3.0"
__version__ = "1.0.1"
__maintainer__ = "Nadir Dalla Pozza"
__email__ = "nadir.dallapozza@unipd.it"
__status__ = "Production"


class CC:
    """
    Variables for customizing console colors
    """
    PURPLE = '\033[95m'
    CYAN = '\033[96m'
    DARK_CYAN = '\033[36m'
    BLUE = '\033[94m'
    GREEN = '\033[92m'
    YELLOW = '\033[93m'
    RED = '\033[91m'
    BOLD = '\033[1m'
    UNDERLINE = '\033[4m'
    END = '\033[0m'


def get_arguments() -> tuple[str, str, str, float, str, float]:
    """
    Method to obtain arguments from config.yaml file or command line.
    Default config.yaml, ignored if a command line argument is passed.
    :return: tuple consisting of nine variables:
             1) str specifying the working path;
             2) str specifying the name of the Preservation files, which is key element to retrieve necessary files;
             3) str specifying the equalization standard used when the tape was recorded;
             4) float specifying the speed used when the tape was recorded;
             5) str specifying the equalization standard used when the tape was read;
             6) float specifying the speed used when the tape was read.
    """

    if len(sys.argv) > 1:
        # Read from command line
        parser = ArgumentParser(
            prog="python3 tapeAudioRestoration.py",
            formatter_class=RawTextHelpFormatter,
            description="A tool that implements MPAI CAE-ARP Tape Audio Restoration Technical Specification.\n"
                        "By default, the configuration parameters are loaded from ./config.yaml file,\n"
                        "but, alternately, you can pass command line arguments to replace them."
        )
        parser.add_argument(
            "-w",
            "--working-path",
            help="Specify the Working Path, where all input files are stored",
            required=True
        )
        parser.add_argument(
            "-f",
            "--files-name",
            help="Specify the name of the Preservation files (without extension)",
            required=True
        )
        parser.add_argument(
            "-ew",
            "--equalization-w",
            help="Specify the name of the equalization standard used when the tape was recorded",
            required=True
        )
        parser.add_argument(
            "-sw",
            "--speed-w",
            help="Specify the speed used when the tape was recorded",
            required=True
        )
        parser.add_argument(
            "-er",
            "--equalization-r",
            help="Specify the name of the equalization standard used when the tape was read",
            required=True
        )
        parser.add_argument(
            "-sr",
            "--speed-r",
            help="Specify the speed used when the tape was read",
            required=True
        )
        args = parser.parse_args()
        working_path = args.working_path
        files_name = args.files_name
        standard_w = args.equalization_w
        speed_w = float(args.speed_w)
        standard_r = args.equalization_r
        speed_r = float(args.speed_r)
    else:
        # Read configuration file
        config = object
        try:
            config = yaml.safe_load(open('config/args.yaml', 'r'))
            if 'WORKING_PATH' not in config:
                print(prettify('WORKING_PATH key not found in config/args.yaml!', color=Color.RED))
                quit(os.EX_CONFIG)
            if 'FILES_NAME' not in config:
                print(CC.RED + 'FILES_NAME key not found in config.yaml!' + CC.END)
                quit(os.EX_CONFIG)
            if 'STANDARD_W' not in config:
                print(CC.RED + 'STANDARD_W key not found in config.yaml!' + CC.END)
                quit(os.EX_CONFIG)
            if 'SPEED_W' not in config:
                print(CC.RED + 'SPEED_W key not found in config.yaml!' + CC.END)
                quit(os.EX_CONFIG)
            if 'STANDARD_R' not in config:
                print(CC.RED + 'STANDARD_R key not found in config.yaml!' + CC.END)
                quit(os.EX_CONFIG)
            if 'SPEED_R' not in config:
                print(CC.RED + 'SPEED_R key not found in config.yaml!' + CC.END)
                quit(os.EX_CONFIG)
        except FileNotFoundError:
            print(CC.RED + 'config/args.yaml file not found!' + CC.END)
            quit(os.EX_NOINPUT)
        working_path = config['WORKING_PATH']
        files_name = config['FILES_NAME']
        standard_w = config['STANDARD_W']
        speed_w = config['SPEED_W']
        standard_r = config['STANDARD_R']
        speed_r = config['SPEED_R']
    return working_path, files_name, standard_w, speed_w, standard_r, speed_r


def check_input(working_path: str, files_name: str, standard_w: str, speed_w: float, standard_r: str, speed_r: float) -> tuple[str, str, str, str]:
    """
    Method to check that passed arguments are correct and that the environment is conformant to the standard;
    :param working_path: str representing the path where all files resulting from previous AIMs are stored,
    :param files_name: str representing the Preservation files name, to identify the input directory,
    :param standard_w: str specifying the equalization standard used when the tape was recorded,
    :param speed_w: float specifying the speed used when the tape was recorded,
    :param standard_r: str specifying the equalization standard used when the tape was read,
    :param speed_r: float specifying the speed used when the tape was read.
    :return: tuple consisting of three variables:
             1) str representing the path where the Preservation Audio File is stored;
             2) str representing the path where the files to be processed during the current execution are stored;
             3) the operating standard_w;
             4) the operating standard_r.
    """

    # Check for working path existence
    if not os.path.exists(working_path):
        print(CC.RED + 'The specified WORKING_PATH is non-existent!' + CC.END)
        quit(os.EX_CONFIG)
    # Check for Preservation Audio File existence
    audio_file = files_name + '.wav'
    paf_path = os.path.join(working_path, 'PreservationAudioFile', audio_file)
    if not os.path.exists(paf_path):
        print(CC.RED + 'Preservation Audio File not found!' + CC.END)
        quit(os.EX_NOINPUT)
    # Check for temp directory existence
    temp_path = os.path.join(working_path, 'temp')
    if not os.path.exists(temp_path):
        print(CC.RED + 'WORKING_PATH structure is not conformant!' + CC.END)
        quit(os.EX_NOINPUT)
    # Check for input directory existence
    temp_path = os.path.join(temp_path, files_name)
    if not os.path.exists(temp_path):
        print(CC.RED + 'The specified FILES_NAME has no corresponding files!' + CC.END)
        quit(os.EX_NOINPUT)

    # Configuration parameters check

    # Recording tape speed check
    if speed_w != 3.75 and speed_w != 7.5 and speed_w != 15 and speed_w != 30:
        print(
            CC.RED + 'Incorrect SPEED_W: \'' + str(speed_w) + '\'. Accepted value are: 3.75, 7.5, 15, 30.' + CC.END
        )
        quit(os.EX_CONFIG)

    # Reading tape speed check.
    if speed_r != 3.75 and speed_r != 7.5 and speed_r != 15 and speed_r != 30:
        print(
            CC.RED + 'Incorrect SPEED_R: \'' + str(speed_r) + '\'. Accepted value are: 3.75, 7.5, 15, 30.' + CC.END
        )
        quit(os.EX_CONFIG)

    # Equalization standard check.
    if not (standard_r == 'CCIR' or standard_r == 'NAB'):
        print(
            CC.RED + 'Incorrect STANDARD_R: \'' + standard_r + '\'. Accepted values are: CCIR, NAB.' + CC.END
        )
        quit(os.EX_CONFIG)
    if not (standard_w == 'CCIR' or standard_w == 'NAB'):
        print(
            CC.RED + 'Incorrect STANDARD_W: \'' + standard_w + '\'. Accepted values are: CCIR, NAB.' + CC.END
        )
        quit(os.EX_CONFIG)

    # CCIR speed check.
    if standard_w == 'CCIR' and speed_w == 3.75:
        print(
            CC.YELLOW + 'CCIR is undefined at 3.75 ips. Recording equalization standard is set to NAB.' + CC.END
        )
        standard_w = 'NAB'
    if standard_r == 'CCIR' and speed_r == 3.75:
        print(
            CC.YELLOW + 'CCIR is undefined at 3.75 ips. Reading equalization standard is set to NAB.' + CC.END
        )
        standard_r = 'NAB'
    # NAB speed check.
    if standard_w == 'NAB' and speed_w == 30:
        print(
            CC.YELLOW + 'NAB is undefined at 30 ips. Recording equalization standard is set to CCIR.' + CC.END
        )
        standard_w = 'CCIR'
    if standard_r == 'NAB' and speed_r == 30:
        print(
            CC.YELLOW + 'NAB is undefined at 30 ips. Reading equalization standard is set to CCIR.' + CC.END
        )
        standard_r = 'CCIR'

    return paf_path, temp_path, standard_w, standard_r


def get_correction_filter(standard_w: str, speed_w: float, standard_r: str, speed_r: float, fs: int) -> tuple[array, array, float, int]:
    """
    Method to establish correct filter transfer function coefficients;
    :param standard_w: str specifying the equalization standard used when the tape was recorded,
    :param speed_w: float specifying the speed used when the tape was recorded,
    :param standard_r: str specifying the equalization standard used when the tape was read,
    :param speed_r: float specifying the speed used when the tape was read,
    :param fs: float specifying the sampling frequency.
    :return: tuple consisting of four variables:
             1) array representing the filter numerator coefficients;
             2) array representing the filter denominator coefficients;
             3) float specifying the operating sampling frequency;
             4) int informing about the case number.
    """
    # CCIR time constants.
    t2_30 = 17.5 * 10 ** (-6)  # time constant CCIR_30
    t2_15 = 35 * 10 ** (-6)  # time constant CCIR_15
    t2_7 = 70 * 10 ** (-6)  # time constant CCIR_7.5

    # NAB time constants.
    t3 = 3180 * 10 ** (-6)
    t4_15 = 50 * 10 ** (-6)  # time constant NAB_15
    t4_7 = 50 * 10 ** (-6)  # time constant NAB_7.5
    t4_3 = 90 * 10 ** (-6)  # time constant NAB_3.75

    a = []
    b = []
    case = -1
    # This section will establish which time constants must be modified to obtain the desired equalisation standard.
    if standard_w == 'CCIR':
        if speed_w == 30:
            if standard_r == 'NAB':
                # Case 1
                if speed_r == 15:
                    fs = 2 * fs  # Doubling the sampling frequency
                    # Correction filter: NABw15_mod + CCIRr30
                    # - NAB constants divided by 2
                    t3 = t3 / 2
                    t4 = t4_15 / 2
                    # - CCIR_30 constant not altered
                    t2 = t2_30
                    # Filter coefficients
                    a = [t2 * t3, t2 + t3, 1]
                    b = [t3 * t4, t3, 0]
                    # Plot information
                    case = 1
                # Case 2
                elif speed_r == 7.5:
                    fs = 4 * fs  # Quadrupling the sampling frequency
                    # Correction filter: NABw7.5_mod + CCIRr30
                    # - NAB constants divided by 4
                    t3 = t3 / 4
                    t4 = t4_7 / 4
                    # - CCIR_30 constant not altered
                    t2 = t2_30
                    # Filter coefficients
                    a = [t2 * t3, t2 + t3, 1]
                    b = [t3 * t4, t3, 0]
                    # Plot information
                    case = 2
                # Case 3
                else:  # speed_r == 3.75
                    fs = 8 * fs  # Multiplying by 8 the sampling frequency
                    # Correction filter: NABw3.75_mod + CCIRr30
                    # - NAB constants divided by 8
                    t3 = t3 / 8
                    t4 = t4_3 / 8
                    # - CCIR_30 constant not altered
                    t2 = t2_30
                    # Filter coefficients
                    a = [t2 * t3, t2 + t3, 1]
                    b = [t3 * t4, t3, 0]
                    # Plot information
                    case = 3
            else:  # standard_r == 'CCIR'
                # Case 31
                if speed_r == 30:
                    print('Reference case: 31')
                    print(CC.GREEN + 'Nothing to do!' + CC.END)
                    quit(os.EX_OK)
                # Case 15
                elif speed_r == 15:
                    fs = 2 * fs  # Doubling sampling frequency
                    # Plot information
                    case = 15
                # Case 16
                else:  # speed_r == 7.5
                    fs = 4 * fs  # Quadrupling the sampling frequency
                    # Plot information
                    case = 16
        elif speed_w == 15:
            if standard_r == 'NAB':
                # Case 28
                if speed_r == 15:
                    # No speed change
                    # Correction filter: NABw15 + CCIRr15
                    # - NAB_15 constants not altered
                    t4 = t4_15
                    # - CCIR_30 constant not altered
                    t2 = t2_15
                    # Filter coefficients
                    a = [t2 * t3, t2 + t3, 1]
                    b = [t3 * t4, t3, 0]
                    # Plot information
                    case = 28
                # Case 6
                elif speed_r == 7.5:
                    fs = 2 * fs  # Doubling the sampling frequency
                    # Correction filter: NABw7.5_mod + CCIRr15
                    # - NAB constants divided by 2
                    t3 = t3 / 2
                    t4 = t4_7 / 2
                    # - CCIR_15 constant not altered
                    t2 = t2_15
                    # Filter coefficients
                    a = [t2 * t3, t2 + t3, 1]
                    b = [t3 * t4, t3, 0]
                    # Plot information
                    case = 6
                # Case 7
                else:  # speed_r == 3.75
                    fs = 4 * fs  # Quadrupling the sampling frequency
                    # Correction filter: NABw3.75_mod + CCIRr15
                    # - NAB constants divided by 4
                    t3 = t3 / 4
                    t4 = t4_3 / 4
                    # - CCIR_15 constant not altered
                    t2 = t2_15
                    # Filter coefficients
                    a = [t2 * t3, t2 + t3, 1]
                    b = [t3 * t4, t3, 0]
                    # Plot information
                    case = 7
            else:  # standard_r == 'CCIR'
                # Case 19
                if speed_r == 30:
                    fs = fs / 2  # Halving the sampling frequency
                    # Plot information
                    case = 19
                # Case 33
                elif speed_r == 15:
                    print('Reference case: 33')
                    print(CC.GREEN + 'Nothing to do!' + CC.END)
                    quit(os.EX_OK)
                # Case 20
                else:  # speed_r == 7.5
                    fs = 2 * fs  # Doubling the sampling frequency
                    # Plot information
                    case = 20
        else:  # speed_w == 7.5
            if standard_r == 'NAB':
                # Case 10
                if speed_r == 15:
                    fs = fs / 2  # Halving the sampling frequency
                    # Correction filter: NABw15_mod + CCIRr7.5
                    # - NAB constants multiplied by 2
                    t3 = t3 * 2
                    t4 = t4_15 * 2
                    # - CCIR_7.5 constant not altered
                    t2 = t2_7
                    # Filter coefficients
                    a = [t2 * t3, t2 + t3, 1]
                    b = [t3 * t4, t3, 0]
                    # Plot information
                    case = 10
                # Case 30
                elif speed_r == 7.5:
                    # No speed change
                    # Correction filter: NABw7.5 + CCIRr7.5
                    # - NAB_7.5 constant not altered
                    t4 = t4_7
                    # - CCIR_7.5 constant not altered
                    t2 = t2_7
                    # Filter coefficients
                    a = [t2 * t3, t2 + t3, 1]
                    b = [t3 * t4, t3, 0]
                    # Plot information
                    case = 30
                # Case 11
                else:  # speed_r == 3.75
                    fs = 2 * fs  # Doubling the sampling frequency
                    # Correction filter: NABw3.75_mod + CCIRr7.5
                    # - NAB constants divided by 2
                    t3 = t3 / 2
                    t4 = t4_3 / 2
                    # - CCIR_7.5 constant not altered
                    t2 = t2_7
                    # Filter coefficients
                    a = [t2 * t3, t2 + t3, 1]
                    b = [t3 * t4, t3, 0]
                    # Plot information
                    case = 11
            else:  # standard_r == 'CCIR'
                # Case 23
                if speed_r == 30:
                    fs = fs / 4  # Quartering the sampling frequency
                    # Plot information
                    case = 23
                # Case 24
                elif speed_r == 15:
                    fs = fs / 2  # Halving the sampling frequency
                    # Plot information
                    case = 24
                # Case 35
                else:  # speed_r == 7.5
                    print('Reference case: 35')
                    print(CC.GREEN + 'Nothing to do!' + CC.END)
                    quit(os.EX_OK)
    else:  # standard_w == 'NAB'
        if speed_w == 15:
            if standard_r == 'NAB':
                # Case 32
                if speed_r == 15:
                    print('Reference case: 32')
                    print(CC.GREEN + 'Nothing to do!' + CC.END)
                    quit(os.EX_OK)
                # Case 17
                elif speed_r == 7.5:
                    fs = 2 * fs  # Doubling the sampling frequency
                    # Correction filter: NABw7.5_mod + NABr15
                    # - NABw constants divided by 2
                    t3_mod = t3 / 2
                    t4_mod = t4_7 / 2
                    # - NABr constant not altered
                    t4 = t4_15
                    # Filter coefficients
                    a = [t3 * t3_mod * t4, t3 * (t3_mod + t4), t3]
                    b = [t3 * t3_mod * t4_mod, t3_mod * (t3 + t4_mod), t3_mod]
                    # Plot information
                    case = 17
                # Case 18
                else:  # speed_r == 3.75
                    fs = 4 * fs  # Quadrupling the sampling frequency
                    # Correction filter: NABw3.75_mod + NABr15
                    # - NAB constants divided by 4
                    t3_mod = t3 / 4
                    t4_mod = t4_3 / 4
                    # - NABr constant not altered
                    t4 = t4_15
                    # Filter coefficients
                    a = [t3 * t3_mod * t4, t3 * (t3_mod + t4), t3]
                    b = [t3 * t3_mod * t4_mod, t3_mod * (t3 + t4_mod), t3_mod]
                    # Plot information
                    case = 18
            else:  # standard_r == 'CCIR'
                # Case 4
                if speed_r == 30:
                    fs = fs / 2  # Halving the sampling frequency
                    # Correction filter: CCIRw30_mod + NABr15
                    # - CCIR_30 constant multiplied by 2
                    t2 = t2_30 * 2
                    # - NAB_15 constant not altered
                    t4 = t4_15
                    # Filter coefficients
                    a = [t3 * t4, t3, 0]
                    b = [t2 * t3, t2 + t3, 1]
                    # Plot information
                    case = 4
                # Case 27
                elif speed_r == 15:
                    # No speed change
                    # Correction filter: CCIRw15 + NABr15
                    # - CCIR_15 constant not altered
                    t2 = t2_15
                    # - NAB_15 constant not altered
                    t4 = t4_15
                    # Filter coefficients
                    a = [t3 * t4, t3, 0]
                    b = [t2 * t3, t2 + t3, 1]
                    # Plot information
                    case = 27
                # Case 5
                else:  # speed_r == 7.5
                    fs = fs * 2  # Doubling the sampling frequency
                    # Correction filter: CCIRw7.5_mod + NABr15
                    # - CCIR_7.5 constant divided by 2
                    t2 = t2_7 / 2
                    # - NAB_15 constant not altered
                    t4 = t4_15
                    # Filter coefficients
                    a = [t3 * t4, t3, 0]
                    b = [t2 * t3, t2 + t3, 1]
                    # Plot information
                    case = 5
        elif speed_w == 7.5:
            if standard_r == 'NAB':
                # Case 21
                if speed_r == 15:
                    fs = fs / 2  # Halving the sampling frequency
                    # Correction filter: NABw15_mod + NABr7.5
                    # - NABw constants multiplied by 2
                    t3_mod = t3 * 2
                    t4_mod = t4_15 * 2
                    # - NABr constant not altered
                    t4 = t4_7
                    # Filter coefficients
                    a = [t3 * t3_mod * t4, t3 * (t3_mod + t4), t3]
                    b = [t3 * t3_mod * t4_mod, t3_mod * (t3 + t4_mod), t3_mod]
                    # Plot information
                    case = 21
                # Case 34
                elif speed_r == 7.5:
                    print('Reference case: 34')
                    print(CC.GREEN + 'Nothing to do!' + CC.END)
                    quit(os.EX_OK)
                # Case 22
                else:  # speed_r == 3.75
                    fs = 2 * fs  # Doubling the sampling frequency
                    # Correction filter: NABw3.75_mod + NABr7.5
                    # - NABw constants divided by 2
                    t3_mod = t3 / 2
                    t4_mod = t4_3 / 2
                    # - NABr constant not altered
                    t4 = t4_7
                    # Filter coefficients
                    a = [t3 * t3_mod * t4, t3 * (t3_mod + t4), t3]
                    b = [t3 * t3_mod * t4_mod, t3_mod * (t3 + t4_mod), t3_mod]
                    # Plot information
                    case = 22
            else:  # standard_r == 'CCIR'
                # Case 8
                if speed_r == 30:
                    fs = fs / 4  # Quartering the sampling frequency
                    # Correction filter: CCIRw30_mod + NABr7.5
                    # - CCIR_30 constant multiplied by 4
                    t2 = t2_30 * 4
                    # - NAB_7.5 constant not altered
                    t4 = t4_7
                    # Filter coefficients
                    a = [t3 * t4, t3, 0]
                    b = [t2 * t3, t2 + t3, 1]
                    # Plot information
                    case = 8
                # Case 9
                elif speed_r == 15:
                    fs = fs / 2  # Halving the sampling frequency
                    # Correction filter: CCIRw15_mod + NABr7.5
                    # - CCIR_15 constant multiplied by 2
                    t2 = t2_15 * 2
                    # - NAB_7.5 constant not altered
                    t4 = t4_7
                    # Filter coefficients
                    a = [t3 * t4, t3, 0]
                    b = [t2 * t3, t2 + t3, 1]
                    # Plot information
                    case = 9
                # Case 29
                else:  # speed_r == 7.5
                    # No speed change
                    # Correction filter: CCIRw7.5 + NABr7.5
                    # - CCIR_7.5 constant not altered
                    t2 = t2_7
                    # - NAB_7.5 constant not altered
                    t4 = t4_7
                    # Filter coefficients
                    a = [t3 * t4, t3, 0]
                    b = [t2 * t3, t2 + t3, 1]
                    # Plot information
                    case = 29
        else:  # speed_w == 3.75
            if standard_r == 'NAB':
                # Case 25
                if speed_r == 15:
                    fs = fs / 4  # Quartering the sampling frequency
                    # Correction filter: NABw15_mod + NABr3.75
                    # - NAB constants multiplied by 4
                    t3_mod = t3 * 4
                    t4_mod = t4_15 * 4
                    # - NABr constant not altered
                    t4 = t4_3
                    # Filter coefficients
                    a = [t3 * t3_mod * t4, t3 * (t3_mod + t4), t3]
                    b = [t3 * t3_mod * t4_mod, t3_mod * (t3 + t4_mod), t3_mod]
                    # Plot information
                    case = 25
                # Case 26
                elif speed_r == 7.5:
                    fs = fs / 2  # Halving the sampling frequency
                    # Correction filter: NABw7.5_mod + NABr3.75
                    # - NAB constants multiplied by 2
                    t3_mod = t3 * 2
                    t4_mod = t4_7 * 2
                    # - NABr constant not altered
                    t4 = t4_3
                    # Filter coefficients
                    a = [t3 * t3_mod * t4, t3 * (t3_mod + t4), t3]
                    b = [t3 * t3_mod * t4_mod, t3_mod * (t3 + t4_mod), t3_mod]
                    # Plot information
                    case = 26
                # Case 36
                else:  # speed_r == 3.75
                    print('Reference case: 36')
                    print(CC.GREEN + 'Nothing to do!' + CC.END)
                    quit(os.EX_OK)
            else:  # standard_r == 'CCIR'
                # Case 12
                if speed_r == 30:
                    fs = fs / 8  # Dividing by 8 the sampling frequency
                    # Correction filter: CCIRw30_mod + NABr3.75
                    # - CCIR_30 constant multiplied by 8
                    t2 = t2_30 * 8
                    # - NAB_3.75 constant not altered
                    t4 = t4_3
                    # Filter coefficients
                    a = [t3 * t4, t3, 0]
                    b = [t2 * t3, t2 + t3, 1]
                    # Plot information
                    case = 12
                # Case 13
                elif speed_r == 15:
                    fs = fs / 4  # Quartering the sampling frequency
                    # Correction filter: CCIRw15_mod + NABr3.75
                    # - CCIR_15 constant multiplied by 4
                    t2 = t2_15 * 4
                    # - NAB_3.75 constant not altered
                    t4 = t4_3
                    # Filter coefficients
                    a = [t3 * t4, t3, 0]
                    b = [t2 * t3, t2 + t3, 1]
                    # Plot information
                    case = 13
                # Case 14
                else:  # speed_r == 7.5
                    fs = fs / 2  # Halving the sampling frequency
                    # Correction filter: CCIRw7.5_mod + NABr3.75
                    # - CCIR_7.5 constant multiplied by 2
                    t2 = t2_7 * 2
                    # - NAB_3.75 constant not altered
                    t4 = t4_3
                    # Filter coefficients
                    a = [t3 * t4, t3, 0]
                    b = [t2 * t3, t2 + t3, 1]
                    # Plot information
                    case = 14
    return a, b, fs, case


def correction(a: array, b: array, paf: ndarray, fs: int) -> ndarray:
    """
    Apply a correction filter to a Preservation Audio File;
    :param a: array of coefficients, specifying the numerator of filter transfer function,
    :param b: array of coefficients, specifying in the denominator of filter transfer function,
    :param paf: ndarray specifying the raw audio data of the Preservation Audio File,
    :param fs: int specifying the operational sampling frequency.
    :return: the corrected audio as a Restored Audio File.
    """

    # Analog transfer function
    h_a = TransferFunction(a, b)

    # Digital transfer function through bilinear digitisation
    h_d = c2d(h_a, 1 / fs, 'bilinear')
    num_d = h_d.num[0][0]  # Inspect Hd.num to see why [0][0] is needed...
    den_d = h_d.den[0][0]  # Same story here

    # Pole check

    # New pole frequency
    pole_frequency = 2
    # Move to zero-pole representation
    z, p, k = tf2zpk(a, b)
    # Check if the function presents a pole at 0 Hz
    for i in range(len(p)):
        if p[i] == 0:
            # Replace pole
            p[i] = -pole_frequency * 2 * np.pi
            print('\n' + CC.PURPLE + 'Pole at 0 Hz replaced!' + CC.END)
            # Back to transfer function representation
            ap, bp = zpk2tf(z, p, k)

            # Analog transfer function
            hp_a = TransferFunction(ap, bp)

            # Digital transfer function through bilinear digitisation
            hp_d = c2d(hp_a, 1 / fs, 'bilinear')
            num_d = hp_d.num[0][0]
            den_d = hp_d.den[0][0]

    print('\nFiltering Preservation Audio File...')
    # Filter Preservation Audio File
    raf = lfilter(num_d, den_d, paf, axis=0)
    # Again, wavfile.write() is stupid, and you must cast everything to not destroy your ears...
    raf = np.rint(raf).astype(paf.dtype)
    return raf


def save_file(file: ndarray, fs: int, temp_path: str, name: str):
    """
    Save an audio file to the given path with name 1.wav;
    :param file: ndarray specifying the raw audio data,
    :param fs: int specifying the operational sampling frequency,
    :param temp_path: str specifying the path where the file will be saved,
    :param name: str specifying the file name.
    :return: exit codes corresponding to the execution status.
    """
    raf_path = os.path.join(temp_path, 'RestoredAudioFiles')
    make_raf = False
    if not os.path.exists(raf_path):
        # Create directory
        os.mkdir(raf_path)
        make_raf = True
        print("Restored Audio Files directory '% s' created" % raf_path)
    else:
        print((CC.PURPLE + "Restored Audio Files directory '% s' already exists!" + CC.END) % raf_path)
        overwrite = input('Do you want to overwrite it? [y/n]: ')
        if overwrite.casefold() == 'y':
            # Overwrite directory
            shutil.rmtree(raf_path)
            os.mkdir(raf_path)
            make_raf = True
            print('Restored Audio Files directory overwritten')
        elif overwrite.casefold() != 'n':
            print(CC.RED + 'Unknown command, exiting' + CC.END)
            quit(os.EX_USAGE)
    if make_raf:
        print("Saving Restored Audio File to: '%s' ..." % raf_path)
        wavfile.write(os.path.join(raf_path, name + '.wav'), fs, file)


def main():
    """
    Main execution method.
    :return: exit codes corresponding to the execution status.
    """

    print(CC.BOLD + "\nWelcome to ARP Tape Audio Restoration!" + CC.END)
    print("You are using Python version: " + sys.version)

    # Get the input from config.yaml or command line
    working_path, files_name, standard_w, speed_w, standard_r, speed_r = get_arguments()
    # Check if input is correct
    paf_path, temp_path, standard_w, standard_r = check_input(working_path, files_name, standard_w, speed_w, standard_r, speed_r)

    # Display input parameters
    print('\nInput parameters:')
    print('    WORKING_PATH: ' + working_path)
    print('    FILES_NAME:   ' + files_name)
    print('    STANDARD_W:   ' + standard_w)
    print('    SPEED_W:      ' + str(speed_w) + ' ips')
    print('    STANDARD_R:   ' + standard_r)
    print('    SPEED_R:      ' + str(speed_r) + ' ips')

    # Preservation Audio File check
    print("Opening '%s'..." % paf_path)
    fs, paf = wavfile.read(paf_path)
    print('Preservation Audio File opened!')
    print('    FS:           ' + str(fs) + ' Hz\n')

    # Decision stage
    a, b, fs, case = get_correction_filter(standard_w, speed_w, standard_r, speed_r, fs)

    # Casting FS to int because wavfile.write() is stupid
    fs = round(fs)
    print('Reference case: ' + str(case))
    print('Operational FS: ' + str(fs) + ' Hz.')

    # Correction phase
    if len(a) != 0:
        # Not all cases present a correction filter!
        raf = correction(a, b, paf, fs)
        save_file(raf, fs, temp_path, '1')
    else:
        # Just save Restored Audio File, but with modified fs
        save_file(paf, fs, temp_path, '1')

    # End
    print(CC.GREEN + CC.BOLD + "Success!" + CC.END + '\n')


if __name__ == '__main__':
    main()