ifftSynth.py

'''
Synthesizes an audio page from a spectrum.  
'''
import numpy as np
from harmonicSynth import Harmonic

class IfftSynth:
    def __init__(self, SR, PAGE_LEN):
        self.SR = SR
        self.PAGE_LEN = PAGE_LEN
        self.SPECTRUM_SIZE = (PAGE_LEN // 2 + 1, )
        self.last_power = 0
        self.last_signal = None

    def _eat(self, harmonics, base_spectrum):
        if base_spectrum is None:
            spectrum = np.zeros(self.SPECTRUM_SIZE)
        else:
            spectrum = base_spectrum
        for freq, mag in harmonics:
            try:
                spectrum[round(
                    freq / self.SR * self.PAGE_LEN
                )] += mag
            except IndexError:
                continue
        signal = np.fft.irfft(spectrum) * self.PAGE_LEN * 2
        # For some reason you need a "* 2" 
        power = np.sum(np.abs(spectrum))
        # power = signal[0]
        if power == 0:
            if self.last_power == 0:
                return signal, power, signal
            else:
                mask = np.linspace(
                    1, 0, self.PAGE_LEN, 
                )
                return self.last_signal * mask, power, signal
        else:
            mask = np.linspace(
                self.last_power / power, 1, self.PAGE_LEN, 
            )
            return signal * mask, power, signal
    
    def eat(self, harmonics, base_spectrum = None):
        output, power, signal = self._eat(
            harmonics, base_spectrum, 
        )
        self.last_power = power
        self.last_signal = signal
        return output