Function istft 

pub fn istft(
    frames: &[Vec<Complex>],
    hop_size: usize,
    window_fn: &[f64],
) -> Vec<f64>

Compute the inverse STFT (overlap-add reconstruction).

Arguments

• frames – STFT frames from stft (each of length window_size).
• hop_size – hop size used when computing the STFT.
• window_fn – the same window used for analysis (for proper reconstruction).

Returns the reconstructed real signal.