Recreating the spectrogram face • Hacker News Board

Re: Recreating the spectrogram face

#21

Post by sneak » Sun, Oct 26, 2014, 6:51 PM UTC

FraKtus wrote: post #18

MetaSynth is all about that, you can import visuals, draw over them, filter them and then go back to audio, MetaSynth is available since a very long time, it was first running on Mac OS 9. http://www.uisoftware.com/MetaSynth/index.php

This is what RDJ used to make the sounds in the b-side on Windowlicker.

Re: Recreating the spectrogram face

#22

Post by sneak » Sun, Oct 26, 2014, 6:52 PM UTC

rikkus wrote: post #2

This made me listen to some Aphex Twin. Ouch. Luckily I soothed my ears with some Black Dog: https://www.youtube.com/watch?v=GUl6iJlEeTE

Don't be a jerk, please.

Re: Recreating the spectrogram face

#23

Post by AidanChurch » Tue, Oct 28, 2014, 5:20 AM UTC

sysk wrote: post #19

Forgive my ignorance but does a spectrogram carry all the information necessary to reproduce the sound that generated it? For example, assuming I had the spectrogram of a song, could I play the song using it?

The Discrete-Time Fourier Series is invertible. The problem is that for each pixel the Fourier series is a complex number and what is plotted is the magnitude (so the phase is not shown). Reconstructing a signal from only the magnitudes of the Fourier coefficients is ill-posed, i.e. there are multiple signals with the same Fourier coefficient magnitudes.

Still there is active research on reconstructing signals from only the Fourier magnitudes (under several assumptions). This is called the 'phase-retrieval problem'. http://en.wikipedia.org/wiki/Phase_retrieval