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Horrible. I actually tried applying image compression to sounds over a decade ago (was still in school, did that for Jugend forscht). I used a Fourier transfor

by ygra 10y ago

Horrible. I actually tried applying image compression to sounds over a decade ago (was still in school, did that for Jugend forscht). I used a Fourier transform to generate image sections of a specific window of samples and used that. In hindsight, perhaps just treating the waveform as image data may have been better. The idea behind what I did was to see whether a spectrogram can be compressed well, considering that there's lots of repetition and blank space usually. In any case, JPEG murders pretty much everything in thag representation.

retroencabulato 10y ago
It kind of reads like you have discredited frequency domain compression algorithms. FYI JPEG used a block-based DCT which is very similar to a Fourier transform.
- ygra 10y ago
  That was not my intent. I just noted that my approach came from visually inspecting spectrograms and noting that they might be compressed quite well by image compression algorithms. Only to notice in the end that lossy image compression completely butchers the signal with noise if doing that. Had I just used the original waveform as raw image data that wouldn't have been as much of a problem. Compression would still have changed the samples, but overall probably not as badly. Heck, I've been 17 when I did that. I certainly didn't really know much about the theory behind or why it almost certainly would fail. But I guess by now I wouldn't even attempt such craziness, so in a way it's probably a good thing to not know things too well, sometimes.
  - ska 10y ago
    The problem is that we are much more sensitive to audio distortion than visual, particularly dynamic (e.g.video). Pretty much all lossy audio compression does a bad job without a psycho-acoustic model, whereas image compression works pretty well on simple metrics. It doesn't help that psycho-visual modelling is less well understood (than audio).

by ygra 10y ago

retroencabulato 10y ago

It kind of reads like you have discredited frequency domain compression algorithms. FYI JPEG used a block-based DCT which is very similar to a Fourier transform.

ygra 10y ago
That was not my intent. I just noted that my approach came from visually inspecting spectrograms and noting that they might be compressed quite well by image compression algorithms. Only to notice in the end that lossy image compression completely butchers the signal with noise if doing that. Had I just used the original waveform as raw image data that wouldn't have been as much of a problem. Compression would still have changed the samples, but overall probably not as badly. Heck, I've been 17 when I did that. I certainly didn't really know much about the theory behind or why it almost certainly would fail. But I guess by now I wouldn't even attempt such craziness, so in a way it's probably a good thing to not know things too well, sometimes.
- ska 10y ago
  The problem is that we are much more sensitive to audio distortion than visual, particularly dynamic (e.g.video). Pretty much all lossy audio compression does a bad job without a psycho-acoustic model, whereas image compression works pretty well on simple metrics. It doesn't help that psycho-visual modelling is less well understood (than audio).