Re: Spectral Editing is Not User Friendly

On 9 October 2017 at 00:34, Federico Miyara <[email protected]>
wrote:

>
> Steve and friends,
>
> I like the idea of being able to export the spectrogram, edit in an image
> editor, and then import back into Audacity. I presume that what you have in
> mind is similar to the software "Photosounder" (http://photosounder.com/).
> That would be a totally new feature, with only superficial similarity to
> the current "spectral edit" feature.
>
>
> I don't think it is theoretically possible to edit the spectrogram in an
> image processor (even if it were a customized one for Audacity) and get a
> valid spectrogram of the processed signal from which the processed signal
> could be recovered.
>


See this video: https://www.youtube.com/watch?time_continue=37&v=W8MCAXhEsy4

Editing any of those images in an image processor prior to 'converting'
them to sound does change the sound that is produced. Editing a spectrogram
in an image processor may not give intuitively predictable effects, but it
certainly would give an effect. For 'creative' use, the technical
limitations may be an asset.

Steve



>
> First of all, the spectrogram has no phase information, so colors alone
> cannot represent the correct sound, even the original one. In other words,
> the spectrogram drawing is not a reversible operation, even if no
> transformation or effect is applied.
>
> Second, the color map is a single-dimension one, defined by the linear
> interpolation of five colors which are just points on a bi-dimensional
> color map. Unless we could ensure the map color of the image processor is
> restricted to the colors contained in the piecewise linear path
> representing amplitudes, we would get meaningless spectrograms.
>
> Third, there is a limitation in resolution given by the size of the window
> so spectrograms do not present a continuous spatial transition of colors.
> Instead there are small but noticeable rectangles whose areas depend on the
> time-frequency uncertainty principle. If the FFT size is large, they are
> very short (high frequency resolution) and wide (low time resolution); if
> FFT size is small, they are very tall and narrow instead.
>
> A possibility would be to take advantage of the bi-dimensional nature of
> the full visible color map and represent the FFT complex numbers (retaining
> the phase information), which are also bi-dimensional, as colors. I guess
> several people have already tried some experiments on this (I mean the
> graphic representation; the concept of complex spectrogram is frequently
> used in signal processing). I also guess the spectrogram image would be
> stunning but far from being intuitive. Moreover, it would be very difficult
> to figure out the result of a given graphic effect, as well as what to do
> with the image to get the desired signal effect.
>
> The only practical approach is to simulate the spectrogram editing for
> very simple operations, such as zero or one gain (or real gain or
> attenuation).
>
> This is the approach we had presented (with Luciano). Our plugin allowed
> to draw closed regions of arbitrary shape to be either filtered out or
> retained . The plugin was based on overlapping time-varying FFT filter. Whatever
> the case, the retained part has gain 1 and the rejected part has gain 0. The
> idea could be extended to support drawing with an "attenuating pencil"
> which would apply a given gain (picked from a gray shade map).
>
> You mentioned Photosouder. I skimmed through the user guide and there is
> no hint as to what is actually doing when importing an image. What I'm
> pretty sure is that when editing an already loaded or computed spectrogram
> it does not re-synthesize the sound from the image, but processes the
> signal and recalculates the spectrogram.
>
> In other words, for an arbitrary image (say, a photo), it tries to
> represent it within the available color map and spectral and time
> resolution without concern for phase, but they have the advantage that we
> don't know a priori how the image "sounds"... And for a true spectrogram,
> it just simulates the image editing.
>
> Regards,
>
> Federico
>
>
>
> On 06/10/2017 11:19, Steve the Fiddle wrote:
>
> Hi Nikita,
>
> Spectral Editing in Audacity is a fairly new, and not yet fully developed,
> feature. Despite its shortcomings, it was considered to still be useful
> enough to include in the Audacity release.
>
> I like the idea of being able to export the spectrogram, edit in an image
> editor, and then import back into Audacity. I presume that what you have in
> mind is similar to the software "Photosounder" (http://photosounder.com/).
> That would be a totally new feature, with only superficial similarity to
> the current "spectral edit" feature.
>
> The current feature is really a 'simulation' of editing the spectrogram,
> rather than actually editing it. How it works is that the selected spectral
> region sets two frequency parameters (high and low). Specially crafted
> effects (the "Spectral" effects) can then use these parameters to control
> their behaviour. The effects then process the audio data as would any other
> audio effect. So the effect is not actually acting on the spectrogram - it
> acts on the audio, and the spectrogram is updated from the processed audio.
>
> Steve
>
> On 6 October 2017 at 13:38, Nikita Sadkov <[email protected]> wrote:
>
>> Hi! It was an amazing discovery, that Audacity now supports spectral
>> editing - arguably one of the most fundamental features, especially if
>> you want to synth custom sfx for your project or edit some badly
>> recorded material from https://freesound.org
>>
>> My complain is that it is very obscure and tedious to use in its
>> current form. You have to separately enable spectral selection and use
>> "Spectral edit ..." tools under "Effect" menu. I.e. you can't just
>> press Del to clear the frequencies or use Draw Tool (F3) to paint your
>> sfx with mouse.
>>
>> So I think it would make Audacity order of magnitude more useful, if
>> it copies UI from Sony SpectraLayers, together with layers, which
>> works just like a raster editor, but unfortunately lacks waveform
>> editing capabilities. Also, it would be nice feature to export
>> spectrum plot into png files, so people could edit it in GIMP and then
>> import back into Audacity.
>>
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>
>
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> > About
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When asking for help on this list, please include the following information, so we can
help you properly:

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* Exactly what three digit version number of Audacity you are using (Help > About
   Audacity, or Audacity >  About Audacity on a Mac computer)

* If this is a recording problem, what equipment you are recording with, and how is it
   connected to the computer?

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