Spectral Editing Review

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Peter 02Jun19: This page is a Work-In-Progress to review the current state of Spectral Selection and Spectral editing. I have recently been working on improving the documentation in the Manual for Spectral Selection and Editing and it has made me notice a few rough edges that I think we should be looking at smoothing off. In some cases there are existing bugs logged for some of these rough edges, Spectral editing is a very powerful tool in the right (expert) hands - and we should be working to make it the best it can be.

Spectral editing versus non-spectral editing - and Bug #917

The one thing that struck me when I started recent spectral testing to help me update the Manual is just why do we mix spectral and non spectral editing I would expect greater purity.

  • In Spectrogram view one can make a spectral selection and
    • Apply one of the three spectral effects to that spectral selection
    • Apply other effects to the selection - but the spectral part of that selection is ignored, the effect is applied to the entire spectral range of the temporal selection (invisibly to the user who may well be unaware of it - no warning is given and no indication in the GUI - rather a very close read of the Manual is required)
  • In Waveform view (even if you have a spectral selection hanging over from being in Spectrogram view)
    • if you try to apply any of the three spectral effects you will get an error message saying no-can-do (so greater purity here).
    • The error message could (and should) be improved - as it doesn't tell the user to switch to Spectrogram view
    • also the message tells the user to make a spectral selection - but the canny user who has turned on The Spectral Selection toolbar will observe that they do indeed have a spectral selection present (or they can make or change a spectral selection when in Waveform views using the Spectral Selection toolbar).

When I got my spectral naïve "mystery shopper" to test run the Manual pages and the app - the first thing she said when she switched into Spectrogram view, made a selection and went to the Effect menus was: "Why have I got all those other effects available, shouldn't they be grayed out - or not even present in a spectral effect menu"

Bug #917 relates to this "Enh: Spectral Selection only enabled for spectral edit effects.":

Paul notes in this bug thread that "We really want spectral cut, copy, and paste commands." available in Spectrogam view and to be applied spectrally

Recommendation

I think it would be much better if:

  1. Spectral editing effects (the three of them) are the only available effects in Spectrogram view, with either:
    • non-spectral effects grayed-out
    • a special Spectral effect menu with just the three spectral effects
  2. Waveform views editing shows as available only the non-spectral effects with either:
    • spectral effects grayed-out
    • the effect menu not having entries for the three spectral effects
    • but note that some of the "normal" effects may be applicable to a spectral selection - a good example is Echo
I suspect the graying out will be simpler - albeit less "pure", but still satisfactory.


No Spectral Selections in Waveform View

The title I have here is misleading. One can perfectly well have Spectral selections in Waveform views

  1. make spectral selection in Spectrogram view and switch to Waveform view
  2. label a spectral selection in Spectrogram view, do other stuff, switch to Waveform view and double click the label to select it (the label stores the frequencies)
  3. Enable the Spectral Selection toolbar while in Waveform view, make a temporal selection and then manipulate the numbers in the toolbar to create a spectral selection.

There are a couple of problems associated with this.

  1. The spectral selection is invisible to the user in Waveform view unless and until the user turns on the Spectral Selection toolbar (and thinks to observe it. There is no visual cue on the waveform itself (unlike when in Spectrogram view where the spectral selection is clearly visible - unless in white space, see below)
  2. If you are aware of the invisible spectral selection and try to run any of the three Spectral effects you will get an error message.

This relates to the previous issue - the lack of GUI design "purity".

Recommendation

Spectral selections should ideally not be available when in Waveform view or when switching from Spectrogram to Waveform view. Especially there is nothing you can do with spectral selection in Waveform view.


The Spectral Selection Toolbar

I note that labels store the definition of a spectral selection by saving the low frequency and the high frequency. However the Spectral Selection Toolbar has as it's default setting Center Frequency and Width - so the two usages are not consistent (and we do like consistency in Audacity)

Recommendations

Either:

  1. retain the two field Spectral Selection Toolbar but make Low Frequency / High Frequency the default setting
  2. extend the Spectral Selection Toolbar to be a four field bar: Low Frequency, High Frequency, Center Frequency, Width

The second option could be done in addition to the first - added as a third choice from the dropdown


Do we really need per-track settings for Spectral Selection?

Steve wrote elsewhere "I've never seen the point in ever disabling the "Spectrogram Settings" option in the track dropdown menu. Only a small issue, but it's just an unnecessary imposition on workflow."

I'm strongly reminded to agree with Steve here. The per-track ability to turn off (or on) Spectral Selection for just that track - and just while Audacity is active (the setting is not "remembered") - is an unnecessary and un-needed complication. Much better to have the global project (in fact cross-project) setting in Spectrograms preferences.

Recommendation

  • Remove the setting at the bottom of the Audio Track: Spectrogram settings
  • better still remove all those pre-track settings, and thus the dialog and menu entry, in favor of global settings in Preferences.


Bug #1098

P4 Bug #1098 - Enh: Frequency selection is not visible in white space

This is currently rated as a P4 bug -but to my mind it warrants higher, at least P3 (so we get a Release Note) and marginal P2.

It is very poor that when making a spectral selection which involves white space, only the temporal part of the selection is shown higlighted. Now while you can't do much with a spectral white space selection the user should at least get a decent visual cue on the spectrogram white space. Sure the user gas the S[pectral Edit Toolbar, if they've bothered to turn it on and if they've bothered to look at it - but they do deserve a better visual cue in the GUI.

Recommendation

Spectral selections in white space to show the "box" somehow.


Bug #2081

P3 Bug #2081 - Frequencies added to labels by "invisible" spectral selection

One has to ask the basic question: is the label the right place to store the spectral selection (if any) along with the temporal bounds - probably yes, but as this bug points out there are some rough edges that could (and probably should) be discussed and smoothed out.

Recommendation

More discussion needed


Tip in the Manual about "Nyquist frequency"

In one of the Tips on this page] it is written:

  • "When the upper boundary is at the Nyquist frequency of the track you can drag that boundary down by carefully hovering the mouse near the top of the track until the single up-arrow pointer appears then left clicking and dragging down."

Similarly in the Limitations section.

And in this section. And this section too.

There is no explanation on that page of what the "Nyquist frequency of the track" is and what it does  :=//

Recommendation

A little expansion of the text to provide clarity.