When deleting small sections of audio using Audacity (on both a Mac and a PC), I’ve sometimes noticed that the waveform to the left side of my edit changes. In other words, a change takes place in an area that I’m not editing. I need to be zoomed in fairly close to see the change in the waveform. It’s not clear to me what exactly is changing in the waveform because the change takes place very quickly. But the change seems to affect all of the audio that is visible to the left of where the cut was made.
If I click UNDO, the waveform for that section seems to revert to its previous form.
Note: This doesn’t happen every time. But, as I mentioned above, it happens on both Mac and PC.
Q: Have others also seen such unintended changes in the waveform and identified the problem? If so, what’s going on?
I presume that you are referring to a small change in the appearance of peaks and wiggles in the waveform rather than a major (omg it’s completely different ) change.
If so, then it’s nothing to worry about.
In order to reduce processing time, whenever possible, Audacity reuses the same graphical data to display the waveform, and to some degree can resize that data to fit the current view. However, in order to keep the graphical display looking like the actual audio, many operations will trigger redrawing the waveform. Because the graphics are rounded to the nearest pixel (Audacity does not yet have sub-pixel rendering), the redrawn waveform may often be very slightly different from the previous cached version.
In other words, the audio has not actually changed at all, it is just that the graphics have been redrawn and pixel values may be rounded slightly differently in the display at certain zoom levels.
It can happen when applying an effect to a selection too. I think it’s disconcerting but only a visual problem. I also don’t think it happens when zoomed in so far that you can see the samples, rather at intermediate zoom levels.