Destructive and Non-destructive Editing

Broadly speaking there are two ways to edit audio. You can edit it such that your changes are easily reversible or you can edit it such that each edit is taken out on the file itself and difficult to reverse. The former is destructive and the latter is non-destructive.

Destructive Editing

Windows Sound recorder is the perfect example of a completely destructive editor. The only way to reverse changes is to undo them and, as soon as you save the file, all possibility of undoing is lost.

Furthermore, there is no over-sampling, no mixing at a greater bit-depth so all changes involving pitch and volume have a cumulatively negative effect on the file. Even if you were to double the volume and then, by means of the effect, rather than hitting undo, reduce the volume back to its previous level, owing to the maths involved, the file wouldn't be quite the same because of rounding errors.

If you were to turn a file up so loud that it clipped, reducing the volume again would simply make the distorted file quieter.

Semi-destructive Editors

This is not proper terminology, either an editor is destructive or it is not. The term is used here to demonstrate that some destructive editors can be kinder to audio than others. Sound Forge is a good example of such an editor.

Unlike Sound Recorder, Sound Forge has the option to allow users to undo even after a file has been saved because you can save project folders, in which every single state your work went through before completion is saved. Even so, the only way to reverse edit operations is to undo enough times to restore to the state you need to get back to. If you spot a mistake 50 operations later, undoing to the required point and then remembering exactly what you did and in what order, can be very tedious.

Sound Forge also has the advantage over sound recorder that, regardless of whether you use its project files or not, it mixes and applies effects at a higher bit-depth so the integrity of the file is preserved to a greater extent, i.e. the rounding errors that occur have far less of an effect.

Also, regardless of whether you use Sound Forge's project files, when you perform edits, temporary files are created for the undo states. This means that a file can be less destructively returned to an earlier state. If you take a file in Sound Forge, increase its volume so that it clips and then reduce it, the file will sound absolutely fine again. Without pressing undo, the data that was lost through clipping is restored by virtue of the use of temporary files, rather than all the changes being performed on the file itself.

Non-destructive Editors

The truly non-destructive editor greatly reduces one's dependence on the undo button as a way of fixing mistakes. No matter how many effects you apply, some or all of them can be removed at any time, however many operations were performed since their application. If you delete a piece of audio, all or part of that section can be reinstated at any time. Pieces of audio that overlap can be separated again.

this is all because of the way non destructive editors' project files work. Nothing is done to the original media at all. A set of instructions is simply written that tells the editor what parts of that media to play or render and what effects should be applied.

Say you increase the volume of a piece of audio by 6 DB, then decrease it by 3 DB, then decide that actually it sounds better increased from the original volume by 9 DB. When played and render, all previous instructions will be cancelled out by the last one, the instruction to increase the volume by 9 DB, which reduces cumulative rounding errors. In addition, non-destructive editors mix and process at higher bit-depths than the original files. Reaper mixes at 64-bit float by default, which is 4 times the bit-depth of CD-quality media.

Conclusion

The less destructive operations we can apply to audio before the final render the better. Non-destructive editors offer the greatest degree of flexibility and resilience to mistakes. They save a lot of time and frustration.