January 2011's Reaper workshop, by Mike Senior, looked at how best to hide audio edits. Mike has provided some audio examples of this in action.
Silence Edit Orig
Here's a section of lead vocal take before comping. You can hear that there is a little audio glitch in the middle of the word 'be'.
Silence Edit Fade
In this example the words 'be your' from the SilenceEditOrig have been replaced using material from a different take. In both cases the edits are rendered inaudible by virtue of their being located in small internal silences within the phrase itself: the first just before the letter 'b', and the second before the initial 'k' sound of the word 'queen'. A short 2ms crossfade was used for both edits.
Noise Edit Orig
Here's a section of lead vocal before comping. The 's' sound of the word 'slave' creates a short section of random waveform, which is ideal for hiding edits.
Noise Edit Fade
For this example I've replaced the last word of the NoiseEditOrig file ('slave') with an alternate version from another take. It was child's play to make the edit point inaudible, even with a tiny 2ms crossfade.
Premasked Edit Orig
Here's a section of mixed backing track that I've decided to alter using audio editing — I want the string line between 0:10 and 0:12 to repeat the note it played at the beginning of the file.
Premasked Edit Fade
In order to change the PremaskedEditOrig file's high string note at 0:10-0:12, I replaced it with a copied section from earlier in the same file. The edit points at the beginning and end of this replacement section were placed just before drum beats, and are therefore hidden from the listener's perception by psychological pre-masking effects. The crossfades were both just 2ms.
Matched Edit Raw
You can hear in this example file a section of a vocal comp in progress, with a mid-note edit between one take and the another. At the moment the edit has no crossfade at all, and the waveform mismatch across the boundary between the two regions, therefore, gives rise to a healthy click.
Matched Edit Aligned
Compared with the MatchedWaveformRaw file, all I've done here is slide the later take's waveform fractionally so that its repeating cycles match those of the earlier take. Already this dramatically reduces the click, even without any crossfade.
Matched Edit Fade
Adding a short equal-power crossfade (lasting just a couple of waveform cycles) to the edit in the MatchedEditAligned smooths the result even further. Although the edit is still not completely inaudible, in this case, while the vocal is soloed, it'll be more than good enough to pass muster when set against even the most basic backing arrangement.
Masked Edit Solo
Here's a lead vocal edit which sounds truly disgraceful — just listen to that click! Although you could spend time smoothing it out with a matched-waveform edit, there is an alternative method of concealment available: masking the edit.
Masked Edit Context
This file demonstrates how the horribly clunky vocal edit in MaskedEditSolo is completely inaudible within the context of a mix. I've not done any crossfading or anything, it's just that the edit has been chosen to coincide with a wacking great drum hit that masks it very effectively.