Actually, I've already asked this question in ardour's chat, but maybe somebody have additional information. The question is about "correction" of guitar (or something else) records. I know, this is "not true way" but sometimes it is very useful. For example: if I had to record drums, first of all I need to wrote "raw" guitar with metronome to help drummer to play better(without this raw guitar part, if we have only metronome, drummer sounds lifeless). So, we need VERY SMOOTH guitar part, to help play drummer play smooth. It will be very helpful to make this raw guitar using time-stretching instrument, like "sample editor" in cubase or "elastic tool" in pro tools. I'm not insist to improve this tool in ardour, but maybe sombody knows lv2 plugin or another program, which helps to align instrument line to metronome?