can i select a portion of audio and stretch it in order to extend the tone?
Sure. If the song ends with one single long note, zoom in, drag-select a portion of the last note, copy and paste it into the song’s end again and again. It will keep making that one long note longer and longer. Doesn’t have to be at the end, either. You can paste just before the end and the new note will fit in with the others.
Let us know if you get a tick or pop at the paste points.
I would be lazy and use Effect > Repeat… . It shows you the new length of the selection after the repeats.
If you’re wanting to stretch the last note of a recording, try the “Sliding Time Scale / Pitch Shift” effect: http://manual.audacityteam.org/o/man/effect_menu.html#slide
For most “real music” that is that I would suggest - a note at the end of a song tends to change over time, so pastes or repeats rarely sound right.
However I thought we might be talking about Generate > Tone, in which case there may be no need to use time stretching, which is always slightly lossy.
Clue in the title : paulstretch … Audacity Manual
You would need to create a mix of the original and the stretched version … Empty Void / Endless Abyss (Echo Effect) - #11 by Trebor
One of the proposed names for that effect was “Extreme Stretch”. That would have been appropriate.
i tried the looping, but it produced clicks, so i manually did some crossfading.
i tried paulstretch for another sample, and it worked quite well