What's the difference between the t in 'stellar' vs the t in 'tell'? I seem to pronounce them identically, dictionary pronunciation guides (https://www.oxfordlearnersdictionaries.com/definition/englis... and https://www.oxfordlearnersdictionaries.com/definition/englis...) do not make a distinction..

[edit] ah, one (!) of the two "tell" audio recordings in that dictionary seems to pronounce it in a different way that would illustrate the aspiration, but that seems different to how I've usually heard 'tell' being pronounced.

Both recordings of the "tell" word exhibit aspiration. I guess it is perhaps more noticeable to me because I'm quite well-versed in phonetics.

A common way of illustrating aspiration is: hold a sheet of paper in front of your mouth (or your hand), as you say the words. "tell" will give you a noticeable puff of air as it leaves the mouth, as opposed to "stellar", which won't.

Maybe these recordings are helpful to you: https://en.wikipedia.org/wiki/Aspirated_consonant#Allophonic

Thanks, that was helpful, I seem to get the difference now - just the "tell" example wasn't working as I (apparently unlike most English speakers) seem to pronounce that word with an unaspirated t.

Are you a native English speaker? It's common for native speakers to be pretty deaf to the differences between allophones. Try recording yourself in Audacity saying "Tell the stellar tart to start stewing a tall stall too," then highlight the two "tell" sounds and listen to them repeatedly. Also the two "tart" sounds, the two "too"/"tew" sounds, and the two "tall" sounds. Maybe you'll be able to hear the puff of white noise that's missing in "stellar", "start", "stew", and "stall". That's the aspiration.

This is so hard to explain in text, given the variation of English accents and that aspiration is not meaningful in English. For my regional speech, the strongest difference would be something like the difference between the /k/ sounds in “kale” and “scale”. Nothing to do with my feelings for the vegetable, but it gets an extra scornful bit of turbulence.