Those are probably the most difficult.

If you have an instrument handy, try playing a diminished chord. What does it feel like to you? Do certain images or words come to mind? Do the same with an augmented chord and contrast the two.

To me, a diminished chord feels reaching, miserable, and dark. An augmented chord feels unresolved, demented, and nebulous.

I love 'Miserable' and 'Demented', @Al Barnard . Chord description at its finest!

yo man

They have different intervallic structures.

A diminished triad is a minor-third interval - or 3 semi-tones - twice; so, the root to the minor third is 3 semi-tones, and then the minor third to the diminished fifth is also 3 semi-tones.

An augmented triad, on the other hand, is a major-third interval - or 4 semi-tones - twice; so, the root to the major third is 4 semi-tones, and the major third to the sharp five is also 4 semi-tones.

Probably your ears are being tricked by the fact both triads have that same symmetry: 3-3 in the case of the diminished triad and 4-4 in the case of the augmented triad. It definitely takes time to hear the difference between the two.

I'd say that the diminished triad sounds a bit more evil! The augmented triad sounds a bit more suspenseful. These adjectives are only so helpful, though. Ultimately, comparing and contrasting them together is probably the best way to gradually hear the difference.

I have trouble telling the difference immediately as well. The character of the dissonance sounds similar to me. See if you can hear the root and then the 5th from there. Do you hear a note just above that fifth (augmented) or just below (diminished)?

Much appreciated, @Cuantas Vacas!

Augmented always sounds real spy and james bond to me haha

Been there my friend, takes practice, one day you suddenly click :) Hang in there!

diminished chords are 2 minor thirds stacked while augmented chords are 2 major thirds stacked on each other. singing the notes out helps a lot

I really struggle with this too, but I keep trying. With intervals, I'm like lvl 100 I don't know, but still lvl 8 with the dimish and augmented, major and minor.

The augmented chord reminds me of the tune Flowers on the Batman soundtrack by Danny Elfman

Whatever best works for you to determine the difference between augmented and diminished is exactly what you should do.
For me, I focus on the interval between two close notes and identify either a major or minor third .... but you should hear the diminished chord as closed in tightly, and the augmented as more open ... bigger intervals.

One more trick that might help you distinguish diminished and augmented triads is the following: the final note of an augmented triad, if you just sing it down a semitone, is a normal major triad. So when you're struggling, try singing that third note down a semi-tone and does it now sound like a major triad? If yes, it's an augmented triad.

Equally, if you think what you're hearing might be a diminished triad but you're not sure, try singing the final note up a semi-tone and then you should have the sound of a normal minor triad. (Note that this only works for diminished triads when they are in root position).

This happens to me too. I find helpful singing the tritone in the diminished chords. If it doesn´t fit is an augmented chord. Also, you could try to sing a major third from the root note of the chord, if it fits is augmented, if it doesnt then is diminished.

I always go with my gut or intuition when identifying chords. Diminished sounds like pure sadness to me while augmented sounds like craziness (or demented, as Al put it). For me the trickier distinctions are b5, 7(b5) and Aug7. Those three sound somewhat similar. So what I do is I go to the Chord listening test under exercises (right side section of the gym) and I click on personalize (top right corner) and choose only those three chords and play the chord listening test over and over until I can identify a sonic flavor for each of them. but it's tough!

Another way I use to differentiate Aug and Dim chords is to associate them with the whole tone scale and 1.5 tone scale. It has a very unique sound and if you play it regularly you'll get used to it.
Aug chords = whole tone scale. You can play ascending & descending Aug chords by moving it 1 step up and down. For Example Caug - Daug - Eaug - F#aug - G#aug- A#aug back to Caug.
Dim chords = 1.5 tone scale. You can play it ascending ^ descending by moving it 1.5 steps up and down. For example Bdim - Ddim - Fdim - G#dim back to Bdim.
:) Try it out!

That's a good one, @Seighart Bui ! Thank you!

Augmented sounds more spy

Yes. Aug is spy/mystery. Dim is more Terror/Reveal.
Also, what @Seighart Bui said. Play the scale.

I like to associate songs with each one. for example, a diminished chord can fit in my future by Billie Eilish, but augmented chords simply sound chaotic in my ears.

Augmented chords always sounded like a train somehow. (???)

Augmented chords sound as if something felt and is breaking, and the shattered pieces are on the floor. The diminished chords are like twisting something while pulling it apart. ☺ Hope it helps