Generally, the attack and release are pretty quick in Dr. Compressor. So you're mainly listening for the tails. The one that has longer tails on the snare and bass drum in particular is usually the more compressed.

Hi Kirk, i know Compression is hard to hear at first. Something that helped me was to listen for the surroundings/space around the instruments. If you compress and use make up gain, the reverb gets louder. Also compression makes the Drums sound closer "together". The sound color changes. You can hear it espacially with the snare carpet sounds. The Snare also gets more punch or boomyness sometimes. To hear the differences in higher levels, high quality head phones or monitor speakers are necessary.

Thanks, other than the Bluetooth from my phone, equipment shouldn't be the issue. I'm on Audeze Lcd2 and ibasso dx220. In the studio I've got Sennheiser HD650 and Apogee Rosettas. So it's definitely ME!
Let's say I'm presented with these two choices (using synth envelopes) :
Example A
1 - attack is at 10, sustain at 6, and decay is 1 sec
2 - Attack 5, sustain 4, decay 1 sec
2 is the right answer. Right?
Example B
1 - A 10, S 6, D 1
2 - A 10, S 8, D 1
Again, 2 right?
Now my problem is that I can't hear the difference between A.2 and B.2. Presented with those two choices, I would elect the latter, but I'd be wrong.
Graphs would make this easier to explain.

You're way overthinking it. Dr. Compressor is not about identifying specific compression parameters. That's what the Compressionist game is for. In Dr. Compressor you're just listening to how it sounds. It doesn't matter how it was made to sound that way. Which sample has the smallest dynamic range? That's what you're listening for.

Have checked out the game description?
==> "attack & release are very short for easier recognition"
In the game the difference isn't emphasized by the variation of Attack/Release settings but the amount of compression.
And compression isn't ADSR based, the best is to pop in a compressor in your DAW, set A/R as mentioned above. Then squash it hard to magnify the change and listen. Same thing happening in the game just in a gentle way.

I'm definitely over thinking it because I'm not sure on what to be focused! Is dynamic range relative or absolute?
Just gave Compressionist a shot, and it seems to be a better tool for how I like to learn. Thanks!

I had a hard time with hearing this too at first. I watched this video and then I went to my daw pulled up a drum loop then set a compression plug in to fast time fast release then turned it on and off to hear the difference. The main thing is the compression controls the transient of the drum kit so you hear the tail more clearly. Hope that helps.

For Dr. Compressor it's all relative. Dynamic range is about the difference between the loudest thing and the quietest thing. So you're trying to listen for which sample has the smallest difference between the loudest part and the quietest part. So you're not listening for overall loudness. One sample could be louder overall than the other but still have a smaller dynamic range.

Listen to the dynamic range of a specific drum/hat, remember difference between the quietest and the loudest sound, then compare to the second sample. They aren't adjusted to the same volume, which makes it even harder on advanced levels.

Oh nice headphones there. =) Do you prefer the audeze or the hd650 for mixing? And why?

@Marius Heinze The Sennies by a large margin. I can wear them all day if I have to, and they're much flatter than the LCD2, the latter of which is closed back. Now which one is more enjoyable from an audiophile's perspective? Hmmmm

This is a cool experiment that might help you.
https://mixcoach.com/train-ears-part-2-hearing-compression-compression-distortion/
Each compressor offers different tonal characteristics, so you might enjoy doing the experiment with different compressors and tracks.

First i focused on the difference between pumping effects due to compression vs more direct signal, which was good enough to get through the first levels. But then it gets tougher and i started to focus on the volume difference of each instrument. If more compressed, the instruments are closer loudness wise and so more compact. Most of the time you got it if you recognize the loudest instrument getting closer to the rest of the instruments.

Hi!
For me what always works is that I listen to how dynamic the louder hits are compared to the softer parts of the groove. The compressed example will have less of this difference and will feel flat compared to the unprocessed one.
This even works when the compressor doesn't affect the tail/bring up the room that audible.