Interesting topic, Chris!

As a quick reply, here are a couple of past RO threads that include references to the human ear's response to transients:

1. One
2. Two

I think that the first thing we need to clarify is that Transients are not the same thing as "Peaking".
There's seems to have been a leaning towards describing these two terms as being one in the same in the last few years ( Im not exactly sure why)...
Certainly some Transients can cause Peaking to occur, and there are some instruments by their inherent nature that tend to have a lot of transients (drums vs flute, for example) but they are also an important part of what makes up the Dynamics of music.
Also, different mics, pres and gain reduction devices look at - and respond to - transients differently, even if the transients are exactly the same. FET compressors react differently to transients than Opto based compression does. Certain mics and preamps will often lend a very nice harmonic edge to transients. Analog tape reacted - and sounded - differently than digital converters do when they are fed certain transients. I think that a large part of the industry tends to look at transients as a "bad thing" which need to be reigned in every time it occurs, and by continually smoothing them out, music starts to lose excitement, dynamics, and even "feel" to a certain extent.
This is a cool thread, I'm looking forward to seeing where it goes... what RO members think. ;)
-d.

a transient is the leading edge of a sound impulse. it's not that hard to understand. some amplifiers (read as op amps or discreet amps) cope with transients better than others. older op amps / discreet amps have slower slew rates (how fast an amp can react to a transient) and they are usually deemed as inferior.

Slew rate is the maximum voltage change per unit time in a node of a circuit, due to limited current sink or source. The SR of a circuit is limited by its slowest node, i.e., the one with the smallest Slew rate.

transients are of the most concern to the recordist when dealing with compression attack settings. too fast of an attack can chop off a transient much like a noise gate that is triggering late cutting of the leading edge of the wave.

Speaking of gates cutting off the leading edge of waves...

The veterans in here already know this but, Sidechaining gates with a duplicate source track nudged forward a few milliseconds when looking to preserve the entire transient can be an effective transient tool/concept in the right situation.

I suspect that so much of the transient "smoothing" we hear these days is probably caused in large part by the easy access to tools that people now have in their DAWs. There was a time when - unless you had a pro level studio sporting a pro console that featured built-in, inline gain reduction on every channel/track return - that you didn't have 24 compressors in a rack, each one of which could be inserted in all your tracks individually. The most OB compression I ever personally had at one time was one LA2, one 1176, one dbx 163 and a rack of four stereo dbx 166's... Which sounds like a lot, but it wasn't enough to insert reduction on every track.
These days, in DAW land, you have a plethora of 3rd Party compressor plug ins to choose from, from at least 6 different manufacturers, and that's not even counting the processing you have that's stock/native to your DAW platform.
Do I like choices? Sure I do. But the other side of that coin is that you have mixers who - because they have 20 different compressors available - often feel the urge to use everything they've got, whether it's really needed or not. They use them pretty much just because they have them to use, thinking that every single one will serve a special purpose. The result is that they end up smoothing out all the transients of every instrument, and with that goes the energy and excitement of performances.
Another thing that is happening often is that those who are using drum samples are choosing samples that have already been compressed, and the first thing that these people reach for is a compressor to insert on the track where the sample is ... Effectively compressing a sample that's already been compressed. Then they add another compressor to the drums bus, and then insert more gain reduction of some kind on the master buss... Follow?
I don't want this to come off as a "rant" against compression - or gain reduction in any form - if I feel a track, bus or mix can benefit from it, then certainly, I'll use it. I don't happen to share Bruce Sweden's thoughts on gain reduction... Although I do like that he likes to preserve transients, but I'm not against using it like he is.
Like any audio tool, it can destroy the sonics of a mix just as easily as it can enhance them.
I'm not out to kill every transient I find. ;)
FWIW

One thing to mention is that the human ear perceives volume based on sustained sound. Probably part of what makes compression do alluring at first, as your reducing the impact for more sustain, hence volume.

Transients and headroom go hand and hand, as does adequate power and headroom in all/speaker situation. Like Kurt mentioned skew rate. That power is important both to help reduce distortion and to react nice and fast so your speaker jumps off the line like a high end sports car. A lot of people associate power with pure volume or loudness, but in the good systems it’s there for clarity. The transient response helps localize instruments and sounds within the sound field. I’m guessing it also creates a truer timbre as well due to less smearing.

Dynamic range and sesnsitivity are really important, to be able to really go from 0-10 quickly and capture the nuance.

I think across the board dynamic range, signal to nose ratio, and sensitivity, are crucial to anything in the audio chain, from conversion to mics to pres and speakers. High ratings in those areas will give a better transient response with less distortions, and more impact and clarity.

This isn’t to say that slow reacting or bandwidth limited gear isn’t cool. Rather to say that it’s an option to use with the more precise higher spec gear, and a limiting factor for other gear.

As soon as you push things into distortion your asking for reduced impact and phase/time related cancellations. It doesn’t have to be all bad. Tube guitar amps distort and compress nicely in even order harmonics.

In general it’s clear recordings that tend to stand the test of time, even in rock and roll. They often sound bigger.

Transient response really lends a lot of reality to recordings and systems.