tough sounds to reproduce ???

Sean there are too many to mention. As Albert notes the sound of a marching band as it passes. It is about impossible to get even close to the immediacy, dynamics and sense of each individual instrument. I never heard an audio system come even close. Funny Albert mentions it as I always get the same feeling everytime I hear a live marching band.

Also as Dweller notes the transition of the operatic soprano voice. It is just murder getting that the way you hear it live. As Sugarbrie notes, piano is tough also. My conclusions are a bit different though feeling the upper registers are the toughest to get right, generally seem to lack the air and presence that you hear from a live piano.

So far as thunder I have an excellent recording on Telarc with Kunzel and Cinncinati Pops Overture to "Phantom of the Opera". The opening involves a frantic woman walking in the rain with cracks of thunder in the background. It appears she is being followed. There is a dramatic increased pulsing of her heart as she walks faster. Cats screeching and heavy doors closing with the climatic scream and fall into the abyss as the organ opens the overture. It is VERY well recorded with some interesting sound effects. The decay of the thunder goes on to infinity, just like it really does. Other than the absolute volume of real thunder, the dynamics and sense of space are quite believable.

To add to Tubegroovers's comment , the upper registers of the piano is tough to reproduce since mostly it lacks BODY and WEIGHT of the real thing. Real sound does not just float! Lower ones are the ones could be produced convincingly in a full range-warm system.

brass blatt

Nil...huh?
I have my Steinway B positioned between and a few feet behind my Parsifal Encores. I hear GREAT piano upper octaves from my EMC-1 MkII/AlephP/Aleph2s?Encore system.
It's the LOWER octaves that aren't the same!
A grand piano's upper octaves DON"T have "body and weight".
Quite the contrary. They're thin, short, and basically excite only a small portion of the soundboard.
The bass strings excite the entire soundboard, and thus launch a HUGE pressurewave into the room which no reasonable number of speaker transducers can replicate.
Although I enjoy full-scale piano recordings on my system
(Nojima's Liszt on RefRec comes to mind as a great one), it's not the same as sitting down and exciting a giant diaphragm when I stretch out on those big Brahms chords.
Additionally, the top octaves' propagation toward the player or listener is VERY variable as a function of listening position, head angle, lid geometry, etc.
The ONLY way my B sounds right in the upper octaves to me WHWEN PLAYING it in my room is when the lid is fully shut, but the front door is wide open, yielding a constant depth
full-width "window" or port, if you will.
Sorry to belabor this, but getting a great system to do piano top octaves is not that hard. Voicing the damned piano is MUCH harder! Cheers.

Why didn't anyone mention violins in a symphonic orchestra. When many of these are playing together I find this the most difficult to reproduce. I always listen to violins when auditioning new equipment and it quickly gives me a sense of how good the product is.