Paris, France. Likely the The Palais Garnier.
Present day. Searched:
Variations on "white-tie," "premiere", "first-night", "theater", and "opera" with "appropriate attire" and "dress-code." Also searched for music venues in France, and read through the Wikipedia articles for each, visited the sites for each, but still in quandary.
1: A famed violinist is giving the last performance of his career in Paris. He's a bit of a traditionalist, and his standards for his venue (especially the acoustics) are as high as you might imagine. Would the Palais Garnier be the best choice available to him in the city, or is there another venue (in Paris, or elsewhere in France) that possesses better acoustics or would be more appropriate to someone of his status?
2:A female character is expected to attend the aforementioned concert (for the moment, assume at the Palais Garnier.) The event is white-tie, and it's critical that she be irreproachably garbed for the occasion, since she is attending on sufferance. Searches have turned up lots of information about men's dress, but for women I keep finding the less-informative "ballgown" or "evening formal dress."
Maybe this isn't as confusing as I'm making it, but --what does "ballgown" mean in a modern context? I know the standard in historical periods: during the Regency (for example) a woman would not
wear a ballgown to the theater: she'd wear a gown-for-going-to-the-theater, which had totally different standards of design and didn't need to look good on the move.
So: what does "ballgown" mean here?
ETA: Here "irreproachably garbed" does not mean "Cinderella fantasy." Actually, quite the opposite: she needs to meet the standards of the event and do so stylishly, but also discreetly. If anyone notices her for her costume, and remembers her long enough to come find out her name, she'll have done it wrong.
Son of Edit: Female protagonist is thirty --so not quite Barbara Walters territory, but definitely not going to want to wear what the starlets are wearing.