This is a great question!
I’ve had the chance to play and learn about being a professional musician in symphony and opera orchestras over the last couple of years, so I’m excited to share my thoughts.
To begin, I believe getting the music ready is quite similar. You need to know your part inside out, understand what it means in the bigger picture, and how it fits with the rest of the orchestra. For symphonic pieces, that’s usually all there is to it. However, when it comes to opera, there’s an extra layer of what’s happening on stage. I see my role as supporting the singers, which means being flexible and really paying attention to what’s going on.
When I’m playing in a pit instead of on stage, I try to bring warmth and clarity to my opera playing. I really concentrate on blending with my section and ensuring that those one-note “hits” have clear, strong fronts. Plus, I keep in mind that my main goal is to support the singers, so I avoid playing louder than necessary and instead listen to the conductor’s cues for dynamics. With that being said, I some experience with pitwork for musicals and in those times, i had more flexibility with dynamics because of the colors they invoke.
When I perform, I bring those same ideas to life, but I also emphasize projection and presence. Because the symphony is the star of the show, I can express dynamics more directly and with a wider range. I bring up presence because my instrument is a tool for the composer to achieve a specific color. So even when there are times when my part isn't the most prominent, it still has importance and needs to heard (and correctly balanced)
Last, since we have more space on stage, my Spidey senses are "on", to ensure I play in time with the baton and other instruments on stage. All that to say, I play louder

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Regarding Mahler 2, it’s important to really understand your part and how it works when you’re playing alongside the singers. Most importantly, don't overthink it. Trust in your preparation and approach rehearsals with a flexible mindset, ready to embrace whatever the stage presents.