??? My First Classical Concert,What Can I Expect ???

Brandenburgs are a staple for "classical" orchestras, but remember it is a BAROQUE composition. A lot depends on the execution:

- Harpsicord should be used, but sometimes the dreaded piano is substituted. Harpsichord (and lute/theorbo) are part of the rhythmic section (aka basso continuo, akin the drum kit in a rock concert). The sharp attack of the plucked harpsichord helps with that, while the smeared sound of a piano obfuscates this key function.

- Authentic strings are played on gut strings and at 415 Hz, but very few orchestras do so. Gut strings have a completely different sound to modern synthetic ones.

- Playing technique in classical orchestras uses vibrato as a sauce, while in proper execution it is an ornament (rank 13 according to Bach). The main ornament are variations on the trill, so listen for variety of trills used (starting on upper/lower note, speed, acceleration or not, ending in a turn or not). Those are not written into the music and are improvised to taste by the musician.

- If you are lucky enough to hear a period orchestra perform it, they will also use a baroque bow (outward curved, not inward as in the classical Tourte bow), which helps with note shaping/messa di voce critical for baroque music to shine. How much that is smeared by the typically reverb-heavy acoustics of a church is an entirely different question. Brandenburgs are rather a da camera piece (to be played in a room), not da chiesa (church music). Accordingly, playing Brandenburgs in a church is a questionable choice.

- Lute/theorbo is typically too quiet for large venues such as 500 seat church, and has to be amplified. (frequently also the harpsichord(s). 

- Repeats are elaborated, but elaborations are not written out. So listen for the type and artistry of the elaboration on the second pass.

Baroque music frequently gets a bad wrap ("acquired taste"). That stems mainly from the mostly poor execution (piano/harpsichord, vibrato sauce, etc.). I heard once a Haydn performance where the keyboardist for one used a piano, and played the bass line (aka figured bass) as single notes, not realizing that a chord is tastefully improvised in Baroque music. I hope you will hear a good performance.

I disagree it’s most of what is written above.  So you won’t see anyone lighting their  violins on fire or being lifted by a cable over the audience.

  The Brandenburg Concertos feature a lot of instrumental effects.  For example the Sixth omits violins and uses low strings only.  The Second features a very high-piccolo- trumpet that Paul McCartney liked so much when he heard it he adopted it for Penny Lane.  The Fifth is basically a harpsichord concerto in the first movement, that ends with a crazy cadenza (solo) where Bach was foreshadowing the Piano Virtuosos 150 years in the future.  The second movement is basically a chamber outing between the flute, keyboard and violin where the 3 lines weave in and out as only Bach could do so seamlessly.

  Every concerto has something special.

  Listen to the music at least twice before the concert so that it has something special familiarity.  Then when you are there are how different choirs of instruments produce the sounds .

@d-o-tampa ,

" As a musical omnivore myself..."

Terrific description!

You will experience real sound stage. 
Hope you have good seats. 

I too went from rock concerts to classical.  Bach's Brandenbergs are a great place to start.  Forget critical listening and just let the music take over.  One bit of advice, if you're not familiar with classical concert etiquette--each of the concertos consists of three movements; most classical audiences do not applaud until the end of the whole piece, not after each movement.

Also, +1 to d-o-tampa.

Awesome you’re trying something new! A few things I’d recommend- check with the orchestra and see if they do pre-concert lectures. Most larger orchestras do these. A good chunk of these will play motifs and excerpts so you have some context when you hear the whole piece. That can be great if you’re new as you’ll then be able to pick out the important parts and then hear how melodies get thrown around and transformed across a piece.

Pick one instrument / person in your sight line and adopt them for the performance. This is great for critical listening, particularly if you’re not familiar with the instrument. Why is that good? You’ll generally find it’s like developing a new muscle- when you go home you’ll be able to pick and isolate that instrument on classical recordings when you get home. Then if you go back to another concert you can adopt another instrument and build more musical muscles.

Those are some quick tips. As a musical omnivore myself no musical genre is boring- it’s just a matter of learning to speak a new dialect and learning what each brings to the table, and ends up giving you a new experience to enrich your home genre.

Why?

I am envious, I think you will be enthralled.

My First Classical Concert,What Can I Expect
 

During a frantic passage, a trombone slide gets propelled with great velocity. Over the band, past the stage, row 1, row 2…until it hits someone in row 6 😉

I grew up on the same musical track as you and I think you are in for a treat.

Enjoy the experience.

I am more of an opera fan than classical music, but one thing I would do is really pay attention to the sound. I have been to hundreds of concerts as well and although some amplified concerts sounded great, nothing was close to an opera, a live jazz concert or big band jazz. Whether it was Woody Herman or Buddy Rich and their big bands or Bryn Terfel, Cecilia Bartoli or Joyce Didonato singing solo, live unamplified music is a must for all audiophiles, as it gives us a point of reference on what music actually sounds like.

Baroque is more of an acquired taste even for Classic music listeners. I am one. You might have a more uplifting experience with Mahler Symphony 1 or Stravinsky's Rite of Spring played by a big-name orchestra.

IME kind of boring compared to rock. But then when you listen for a while, you start to appreciate what they are doing. Historically dealers told me hi-end audio was for music like orchestra. I guess because you are listening for the quality of the musicians and not just the song itself.

I would be interested if you go into critical listening mode and if you can get yourself out of it. Also after listening will you like your stereo more or less than the real thing?