While recording Brass section in a small studio I have often noticed that the Brass section sounded fine through most of their Dynamic range
but became very thin sounding when played louder, especially Trombones. The Brass section most of the time will sound thin when recorded in a small room, even if played softly their lows will not have any definition and their high notes will sound shrill. First they will be sitting very close to each other so there is not much of air movement. They have to be played loud so you could get punch in their music. Recording in a big room gives that air. Their Dynamic range becomes wide. You can record the full section by just using stereo mic technique and that also not close micing. But most of our studio music rooms are small. I suggest hiring a good drama theatre and record them on stage. Try it out it and hear the results yourself !