Possible Clues:

• Groan at ridiculous gradient going up on stage without any preparation
• Sense scanning is for performance without prior coaching
• Take a deep breath before walking on - it's a skill acquired by musicians
• Take a breath on ridiculous gradient going on the stage without any preparation
• Playing music you've never practiced (... 5 to 9)
• Veteran musician's skill
• Grade in this incredibly good, looking at score
• Take a breath on ridiculous gradient taking to the stage without any preparation
• Musician's skill rescued tarnished gig
• Performing without preparation, I'd turned up in odd gatherings