Possible Clues:

• A musician performing without preparation
• Expression of despair by pedestrian performer allowed no rehearsal?
• Gifted musician cracked head register, losing a repeated note
• Very able musician
• Expression of boredom, given pedestrian notes he hasn't studied before
• Expression of resignation by plodder, one quick to know the score
• Versatile musician
• One immediately knows the score with pacer after sign of exhaustion
• Music follower's show of apathy with the pedestrian