Excerpts are widely used to preview and promote musical works. Effective excerpts induce consumption of the source musical work and thus generate revenue. Yet, what makes an excerpt effective remains unexplored. We leverage a policy change by Apple that generates quasi-exogenous variation in the excerpts of songs in the iTunes Music Store to estimate that having a 60 second longer excerpt increases songs' unique monthly listeners by 5.4% on average, by 9.7% for lesser known songs, and by 11.1% for lesser known artists. This is comparable to the impact of being featured on the Spotify Global Top 50 playlist. We develop measures of musical repetition and unpredictability to examine information provision as a mechanism, and find that the demand-enhancing effect of longer excerpts is suppressed when they are repetitive, too predictable, or too unpredictable. Our findings support platforms' adoption of longer excerpts to improve content discovery and our measures can help inform excerpt selection in practice.