For some background, artists, labels, and producers usually have some degree of control over their volume levels during the mastering process, a process of putting the final touches on most albums. But Spotify and other streaming services will also “normalize” volumes. In most cases, streaming services normalize each song submitted in order to provide the listener with a more even experience. But the process of normalization is a bit of a black box. Even mastering engineers don’t really know the full details of how each song is normalized by each streaming service.

Normalization can really affect listeners’ experiences. Bass response is higher at louder volumes, so music can feel more resonant and powerful when it’s louder. Quieter songs can sound thinner and more hollow. Consistently, listeners will rate music as better when it’s played at a louder volume. When users are making their playlists, quieter songs might sound weaker, meaning that, by affecting normalization algorithms, Spotify could be making it much harder for unsigned artists to gain a foothold in playlist placements.

Could a difference in mastering techniques account for the volume difference? Maybe so, but we restricted our analysis to unsigned artists who had used a reputable mastering service. The services we included were: Masterdisk, Bernie Grundman, Abbey Road, Sterling Sound, and The Mastering Lab. These all seemed to be well-regarded mastering services that conform to industry standards for mastering. For full disclosure, we evaluated only a small fraction of the millions of songs that have been published, so it’s hard to say that our findings are exhaustive, or that these conclusions definitely apply across all music. Still, this obvious disparity seems suspicious.

This conversation started when we heard from a lot of local bands that their songs were quiet on Spotify. It turns out this wasn’t an isolated complaint. Reddit posts and posts on other messaging boards echo similar sentiments. A lot of unsigned artists have voiced this concern on social media platforms as well.

To anyone in music, it’s no secret that Spotify makes it harder for independent artists to succeed. For one thing, Spotify has come under fire for paying artists pennies or less for thousands of streams. Even artists with millions of streams on Spotify have complained about the low rate of musician compensation. Also, most people on Spotify discover music through editorial playlists and other Spotify-curated playlists. Artists can submit their music for editorial playlist consideration, but most spots on Spotify-curated editorial playlists are occupied by artists on major labels.

Although there are numerous complaints by artists about Spotify and other streaming platforms, we found that this issue of loudness hasn’t been widely discussed by the music industry. It’s getting harder and harder to gain recognition and earn a living wage as an artist. While streaming platforms can help musicians expose their music to a wider public, Spotify seems to be stacking the odds against unsigned artists.