All About That Bass Drum? Asynchrony Effects on the Perceived Timing of Compound Musical Sounds

When a sound occurs (i.e., its acoustic onset) is not the same as when we perceive that sound to occur. The latter location is known as the "P-center" in both music and language perception, and can be a few to over a hundred milliseconds after a sound's acoustic onset. While P-center perception in music has received scrutiny, it remains unclear how P-centers emerge when multiple instruments play together, particularly when they are not perfectly synchronized. Here, we investigate the effect of different degrees of instrument asynchrony on the P-center of their combined sound. In two experiments, participants aligned a click probe to pairs of instruments used in popular music with varying asynchronies (0-±80 ms). Results show that increasing asynchrony shifts the P-center of the compound sound later in time. Moreover, fast-attack instruments (e.g., kick drum) exert a strong pull on the P-center; fast-slow pairs largely retained a single P-center anchored to the fast-attack sound. By contrast, pairs of fast-attack sounds with ≥40 ms asynchronies between their individual P-centers provided evidence of perceptual segregation of the sound into two events. The findings show how inter-instrument asynchronies and attack characteristics jointly structure the perceived timing and unity of compound musical sounds.