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Listen to the following three short audio samples. Your job is to say whether the tempo (the rate at which the notes are played) is speeding up or slowing down. Even if it sounds like it’s maintaining the same tempo, make your best guess as to whether it’s speeding up or slowing down.
[Update: There's a new demo here. And see this correction]
Clip 1:
Clip 2:
Clip 3:
If the results here follow the pattern found in a number of studies, there should be a bias in the responses (and yes, some of the clips really are slowing down or speeding up). I’ll explain what’s supposed to happen later on in the post.
Music researcher Daniel Levitin (also a former music producer for acts like Carlos Santana and Blue Öyster Cult) has found, working with Perry Cook, that despite these biases in perceiving tempo for single notes, even untrained individuals have a remarkable memory for the tempo of songs they know well. They can sing them back, a capella, at almost precisely the same tempo as the recordings they hear on the radio.
If some studies have shown biases in the way we perceive tempo, then why are we so accurate with familiar songs? It’s probably not due to the subtle variations in tempo produced by artists: One study had pianists play songs at several different tempos — deliberately too slow or fast, then used a computer to speed up or slow down the tempo of the same music. Even musically trained listeners couldn’t tell the difference between the artificially sped-up music and music played faster by the musicians.
Sandra Quinn and Roger Watt recently explored the phenomenon using a different method, which I’ll discuss below.
They took 23 Scottish fiddle songs and played them on a synthesizer as marked in their musical scores. They then artificially slowed and speeded each tune’s tempo by 10, 20, and 30 beats per minute. Student volunteers listened to each song, as well as the original version, in random order (so they weren’t listening to the same song over and over again). They were simply asked if the song sounded too slow or too fast. This graph shows some of the results:
The graph charts the proportion of students saying each of three excerpts was “too fast.” As you might expect, the faster the excerpt was played, the more likely students were to rate it as too fast. But as you can see, for excerpt #1, a tempo of just over 60 beats per minute was rated too fast by nearly all listeners. Meanwhile, 100 beats per minute was seen as “too slow” for excerpt 24. Each song had its own ideal tempo, where half the listeners rated it too slow and half rated it as too fast. These ideal tempos ranged from a low of less than 50 beats per minute (as in Clip 1 above) up to well over 100 beats per minute (as in Clip 2 above).
An analysis of the measurable musical features of the songs found that most features (for example, whether the music was in a major or minor key) bore no significant relationship to the ideal tempo of the song. The only feature that did correlate significantly was the number of descending intervals, which correlated with tempo at r = 0.49.
So how is the optimal tempo picked?
Let’s return for a moment to the demo at the start of this post. It’s based on a 1978 study by Hans-Henning Schulze which found that people could accurately detect tempo changes — but only for single notes repeating at 100 beats per minute. Any faster [correctin: a 1997 study by Vos et al. finds], and even tempos were perceived as speeding up, while slower tempos were perceived as slowing down. The first of the three clips was played at 50 beats per minute and maintained a steady tempo. If we replicated Vos et al.’s results, most people should say this one slows. The second clip was again an even tempo: 200 beats per minute. Most people should say this one speeds up. The third clip starts off at 100 beats per minute. Respondents should have been able to accurately say whether it sped up or slowed down. I’ll leave discussion of that one for the comments section.
Do we have an internal clock that runs at 100 beats per minute? Quinn and Watt’s results suggest that if we do, we don’t apply it willy-nilly to every song we hear. Instead, something about content of the songs suggests an appropriate tempo. While their research doesn’t give us a definitive answer as to what that tempo might be, they do have some hunches. If a song has many “strong” events — events that vary simultaneously across several musical dimensions — then the authors suggest that these sorts of songs might be preferred at a slow tempo, compared to songs filled with weak events. Listeners want to savor those nuances, and can only do so when the song is played slowly enough.
Quinn, S., Watt, R. (2006). The perception of tempo in music. Perception, 35(2), 267-280. DOI: 10.1068/p5353
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