If you’ve ever watched a vocal talent show such as American Idol, you might have noticed: when a judge claims a contestant is “pitchy” or “out of tune,” the audience tends to disagree. Nothing will set off the boos faster than Randy Jackson claiming a performance was “a little pitchy.”

So what’s going on there? Is the judge simply wrong? Or is the audience giving the contestant more credit than she or he deserves?

A team of researchers led by Sean Hutchins has devised a clever study to see just how out of tune a singer can be before listeners take notice.

But the team also did something else: Singers aren’t the only musicians who can be out of tune. Many string instruments, such as violins, require the musician to tune each note as it is played. Hutchins’ team wanted to know if listeners could tell when a violin was out of tune as well.

The researchers asked volunteers to listen to short “melodies” such as the following:

In each case, the task was to decide if the last note played was in tune or out of tune. The melodies in this post (which we created using a software simulator) are similar to what the researchers used, except they recorded actual performances by a violinist and a mezzo-soprano. Then they systematically varied the final note and asked listeners to say whether it was in tune. Here’s a sampling of the results:

This graph shows the percentage of the time listeners correctly indicate that a note is out of tune. Very few non-musician listeners could tell when a note was off by 10 cents (a musical “cent” is 1/100 of the difference between each of the keys on a piano). As the notes were performed more and more out of tune, more and more listeners could hear that something was wrong. But curiously, significantly fewer listeners said that a note sung by a singer was wrong, compared to a note played on the violin at the exact same pitch.

By the time notes were performed a full 50 cents out of tune, most listeners correctly indicated that the violin was out of tune. But most people still said the vocalist was in tune. When a note is 50 cents off, that corresponds to a half of a semitone — the difference between the white and black keys on a piano. In other words, the singer was performing entirely the wrong note, but most listeners still thought it sounded fine.

So listeners seem to be more generous to singers than to other musicians: When a note is sung out of tune, they are significantly more likely to say the singer is in tune than a violinist. The effect persists even when the listeners are trained musicians. The musicians are better at telling whether a given note is in tune, but are still more generous to a singing performance than a note played on the violin.

The researchers call it the vocal generosity effect.

By the way, in the example we provided above, the final note in the second (violin) and fourth (vocal) melody was off by 30 cents, so that gives you some sense of the type of musical error that most listeners don’t detect, especially when sung by a vocalist.

Why might this be? Hutchins and his colleagues are careful to point out that this study doesn’t tell us. But one possibility is that when we hear a human voice, our perceptual system moves in to a “vocal mode” that pays less attention to pitch.

Hutchins, S., Roquet, C., & Peretz, I. (2012). The Vocal Generosity Effect: How Bad Can Your Singing Be? Music Perception: An Interdisciplinary Journal, 30 (2), 147-159 DOI: 10.1525/MP.2012.30.2.147