This new type of singing was assessed by different criteria, centred on conveying feeling, says McCracken. Technical considerations like projection or hitting high notes became less salient. "What becomes most important is that they sound sincere." Crooners weren't allowed to be anonymous voices performing for an audience. They had to seem authentic – and for that, they needed personality too.

An unwelcome development  

Like all cultural innovations, crooning had its critics. Traditionalists were horrified, with one cardinal publicly condemning the style as a "degenerate form of singing" and "imbecile slush" – even going so far as to criticise its perpetrators as "whiners and bleaters defiling the air". Established musicians and conservatoires weren't thrilled either: crooners were accused of lacking skill and corrupting the youth.

However, the crooners weren't finished, and the march of technology enabled musicians to push the style still further. The 1930s saw the development of directional microphones, a variety that pick up sound from a particular direction, minimising background noise. Singers who got close to those microphones discovered the 'proximity effect', which created an even more intimate tone, says McCracken. "People really liked that sound."

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With these new singing techniques came a new kind of celebrity. "Rudy Vallée was really the first pop idol," says McCracken. And along with this new lofty status came another invention: the adoring superfan. "The fan letters to him basically say, 'I don't know why I'm in love with the voice, I don't understand why this is happening to me.'"

The term crooning eventually fell out of fashion, but the trend still lingers in popular music today. "Anyone who's using popular music in order to communicate their emotions is crooning," says McCracken. “They're using microphones, they're singing love songs to a popular audience… that's what crooning is.”

We might imagine that people have always sung like Taylor Swift, or the contestants on Eurovision. But for most of history they didn’t. Singing as we now know it was invented in the 1920s.

Ubiquitous as the style now is, in those early days it seemed like a fad. One critic predicted, rather hopefully, that crooning would soon go the way of "tandem bicycles, mah jong and [miniature] golf". Given that all those things remain popular, he wasn't wrong.

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