With more than 50 albums to their name, five Grammy awards, and a large base of die-hard fans spread around the world, something has been going very right for the Swingle Singers for a long time.

What accounts for the a cappella group’s extraordinary success over almost half a century? Put it down above all to impeccable professionalism and the enduring aim of keeping everything fresh, varied, and balanced. Some 80 artists have been members of the Swingle Singers since their formation in 1962, and the current eight-piece lineup has an equal number of male and female voices—two basses, two tenors, two altos, and two sopranos.

The music covers a vast spectrum, from classical and world to jazz, pop, and experimental rock. Not surprisingly, the repertoire is extensive, and divided into several programs. Classical Reinventions, the show the Swingle Singers are bringing to MusicFest Vancouver, includes such unlikely bedfellows as Nikolai Rimsky-Korsakov’s “Flight of the Bumblebee”, Björk’s “Unravel”, and the traditional Turkish song “Gemiler Giresuna”.

It’s the group’s amazing vocal dexterity and infectious sense of fun that ties all the songs together. “We like to play stylistically,” says Oliver Griffiths, who joined the Swingle Singers last summer, reached in London where they’re based. “So even if a piece is originally a pop or rock song it may well not end up sounding that way. We want to try something different with it rather than doing a straight cover. That’s the exciting part for us.”

The arrangements come from several sources. “Two or three members of the group work things out regularly for us. And we have friends from around the world who’ll arrange as well. Plus there’s a massive back catalogue of arrangements from the last 50 years of Swingle history that we can turn to, and often do.”

A hallmark of the Swingle Singers sound has always been the use of voices as percussion and bass instruments, and the richness and closeness of the multipart harmonies, often jazz-based. But not everything needs to be carefully worked out in advance. “There are a number of moments where there’ll be a breakdown with the vocal percussion, and one or more singers will improvise,” says Griffiths. “So although our arrangements and structure are very tight and well-rehearsed, individuals can play with the music.”

The Swingle Singers all enjoy sharing the vocal roles. “Because there are eight of us we can be quite versatile about where the harmony, the melody, and the rhythm is. So on some songs the women beatbox and do the percussive stuff and the men take solos. Obviously we have two guys who are the drum and bass predominantly, and then the harmony and melody are split between the tenors, altos, and sopranos. But we all do a bit of everything really—it’s well-balanced, and we love that.”

The Swingle Singers perform Classic Reinventions at the Chan Centre for the Performing Arts next Saturday (August 6).