Early in the King’s Singers’ Christmas concert at Washington National Cathedral on Saturday, the a cappella group performed a motet by Renaissance composer Adrian Willaert with the kind of seamless blend and pitch-perfect, liquid tone that could rival the sound of the Tallis Scholars, or any of the starriest early-music ensembles in the business. Given the glut of pop-crossover material this popular sextet has released over its 50-year history — including Cole Porter and Robert Johnson music as well as John Lennon’s and Billy Joel’s — it has, at times, been easy to forget what formidable experts they are at Renaissance polyphony. The King’s Singers’ personnel may have changed regularly since their founding in 1968. But in style and timbre they’ve remained remarkably consistent, grounded in the pure-voiced aesthetic of the Choir of King’s College, Cambridge, in which their founding members had been choral scholars.

That rarefied sound (subtly amplified at the Cathedral by a troika of mics) served them handsomely in an unhackneyed selection of yuletide music, highlighted by Bob Chilcott’s buoyant setting of a Maya Angelou text, “We Are,” and by Keith Roberts’s arrangement of “Carol of the Bells,” rich with vocal simulations of bell resonance and overtones. And, in a nod to their crossover repertoire, a set of inventively arranged Christmas songs allowed the Singers to channel the Swingle Singers, the Four Freshmen, the Manhattan Transfer and, in whimsically retooled versions of “Sleigh Ride” and “Jingle Bells,” the Comedian Harmonists. On a more sober note, a reading of a World War I soldier’s letter from the front, underscored by John Rutter’s version of “Silent Night,” proved a moving centennial tribute to the Great War.

Saturday was the final concert for retiring countertenor Timothy Wayne-Wright and baritone Christopher Gabbitas. But if the King’s Singers are true to form, they’ll be back with superb new soloists, sounding reassuringly like their old selves.