The human voice is one of the most versatile musical instruments and can take forms as diverse as a heart-rending wail or a quiet whisper.
This weekend, hear these infinite shades of vocal colour and tone at the Voices festival at the Esplanade.
Esplanade programmer Christel Hon says the festival "celebrates the joy of ensemble singing and a sense of human connection through voice that is enjoyed by people around the world, regardless of culture, history or background".
The second edition of the festival will feature four headline acts - a local chamber choir and three international acts which are making their Singapore debut.
Ms Hon says "they represent the diversity of ensemble singing, stretching beyond the familiar formats of Western choral as well as a cappella singing which are already popular here".
Opening the festival on Friday night will be The Puppini Sisters, a trio who sing in close harmony - an arrangement of notes within a narrow range, a technique popular with groups in the 1940s and 1950s. It has been used by bands, including The Bee Gees, The Beach Boys and The Andrews Sisters.
Marcella Puppini, founder of the decade- old group, says she has been enthralled by the singing style since she was a tot.
She says: "I have been completely in love with close harmony since I was a baby, when my mum would send me to sleep with a record of The Swingle Singers doing Bach in harmony. This was my lullaby."
However, Puppini and the two other members of the London-based group - Kate Mullins and Emma Smith - do not just sing songs from the swing era. They have created their own blend which they call "swing pop".
Puppini says: "The kind of music we do is based on jazz and swing. But swing music, especially now, can get very serious. We're a little more playful and cheeky. We cover and rearrange a lot of pop songs as well."
For their concert here, they will be throwing in a few classics from the 1940s and 1950s, including Boogie Woogie Bugle Boy by The Andrews Sisters, and Mr Sandman by The Chordettes.
They will also be performing their own take on pop songs such as Blondie's Heart Of Glass and The Bangles' Walk Like An Egyptian, and self-penned original songs.
Puppini says of their originals: "They are humorous, light-hearted and sometimes cheeky. They're songs which are basically fun and resonate with the people who listen to us, like songs about being a millionaire."
The only local headline act for this year's edition of Voices will be Seasons: The Earth In Motion by One Chamber Choir.
The 30-member group, led by choral director Lim Ai Hooi, comprises mostly tertiary students and working adults.
Ms Lim says the small size of the group means that "the vocal technique has to be a bit more sound because there are fewer people per section".
She chose the theme of seasons as these "can be colour, can be emotions or can even be the season of life that we face".
The ensemble will be singing a variety of 20th-century choral music, such as The Snow by Elgar and When Sunny Gets Blue by Nat King Cole.
She adds: "I chose the songs to evoke emotions - not just things like happy or sad, but perhaps even fear, guilt or determination. I hope to trigger that reflection."