St Andrews Voices is young yet - the third annual edition opens next week - but as Scotland's first and only festival dedicated exclusively to vocal music it already has its niche in the classical calendar.

It has a strong footing in St Andrews, too.

"There is a huge appetite for singing in this town," says Sonia Stevenson, the festival's co-founder and artistic co-director. She points out St Andrews Chorus is the largest choral society in Scotland and that the university's top choir, St Salvator's, is now good enough to rival the iconic chapel choirs of Oxford and Cambridge.

"The enthusiasm and knowledge among the festival audience is extraordinarily high," she says. "Almost everyone who comes along is a singer of some description themselves." Incidentally, she defines 'singer' as anybody who hums a tune in the shower, but the point stands: St Andrews is a well-versed crowd.

Stevenson's programming tack is simple enough: her intention - and that of her co-director Michael Downes, head of music as St Andrews University - is to present a diverse and classy showcase of vocal music. As yet the range is still fairly orthodox, but she hopes to broaden the scope in future.

This year there is a recital by the revered baritone Roderick Williams, who sings Ivor Gurney, Britten and Schubert with Scottish pianist Iain Burnside. There is a programme of operatic arias from soprano Stephanie Corley, tenor Ji-Min Park and baritone Marcus Fansworth; a Bach cantata ('Wir danken dir, Gott') sung by the aforementioned very good St Salvator's; afternoon of cream tea and vintage jazz with BBC Radio 2 favourite Martyna Wren.

To close the weekend, the Scottish Chamber Orchestra Chorus performs Brahms's A German Requiem - great paean of choral writing - in the composer's own version with piano duet instead of orchestra.

Newcomer to the festival and potential highlight of this year's four-day line-up is the young Marian Consort, directed by Edinburgh-born countertenor Rory McCleery. This is undoubtedly an ensemble to listen out for: where The Sixteen performed at St Andrews Voices last year, Stevenson says this year she wanted to recognise the wealth of "equally brilliant" young vocal talent from the UK. The Marian Consort was her pick of the bunch.

The group's speciality is renaissance sacred music: its name refers to the Virgin Mary, subject of some of the most sublime devotional music of the period. Its recordings for the Scottish label Delphian have so far featured music from the Spanish renaissance, from the Dow partbooks and the 16th century French composer Jean Maillard.

These recordings are impressive. The Marian sound is refined, clear and shapely, with a one- per-part lightness and a scholarly hand from McCleery that is authoritative but not stuffy. As a boy McCleery was a chorister at St Mary's Cathedral, Edinburgh; now in his late 20s, he is completing a PhD on the music of the French composer Jean Mouton and co-editing Mouton's motets for a forthcoming complete critical edition of the composer's music. His easy familiarity with the repertoire is evident in every gently sculpted phrase, every finely-controlled line of polyphony.

McCleery founded the Marian Consort when he was still in his second year of an Oxford undergraduate music degree - "it was the slightly hapless result of total naivety on my part and a genuine passion for singing this music," he remembers. He gathered together a few fellow choral scholars and organised a concert that included two of the masterpieces of the 16th century: John Sheppard's Media Vita and Robert White's Lamentations. "That was absolutely mad," he says, with a laugh. "I would never, ever try to programme two such big works in the same concert now."

But the group survived the challenge and has since made a name as one of the UK's brightest young vocal ensembles. McCleery acknowledges its heritage is the very smooth, chaste-sounding Oxbridge choral tradition: "a strong label that carries certain connotations," he says, "perhaps of a slightly generic, anonymous, esoteric and always beautiful blend." All of which can be well and good, but is not exactly what he is going for.

"Even if we wanted to we could not fully achieve that big, slightly pastel blend - not with one singer per part. Our small forces mean the individual quality of each voice really shines through."

On the matter of historically-informed performance he is basically a pragmatist. "We do not know what a 16th century choir sounded like, but it was probably terrible," he says, attributing the quip to the Tallis Scholars' Peter Phillips.

"There are records of singers of the Sistine Chapel getting fired for turning up drunk, for starting on the wrong note and so on. I think that gives us licence enough to phrase according to our tastes. Sure, we pay attention to subtle differences in text: the particular pronunciation of Latin in Spanish music versus French or English or Flemish music, for example."

When it comes to tuning systems - a juicily contentious subject for early music aficionados - he shrugs. "The beauty of a-cappella music is we are not reliant on any fixed tuning instruments. We can colour intervals in the way we want. Our relationship to the source material is veneration, but not slavish. We are not in the business of period-costume recreation."

The Marion's latest disc is just out - a Christmas album of sorts, comprising 16th century music by Jean Mouton and others - and in January the singers will be back in front of the microphone to record music from John Baldwin's Tudor partbooks, a sequel to the Dow album.

Before that, though, is St Andrews Voices and a programme of intriguingly mixed fare. Asking the Marian Consort to sing the music of Jonathan Harvey was the idea of Sonia Stevenson, who had worked with the British composer in her previous job with the publishers Faber & Faber.

"The deepness of his vision, his profound spirituality, the fact he had been a chorister and so grew up in the Christian choral tradition but became a Buddhist and had a real breadth of cultural feeling ... Harvey's choral style is beautifully simple, a voice that rings true," says Stevenson.

Set among the ancient music of Tomas Luis de Victoria, Palestrina and Mouton will be the Scottish premiere of Harvey's The Annunciation, an incredibly powerful work composed shortly before the composer died of motor neuron disease in 2012. It is a bold piece of programming, and should be the ideal showcase for the Marion Consort.

St Andrews Voices is October 23-26; The Marian Consort's latest album Christmas with the Shepherds is out now on Delphian