Inland a touch, at Snape, among the off-stage noise of the festival's building programme working its way through several million pounds of millennium funding, rising sopranos and mezzos in their twenties and thirties were biting great chunks out of the 20th-century song repertoire at the Britten-Pears School. Anyone can attend masterclasses at the school; it's cheap and easy. For the first time this year, in a brilliant innovation, three such singing sessions will be in the festival programme, so this felt doubly like a rehearsal.
There is nothing like watching singers exploring their anxieties about performing this tough music to blow away your own fears about listening to it. It helped that few of these 12 professional or postgraduate singers (most of whom, like the two teachers, are from the US) knew how to make an ugly noise. They took the music of George Crumb, Cathy Berberian and John Cage and could show any sceptic that there is loveliness there.
Singers are notoriously neurotic, and modern song is not normally regarded as easeful, yet the miracle of attending these classes was that they were workmanlike, fun and moving. The young women surprised themselves by not competing with one another - an experiment in singing like divas but not behaving like prima donnas.
Phyllis Bryn-Julson, whose earlier career pioneered much of this material, has done seven annual stints at this job. She tells the accompanists where Messiaen himself ran out of fingers to play the notes, or where the song can be taken much more slowly than is written on the page. "That may be what the score says, but it's not what we worked out at the time," she says, with the authority of having worked with Boulez, Lutoslawski and Ligeti.
She appeared to combine showmanship with a delight in technicality. A singer said at one point that she wanted to relax a little in a particular passage. "But Messiaen didn't want you to," came back the icy oracle. "You watch that rhythm: you get just as many chills from rhythmic accuracy as you do from timbre."
Her confidence was inspirational, a real issue with material that so often requires a performer to blast off disjointed noises into deathly silence or an apparent chaos of other sounds. Cari Burdett, one of several spectacularly tall, super-model singers on the course, wanted help with an electronic piece. Bryn-Julson remarked: "Go back and study Monteverdi when preparing this stuff: remember the classical repertoire. For every electronic piece, there's a Donizetti song you can use as a security blanket." Kristen Toedtman (a great chanteuse in Weill) repeated another Bryn-Julson message: "You need to keep some Schubert in your Milton Babbitt and put some Messiaen into your Puccini."
This cross-over approach - taking the existential to the mellifluous, and the melodious to the exiguous - is a key to finding the loveliness in modern song (and nicely supposes that the compliment can be repaid by the older music). One begins to see that modern composers keep much more truly - and tunefully - to traditions in song-making than at first appears - and only partially because they often use old texts. To test the truth of this, try playing the Schubert and the Britten CDs by the tenor Ian Bostridge - the better, at least, to overcome the disappointment that this singer's recital of both composers at this year's festival has been fully booked for weeks.
Singers of modern song have to be technically highly proficient. The range and rapidity of changes of tone are awesome. A composer will take a melody and put whole octave jumps into it. The tune is there, but it's as if it's on stilts. And the singers say they have to count beats with great accuracy. Finally, you have to love the words. Mangle them, and Bryn-Julson mangles you.
The mechanics of singing are exciting, and are never better demonstrated than in these stripped-down, interrupted performances (they remind you of a blues guitarist playing unplugged).
Singers go to vocal consultants as well as teachers, and live at constant risk, like athletes. At the Britten-Pears School, Ruth Drucker, a long- time friend of Bryn-Julson, takes care of this side of things. "See," she shows Emily Strode, an English mezzo, placing the singer's hand on her own stomach as she demonstrates a note: "I want it from here." And then, with another student: "Yes, that's better; we need the sound to come from higher up", as she discusses a quality of note to be wrung from the youngster's head. "A little lift in the mouth, a little smile, does the trick."
They are chasing sounds all over the place, unearthing them in bits of the cranium, getting them out better by imagining a wire suspending them from the top of the head. These singers' bones matter as much as their brains.
"We are neurotic because we are our instrument," says Christa Pfeiffer, not that the toll shows in her wonderful composure on stage. Cari Barrett gives the biggest clue as to how emotional things become: she dissolves into tears in one passage during a vocal workout. It appears that the noise she was making had unlocked an animal response. People wail when they're upset; this was just a very composed howling. By the way, Bryn- Julson strongly recommends lovers and childbearing for young singers seeking extra quality of tone.
"You have to be prepared to be vulnerable," says Pfeiffer. "Getting good means being able to bare your soul." It also means, oddly, staying uninvolved: this is performance, after all, and control and technique matter hugely. Bryn-Julson is always ticking the women off for being either "too Broadway", or "not Broadway enough": they have to be able to be austere, flashy, haughty and unhinged by turns - and all on tap.
Bryn-Julson and Drucker appear to work hardest on getting the youngsters to slow down, to make less noise. "Let the audience do your work for you," says Drucker sternly to one woman. "They like to do that best. Let them complete the work." She knows that it's leaving well alone that brings audiences to the edge of their seats. "Give the audience more time," says Bryn-Julson, wryly: "They need to recover between onslaughts."
To one woman daunted by a difficult passage, Bryn-Julson's advice is: "You did yourself in with the negative thoughts. There's always a limit to what the voice will do. But stay tall. Anything negative shows. And go and find a Bellini song that goes to the same place. Find that sound and put it into your voice."
It sounded like remembering to pack the right clothes, or remembering the right tools for a plumber to take on a job. It also sounded easy, which is rather the point.
Aldeburgh Festival, 11-27 June. The BPS Masterclasses with Roger Vignoles are on 15, 16 & 17 June, with a concert by BPS alumni on 18 June. Box office: 01728 453543.