Stern is the son of Issac Stern, the late violinist who introduced the world to Chinese classical musicians with his Oscar-winning 1981 documentary From Mao to Mozart. He seems to be following in his father's footsteps. Since 1999, he's been a regular collaborator with Chinese orchestras and events such as the Beijing Music Festival.

At the moment, however, he's busy rehearsing Faust's 140 musicians, including some 60 members of the Hong Kong Opera Society Chorus, more than 60 members of the Hong Kong Sinfonietta and soloists from the US, New Zealand, Wales, South Korea and France.

Lo oversees the entire operation, including lighting by Leo Cheung Kwok-wing, costumes by Mandy Tam Ka-yee and sets by Charfi Hung Ho-yan. Tam and Hung are twenty-something graduates of the Hong Kong Academy for Performing Arts, which Lo ran until his retirement, a few weeks ago. 'I have a very special feeling for the APA and its graduates,' he says. 'I want to let Hongkongers do as much as they can in my productions.'

Gournod's Faust has been performed in all sorts of forms and interpretations, but Lo wants to stage it during first world war. 'I'm not doing it as a gimmick,' he says. 'I chose [the era] because it was the first time the world saw mass killings in war like that. But I didn't want to choose something too recent, because the production would lose its stage impact. The underlying message is that nobody wins in war.'

Although there are only two weeks for rehearsals, Lo started production meetings three or four months ago. 'They're professionals and know to do research before they start,' he says. 'They research the story, read the text and listen to CDs. My job is to tell them exactly how I want to develop the story.'

Lo has briefed them on a more modern approach to costumes and sets, which he wants to be 'free from the constraints of the story's history'. Tam has drawn up detailed sketches of costumes for each character, which she'll create with fabrics she dyes herself. Hung has created scale models of the sets, which Cheung has lit with mock-lighting.

Because Hong Kong doesn't have a full-time opera house, the $2.5 million government-funded Faust and other local productions have to be made from scratch each time. There's no full-time opera company with a ready-made designer, crew, orchestra and chorus.

'It's tough,' says Stern. 'I have to rehearse two full casts through a two-and-a-half-hour opera in two weeks. I've known European opera directors who have spent three hours just working one gesture of the hand.'

He says rehearsals are going well, although improvements can still be made. 'The two local singers [mezzo-soprano Melody Sze and bass Pong Chung-lam] have good voices, but they have a long way to go in terms of understanding the French language,' he says.

What's the greatest hurdle for young Asian singers? Stern answers with a singular rolled 'rrrrr' - the bane of many non-French and Italian singers. 'Only after we get past those technicalities can we work on making the music beautiful,' he says. 'And after that, we have to get them singing while dealing with all the costume changes, props, acting and staging. It's a huge amount for them to learn. I wish I had a week with each of them.'

The Hong Kong Opera Society Chorus is made up of part-time singers. 'They lack the solidarity of a chorus that sings 25 operas a year together,' Stern says. 'But they put so much energy into it. If the performers aren't happy to be there, then the show becomes a bore, no matter how technically good they are. These people are happy and eager to learn.

'When you have 65 people in the pit and 100 on stage, something's bound to go wrong, in any city. Maybe only for a few moments each performance, everything's perfect.

'But sometimes, when the right lights are on, the singer is standing the right place, he's singing the right notes and he's singing well, then it's amazing.'

Faust: An Opera in Five Acts, Thu-Sep 20, 7.30pm, HK Cultural Centre Grand Theatre, $120, $240, $360, $500, $650, Urbtix.