“The Sound of Mumbai,” premiering tonight on HBO2, is a touching documentary about the most unlikely of productions, a concert performance of “The Sound of Music” featuring the “slumdog” children of one of the poorest communities in India.  These children have so little contact with the world outside that they had to be shown a photograph of a mountain to understand what “Climb Ev’ry Mountain” was about.  But they thrilled to the music of Rodgers and Hammerstein and the opportunity to perform in front of an audience.  I spoke to director Sarah McCarthy about making the film and a young singer named Anish whose confidence and spirit are especially endearing.

Does everyone in the audience cry when they see this movie?

Lots of people do.  The sniffling in the theater when Ashish sings his solo, and then others hold out until the end.

It was interesting that the conductor was an Austrian.  It was a culture shock for him.  How did he feel about working with songs set in Austria but written by Americans, about a family that escaped from Austria?

He was invited because of the connection with “The Sound of Music” and he really didn’t know what to expect.  He was kind of overwhelmed by the whole experience of the slums and running around with Ashish and seeing how the kids live, about how they sleep on the floor and about how one of them was nearly sold for adoption and he couldn’t really believe it.  He’s talking about going back in a year or so.  It was an extraordinary and overwhelming experience for him.

I think Austrians have mixed feelings about the show, “The Sound of Music” because they were compliant with the Nazis.  The first production they have ever put on in Salzburg is going on at the moment.  For a long time they rejected it and it’s only now that the new generation is embracing what is, after all, the biggest musical of all time.

How did you come to this project?

My producer, Joe Walters, sometimes conducts the Bombay Chamber Orchestra and was always at me me to make a film about it and I thought that sounded really boring.  He sent me the announcements of the concerts they were doing and one was about children from the slums singing songs from “The Sound of Music.”  My ears really pricked up because I thought how strange to hear these iconic songs that make you think of mountains and green space and rivers sung by these kids — that audio/visual disconnect would be quite cool for your brain to try to make sense of.  Off we went to India and made a trailer and fell deeply and instantly in love with every one of the kids.  We came back to London to try to raise money, failed, and went back anyway, with the tiniest most ridiculous budget, running out of money on the shoot and working off of credit cards.  It wasn’t until we showed the film at the Toronto Film Festival and sold it to HBO that I could pay our cameraman.

What is your background?

I’m Australian and went to film school in Australia and then came to London and worked in development at the BBC and an independent channel.  I made a movie called “Murderers on the Dance Floor” about the 1500 inmates at the maximum security prison who performed to Michael Jackson’s “Thriller” and became an internet sensation.  The prison governor is really deranged.  They practiced 8 or 9 hours a day.  He also had them do Vanilla Ice’s “Ice Ice Baby!”  Then I made a film for the BBC about a 77-year-old “killer granny” who killed her husbands for the life insurance money. I’ve just come back from a month-long shoot in Russia and the US about an American family that adopted three Russian children.

How did Ashish become so confident?

It comes from his family unit.  He’s genetically engineered to be that way but his mom and dad and brothers and sister are very close-knit.  Those places can be dark and dangerous but they all live on top of one another and have to learn to be friends.  There’s a real community there and the kids thrive on that.  I was blown away by how socially sophisticated these kids were.  These kids have a close family but not a safe place to live or enough to eat.  The kids in my next film have had a safe place to live but no family ties or community.  Ashish’s school is also very encouraging, though they’re not academically rigorous.  It’s pretty tough to be on such minimal resources.  That is the biggest struggle for us.  We’re interested in using the film to further these kids’ education.  We’re working with the school to raise funds to put these kids through university but they also need to catch-up support to be able to do the work.  We talked about putting him in a different school but decided it would be too tough for him.  They don’t have the basics — a quiet place to study, a structured lesson plan, a desk.  You can have all the determination and commitment in the world and it is still really hard.

Ashish has moved to a better place.  He now lives in an apartment with a door that locks and a tap he shares only with about 30 people instead of 300.

How did you gain the trust of the kids so they could be so candid with you?

I have two younger brothers.  And I love kids.  I love hanging out with them.  Ashsish and I became friends very quickly and played a lot of games.  He almost became part of our crew.  I’m in touch with him all the time.  We Skype at the school principal’s office and I remind him not to show off and brag all the time.  But he remembers that concert very clearly.  He snuck into his neighbor’s apartment and watched it three times in a row.

HBO’s teachers guide is available for download.