A psychedelic light show pulses along with the music's hectic beat.

Dancers in the crowd point pocket lasers at the stage, and these events, in Cairo's toughest neighbourhoods, attract thousands of dancers. As the show closes, the performers jump from the stage into the crowd, showing their total identification with the people who have come to see them.

And when the music's over, and the crowd have left, the floor of the makeshift venue is littered with empty beer bottles, cigarette ends, clothes and the roaches of smoked-down joints.

This is mahraganat, the electro scene that has become the sound of young, working-class Egypt. Earlier this year, 20,000 mahraganat fans descended on Salam City, one of Cairo's densely populated and poor outer suburbs, for the wedding party of one of the movement's godfathers, Al-Sadat Mohamed Ahmed, aka DJ Sadat.

But while it's celebrated at street level, mahraganat - which means parties or festivals in Arabic - is disapproved of elsewhere in Egypt; it's seen as vulgar, the sound of the underclass. That's why you won't find it on Egyptian TV or radio, even if the shrill metallic notes of mahraganat are ubiquitous at weddings in working-class neighbourhoods, at massive block parties, from the speakers of taxis and tuk-tuks, or modest party boats on the Nile.

The lyrics, delivered in aggressive, halting tones reminiscent of American hip-hop, rely heavily on street slang indecipherable to most Egyptians of a certain age or class. And its influence is growing.

What is unusual about mahraganat is that it's a clean break with the past: there is no real kinship between it and the sounds that have come out of Egypt's most densely populated districts for decades. And it offers an excruciatingly honest commentary on the social life of the disfranchised young populations of the country's less visible neighbourhoods.

"Some call it electro shaabi but the correct name is mahraganat," says DJ Sadat. The alternative name refers to shaabi, the "music of the people", a decades-old traditional style from the nation's poorest quarters.

"It's pure energy. We give ourselves to people - body and soul. We dance, we sing, we're entranced on stage. It's engaging. For those who listen to us it's a way to vent the frustrations of everyday life, to forget for a few hours their problems."

Sadat and his friends started playing mahraganat six years ago in their neighbourhood.

"We were the first guys who started to sing, record, mix and upload wedding songs that later became known as mahraganat. The first song was called El Salam Festival. Here, everybody knows us."

Salam City is where Sadat, 26, grew up, where he developed the music and where he produces his own recordings in the home studio of his three-room apartment. He's helped by Alaa 50 Cent and Amr Haha, two neighbourhood friends, and the three of them make music that combines shaabi, hip-hop and electro with lyrics that talk openly about sex, drugs, unemployment and police brutality.

"The secret to our success is that people in their 20s feel represented by our music," Sadat says. "We talk about our common problems: the difficulty of having a relationship with a woman, rising unemployment, and drugs that we do to help us not get depressed."

The group learned how to delegate in order to maximise their reach. While they wrote lyrics, programmed beats and mixed the recordings, they found other tech-savvy partners who knew social media, especially YouTube, to broadcast their performances. Some of the videos posted on YouTube picked up more than a million views, and it's not hard to see their attraction in a conservative country, since sex is one of their main subjects.

"Sex outside of marriage is not accepted," Sadat says. "So you have to get married. But not everyone has the money to start a family. So if you want to have a girlfriend and stay with her, you must do so secretly, stealthily."

Sadat also sings about sexual repression, about girls from "good" families who reject the rough boys from his part of town, and about girls too obsessed with marriage to ever consider a casual relationship. But he rejects the notion that his verses are simplistic or misogynistic.

"We've written songs against sexual harassment, a frequent problem in the country," he says.

He even has a song called I Look but I Don't Grope, with the chorus: "If you are a real man, protect, don't harass."

Then there are drugs - Sadat smokes two joints during our two-hour interview. "I write a lot about hashish. It hurts, I know. But I can't live without it," he says.

In the wake of the resignation of President Hosni Mubarak in February 2011, it didn't take long for Sadat and his friends' music to reach beyond Salam City.

"Usually, young people who are born here don't have much hope for the future," Sadat says. "If you're lucky, you can become a mechanic or a taxi driver. But if it goes wrong, you deal drugs. I'm considered a hero by my peers because I've done it: I succeeded with the music."

Mahraganat quickly spread to similar suburbs, reaching new audiences. And as Egypt changed, so did Sadat's message - the group released a song called Mubarak Bites as Egypt revolted.

After Mubarak's fall, too, there was more opportunity to speak freely. Sadat's songs began tackling politics, a previously dangerous subject. Political killings, military brutality and the Muslim Brotherhood were all pondered in song.

For once, an underground cultural force was in perfect tune with popular sentiment.

"I always listen to it in the car," said a young taxi driver, turning up the volume. "Some of my friends know the lyrics by heart. Not me, though. I don't think they mean anything. I think that people are attracted mainly by the frantic pace.

"Egyptians are like that: they love the excesses in all areas, even in music."

- Observer