All this week, BBC World Service's The World Today programme is looking at cover versions - songs re-recorded by another artist - to find what makes a great cover, and why.
Salman Ahmad is the leader of Junoon, Asia's most popular group. The band's song No More, released after the 11 September terrorist attacks, is based on the poem Pulverised by Polar Levine. Here, Ahmad describes his feelings about the attacks, while below Levine outlines the meaning of his work.
On the morning of 11 September I flew into Karachi, and I went over to a friend's place. It was six o'clock in the evening, and everyone was transfixed.
Jaws dropped, looking at the TV screens. The first plane had just gone into the twin tower.
In a sense, as those planes flew into the Twin Towers, my two worlds of Karachi and New York collided into each other.
I didn't know what to make of it. Like everybody else, I was just trying to make sense of it.
I had a very visceral response to that poem, because the tragedy had not been so graphically put.
It sucked me in.
The thing was, I didn't want to be so sucked into it that I couldn't do justice to what it was.
So I had to go away from it. Then I could see the perspective from a Pakistani Muslim's point of view.
When you're under the microscope, you're being targeted as the enemy. In the following months, we had this huge face-off with India.
We had a million people staring eyeball to eyeball over the borders. We had two nuclear-charged nations.
Then we had the suicide attacks in Karachi, then we had the Daniel Pearl thing in my backyard.
I started thinking, "how do I connect this thing, Karachi and New York?"
I heard the sound of the plane and the crash, and I thought I was dreaming something.
Then I heard sirens, turned on the TV, and there's this building, in my neighbourhood, burning away.
It was my neighbourhood that got attacked, it wasn't just my country. The World Trade Center is right across the street from where my kid plays soccer.
I lived a few blocks north of the thing, and for weeks there was dust everywhere.
It was piled on the street. It was on my window sill and on my floor. You had to clean this dust from all over the place.
I was listening to a broadcast and they were saying what all this dust was - a combination of concrete, pulverised wall board, the plastic from computers, chairs, and the bones of the people who were in the towers.
Suddenly it occurred to me that I'm breathing all these people.
All these people that are missing, that they're digging under the rubble to find - they're all in my lungs.
This is New York - you have a little of everybody on the planet in New York.
I was breathing in Muslims and Jews, Christians and atheists, conservatives and liberals.
I was numb with this notion that I'm breathing in these people, and that's basically what the poem says.
With Junoon, you had this New York Jewish guy who was collaberating on a piece of work about an extraordinary event with a Muslim in Pakistan.
And Pakistan was sponsoring the Taleban, which was the training ground for these folks.
And yet Salman and I became very good friends as a result of this whole thing.
I guess you could say it's the mirror image of the destruction.
The World Today programme would like your comments, to be broadcast on air. If you would like to comment on this story, please use the form on the right.