The musicians bridging Sudan's deep divisions
Following the week in which the people of Southern Sudan voted in a referendum which is likely to result in separation from the north, the BBC's Fergus Nicoll meets a group of musicians who despite their differences, believe their music can help connect people and even overcome the obstacles to peace.
Osman al-Hadi Ahmad is a young man with a shy smile and a warm handshake.
He is noticeably the quietest member of a quartet of Southern Sudanese singers who came to the BBC World Service to celebrate the referendum in song.
In fact, because Sudanese living abroad can vote, all four have registered their votes for separation.
But for Osman al-Hadi Ahmad, it was much harder than for his three ethnic Dinka colleagues.
His personal story neatly encapsulates the national dilemma.
Mr al-Hadi Ahmad gets his Muslim name and Arab features from his father in the northern capital Khartoum - but he grew up with his Dinka mother in the south.
"I was unhappy because I had to choose between by dad and my mum," he says.
"I grew up in the south and saw their suffering. That's why I had to vote for separation.
"In the south, they don't have health or education and the government doesn't help them."
So when it came to the crunch, he concludes: "I was upset to have to vote for separation but I didn't have any choice. I will leave my dad and then I will go to the south."
When the quartet begins to perform, the first song is an example of traditional Dinka call-and-response a cappella.
Elizabeth Makongo and Abuk Deng Deng singing out the lead lines, with Ahmad and the tall, swaying figure of Thomas Mawan Muortat echoing the key phrases.
For the Dinka, singing is an important part of social cohesion: Their songs can be assertions of collective identity, hymns of spiritual well-being, boasts of cattle ownership, marriage songs for women - or just ditties for children mucking about.
On this occasion, the Dinka lyrics are scattered with Arabic phrases and the names of independence leaders John Garang, Salva Kiir and the SPLM (Sudan People's Liberation Movement) jump out at me.
They are name-checking the heroes of the struggle - because this is a war song.
"Sometimes you sing it before you go to war, to raise morale," explains Muortat.
"Sometimes you sing it after the victory."
"It reminds people that we've been in a war for a long time," adds Makongo.
When the quartet meets northern musicians Afifi Ahmad and Nadir Ramzi, there are big hugs and loud, slapping handshakes.
Disappointingly, they do not feel ready to perform together, a kind of cross-border collective.
But this is probably appropriate, because the deep cultural gulf between the music of south and north has been exacerbated by politics.
In post-independence Sudan, southerners have rarely been allowed air-time on national TV or radio.
Dinka acappella does not feature on prime-time in the northern capital Khartoum - or did not until the government's belated and- some would say- half-hearted attempt to "make unity attractive".
Despite the huge numbers of displaced southerners, the markets of northern towns resonate not to Dinka, Nuer or Shilluk traditional songs but the jazzy, big-beat numbers of northern stars whose reputations are so entrenched that, like Elvis, one name suffices: Kabli, Wardi and Abd-al-Qadir.
To hear Ahmad and Ramzi perform together is a treat: A distilled, stripped-down acoustic version of the bouncy, bombastic northern sound.
Ahmad on the violin simply soars, effortlessly improvising on top of Ramzi's precisely-picked guitar melodies.
Debating the seemingly inevitable north-south split, they conclude that Sudan's collective cultural identity will be diminished by a vote for separation.
"But," Ahmad insists, "we'll contact them through our music and they'll contact us through theirs."
"We don't need to get back to war. I really worry about what's going to happen but I think the Sudanese people won't go back to war again."
When the quartet return to the microphones, they switch from war-song to a traditional wedding tune.
Ahmad and Muortat retreat to a corner of the studio to watch Makongo and Deng, whose sudden piercing ululations punctuate the steady rhythm of the song.
"I hope to live in peace," says Deng afterwards, "in a country where I can call myself a first-class citizen, not a second-class citizen."
"I'm very happy indeed, because we've been waiting for this day for a long time and, in the name of God, we did it."
Both Sudan and the South are reliant on their oil revenues, which account for 98% of South Sudan's budget. But the two countries cannot agree how to divide the oil wealth of the former united state. Some 75% of the oil lies in the South but all the pipelines run north. It is feared that disputes over oil could lead the two neighbours to return to war.
Although they were united for many years, the two Sudans were always very different. The great divide is visible even from space, as this Nasa satellite image shows. The northern states are a blanket of desert, broken only by the fertile Nile corridor. South Sudan is covered by green swathes of grassland, swamps and tropical forest.
Sudan's arid north is mainly home to Arabic-speaking Muslims. But in South Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own languages and traditional beliefs, alongside Christianity and Islam.
The health inequalities in Sudan are illustrated by infant mortality rates. In South Sudan, one in 10 children die before their first birthday. Whereas in the more developed northern states, such as Gezira and White Nile, half of those children would be expected to survive.
The gulf in water resources between north and south is stark. In Khartoum, River Nile, and Gezira states, two-thirds of people have access to piped drinking water and pit latrines. In the south, boreholes and unprotected wells are the main drinking sources. More than 80% of southerners have no toilet facilities whatsoever.
Throughout the two Sudans, access to primary school education is strongly linked to household earnings. In the poorest parts of the south, less than 1% of children finish primary school. Whereas in the wealthier north, up to 50% of children complete primary level education.
Conflict and poverty are the main causes of food insecurity in both countries. In Sudan, many of the residents of war-affected Darfur and the border states of Blue Nile and South Kordofan, depend on food aid. The UN said about 2.8m people in South Sudan would require food aid in 2013. The northern states tend to be wealthier, more urbanised and less reliant on agriculture.