Glen Burnie: On a sweltering Sunday morning in a little church not far from Washington, DC, a mesmerising singing rises and falls, rises and falls, over and again - each peak higher than the previous - before the band reaches a joyous clapping, foot-stamping crescendo an hour after their quiet start.
This is one of the last of the Singing and Praying Bands, one of the great and almost unknown American sacred music traditions.
As recently as the 1950s there were thousands of members of Singing and Praying Bands linked to Methodist churches around Chesapeake Bay in the states of Maryland and Delaware.
Their roots - and their music - stretch back in time and place across the American South to West Africa.
Slave masters often frowned on religious gatherings of their human property, explains Clifford Murphy, who is working to document the tradition for the Maryland State Arts Council. Sedition could grow in unsupervised gatherings.
So the slaves took their worship underground into what were known as "brush arbours". In those secret services, Christian worship melded with older musical traditions.
After the Civil War the music and prayer of the brush arbours resurfaced in Methodist churches, especially just north of what had been the border states on the Atlantic coast. The Singing and Praying Bands were born.
After the regular Sunday service on May 17 concluded at the Hall United Methodist Church, the band members - around 15 men and women - come forward.
A line of chairs is placed between the altar and the pews - this is known as the mourning bench - and the men stand on the altar side of the bench facing the women, whose backs are to the congregation.
They wear smocks and aprons, reflecting their slave heritage. They are all in white, though in winter they will add black.
In a capella they begin the first hymn, Take the Name of Jesus with You.
The uninitiated would struggle to understand any of the words but those of the hymn leader, who proclaims the first line of each verse. When the band responds with the rest of the verse the words are so stylised as to be indistinct.
If you strain you can hear aural flashes of gospel and blues and even spiritual chanting. When during the later verses of each hymn the singers start whooping and clapping in euphoria, you get a sense of jazz - though Dr Murphy will later remind me that this music pre-dates jazz and blues and even gospel.
Asked if this music is unique, he says he normally avoids using that word to describe any musical tradition. In this case, he says, he'd make an exception.
A hymn that a traditional Methodist church might knock off in two or three jaunty minutes takes a Singing and Praying Band about 10 minutes from its gentle start through the crescendo.
At first it sounds as though the band is singing in concert, but soon you realise it is in fact more complex - many of the singers begin each word slightly apart from the others. Listen closely and you can pick up and follow a single voice for minutes before being captured by another.
As the hymn ends, the band kneels at the mourning bench for prayers, each led by a different member.
One prayer is offered for a great-grandfather who saw a grandchild's blue shirt, his first colour in years. Another that those on the streets of nearby Baltimore are kept safe.
Another hymn begins - Thou My Everlasting Portion - and the cycle resumes, entrancing both the band and those congregants who have stayed on to watch their worship.
Recently awareness of the Singing and Praying Bands has spread, with state and federal arts bodies beginning to pay attention, leading to a performance at the Kennedy Center in 2014.
Dr Murphy attributes this re-awakening to the folklorist Jonathan David, who was conducting fieldwork in the region back in the 1980s when he met a waterman, as the crabbers on the Chesapeake are known, called Baby Jack Lynch while working on the water.
Lynch referred him to a nearby church.
"You'll hear these people come and sing this really old-time type of singing. And the melodies are so slow and strange that you won't understand a word they say," David recalls him saying.
The meeting changed David's professional life and the book he later wrote, Together Let Us Sweetly Live, has preserved much of the history and tradition of the Bands.
When the Singing and Praying service finally comes to a close and its leader, 64-year-old Reverend Jerry Colbert, sits to talk, he is drenched with sweat but his wind is good and his mood high.
Reverend Colbert's great-grandfather, a slave, was in a Band, though Reverend Colbert was three when he died and does not remember him.
But as with all the other members Fairfax Media spoke to that morning - none of whom were younger than 60 - the Singing and Praying Bands were a constant in his young life through grandparents and parents.
Norris McDonald, also 64, tells of how he remembers the Bands being central to the annual spiritual camps held by the region's churches each summer.
Back then the fields would empty and family members would return home from the city jobs to gather and pray over two weeks, each service accompanied by the Bands.
On the last Sunday the Bands would gather in the evening and sing until a horn was blown near dawn. By then, he says, his mother looked spent, but also, he adds, "as though she was just about to get started again".
Asked if he is worried the Bands might not survive, Dr Murphy laughs and says: "I'm a folklorist - it is my job to worry that they won't survive."
But he observes that unlike many fragile traditions, the Bands are still vital. And most crucially they have not lost their original function. They are not being preserved by custodians concerned for heritage, rather they remain a part of spiritual and community life in the Chesapeake tidewater region.
Reverend Colbert has a simpler take when I put the question to him.
He smiles, mops his brow with the white handkerchief he has just unknotted from his neck and says: "God will send us the voices."
