As I understand it, the closest thing to the "sounds of slavery" that was still around when the era 
of sound recording would be field calls and songs. That was a musical-oral tradition that was still 
pretty much as it was in the pre-1864 days well into the 20th century. I know Lomax recorded field 
calls and songs, which would be direct descendants of this tradition and may have included snippets 
that can be traced directly back to the slave-era fieldhands.

Now, another thing Lomax recorded, which is still semi-alive today, is this music that's a blend of 
African beats and American fife and drum corps routines. It's considered one root of the blues and 
was covered a bit in the first part of Martin Scorsese's "The Blues" series of films, in the first 
film I believe. Working strictly from memory here, so I might have it only partly right, but I 
believe that music dates from slave days and is a direct link back to West Africa.

Finally, there are still plenty of spirituals sung in black churches today that were sung 

A good place to start would be reading some first-person histories of former slaves. These may be 
found in many places (historical societies, archives, etc) and books. Music was an important part of 
slave culture and is discussed in detail in some of the first-person accounts.

-- Tom Fine