Vibration is always critical for Melvin Gibbs, whose electric bass has motored everyone from Ronald Shannon Jackson to Rollins Band. His new EP, 4 + 1 equals 5 for May 25, was made in response to the energies he sensed at a site of pilgrimage — the Minneapolis intersection where George Floyd died under the knee of a police officer, just over a year ago. "Message from the Streets" suggests a suite in miniature: Kokayi's indignant poetic invocation (over a haunting synth drone) leads to Gibbs' electric bass solo (in a plaintive blues mode). The beat arrives — sampled handclaps, then trap rhythm — as Kokayi returns, rapping with grim resolve. A music video shows Gibbs as a visiting griot in George Floyd Square, interspersed with footage from protests and police bodycams. It underscores a point: This music is an attempt to bear witness, and its considerable power comes from the ground up.