The sound of gunshots will echo across two Minneapolis neighborhoods -- one south and one north -- this evening as the Minneapolis Police Department tests the city's Shotspotter system, according to a police spokesperson. A total of 25 to 50 shots will be fired.

The tests will help the department fine tune Shotspotter, the city's network of microphones used to pinpoint the location of a person shooting a gun. Some of the microphone towers connect with video cameras as well, allowing police to see the scene of a shooting immediately after a bullet has been fired.

The system is designed to filter out other loud bangs -- fireworks and backfiring vehicles, for example -- to avoid false reports of gunfire. Early in the Shotspotter's existence, fine tuning was required when police discovered that snowplow drivers accidentally set off the microphones when snowplow blades hit manhole covers.

The Shotspotter microphone network and video cameras have helped crack cases, in one instance filming the scene of a homicide in north Minneapolis immediately after a man was shot to death. Video cameras caught two men driving away as their victim lay dying in the street.

Tonight's tests will occur at 7 p.m. in the Folwell neighborhood and at 8:15 p.m. in the Central neighborhood, according to police. Officers will use a bullet-trapping system that allows them to fire real ammunition. Patrol officers and 911 operators have been notified of the planned tests.