Source is the unofficial name of the sound driver used in Commodore 64 games developed by Source, Vektor Grafix and the latter's subsidiary Sprytes Limited. Both companies were based in Leeds, West Yorkshire, England and had Paul Summers use this driver on 5 games. At Source, it superseded Unknown C64 Driver.
The driver was evidently designed with MIDI in mind, as 24h and 28h stand for bass drum and snare drum. Later versions resemble the driver in Motor City Patrol (NES).
Desolator (C64) uses drum samples, and Carrier Command (C64) has leftovers of the sample driver.