Random access media (such as hard disks, or USB or flash drives) can produce a true digital copy of your data, because every bit value is maintained. Sequential media (such as digital tape) use error correction schemes to fix the occasional bad data that is received in a digital transfer. These corrections are deviations from the actual data, and with successive reproductions, represent a subtle form of generation loss.

You can avoid this loss by creating and maintaining masters on random-access digital media (such as a hard drive) and transferring them to sequential digital media only as needed.