While in the Inland Empire near LA, I caught someone doing some work on the State Department's Diplomatic Security Service (DSS) repeater on 409.5250 MHz, N293. Besides a test tone, they were looping a test audio track of a man and a woman reading sentences that test the readability and the quality of the digital encoding & decoding. You can hear some of the errors that occurred while I was monitoring.
Eventually it sounded like they got the errors to a minimum, at least by listening to the audio tests. This went on over a couple of days this past week.