What kind of upsampling does the Source D/A utilize?

The Source D/A’s are 8x upsampling when playing at a 44.1kHz rate, 4x at 88.2 and 2x at 192. They run at either 352.8kHz (44.1, 88.2, 176.4) or 384kHz (48, 96, 192). The decoder detects the frequency and selects the upsampling mode automatically.