The Screen shot below shows the CPU usage of AT2800USB, DVB-T/H Modulator while playing a Transport Stream file from the harddisk.
The PC used was  a Pentium 4,3.0GHz based PC with 1GBytes intern RAM  under Windows XP operating system.

The Screen shot below shows the CPU usage of AT2800USB, DVB-T/H Modulator in the pass through mode.
The Transport Stream for modulation comes from an external source via the DVB-ASI  or DVB-SPI inputs ( in this example from DVB-ASI, Serial ).
As a result the CPU occupancy is zero, all the modulation is done in the hardware leaving the CPU resources to be used for user application software.