Each process has a priority setting that Linux uses to determine how fast it should run relative to the processes on the system. You can set the priority of a process by starting it with the nice command:

$ nice -n 10 oggenc /tmp/song.wav

Because the priority setting is called nice, it should be easy to remember that a higher value will be nice to other processes, allowing them to get priority access to the CPU. By default, processes are started with a setting of 0, so the setting of 10 above means oggenc will readily give up the CPU to other processes. Generally, this means that oggenc will allow other processes to run at their normal speed, regardless of how CPU-hungry oggenc happens to be. You can see these niceness levels under the NI column in the ps and top listings above.