1. A signal processing apparatus that upconverts a plurality of content data, comprising: an operation unit configured to receive an operation instruction from a user; a generating unit configured to generate user's preference information based on an operation history corresponding to the operation instruction; a processing unit configured to upconvert the plurality of content data; and a control unit configured to calculate a preference level of each content data based on the user's preference information and content information about each content data and to preferentially upconvert content data having a high preference level; and a calculating unit configured to calculate an estimated processing time necessary to upconvert each of the plurality of content data, wherein the control unit preferentially upconverts content data having a shortest estimated processing time.