Prior art

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US patent 8646001, titled "Signal processing apparatus and methods," has several prior art documents cited. The patent itself mentions several prior art limitations in its detailed description. The most relevant prior art documents cited in US8646001B1 are:

1. U.S. Pat. No. 4,694,490 to Harvey et al.

• Full Citation: US4694490A
• Publication/Filing Date: Priority date: 1981-11-03 (This patent claims priority from US06/317,510, filed on 1981-11-03).
• Brief Description: While the full description isn't available in the provided text, US8646001B1 itself claims priority from this patent (US4694490A), implying a strong relationship. It is likely that US4694490A describes an earlier iteration or foundational aspects of the signal processing apparatus and methods. The current patent builds upon it.
• Potentially Anticipating Claims (35 U.S.C. § 102): Given that US8646001B1 claims priority from US4694490A, the earlier patent could potentially anticipate many or all claims of US8646001B1, depending on the specific differences and new inventive steps introduced in 8646001. A detailed claim comparison would be necessary to determine exact anticipation.

2. U.S. Pat. No. 4,381,522 to Lambert

• Full Citation: US4381522A
• Publication/Filing Date: Not explicitly stated, but the patent states it "describes a cable television system controlled by a minicomputer that responds to signals transmitted from viewers by telephone."
• Brief Description: Describes a cable television system where a minicomputer responds to viewer signals transmitted by telephone. The computer generates a schedule of prerecorded local origination programs based on viewer input, creates a video image of this schedule, transmits it over a cable channel, and then actuates video players to transmit the requested programming.
• Potentially Anticipating Claims (35 U.S.C. § 102): This patent anticipates systems for user-requested content and scheduling in a television context. Claims in US8646001B1 related to interactive programming selection, content scheduling, and remote control of content delivery (e.g., in systems involving user input for program selection) might be impacted. The current patent distinguishes itself by stating this prior art "has no capacity to schedule automatically or transmit any programming other than that loaded immediately at the play heads of the controlled video players. It has no capacity to load the video players or identify what programming is loaded on the players or verify that scheduled programs are played correctly. It has no capacity to cause the video players to record programming from any source. It has no capacity to receive programming transmissions or process received transmissions in any way. It has no capacity to operate under the control of instructions transmitted by broadcasters. It has no capacity to insert signals that convey information to or control, in any way, the automatic operation of ultimate receiver station apparatus other than television receivers."

3. U.S. Pat. No. 4,337,480 to Bourassin et al.

• Full Citation: US4337480A
• Publication/Filing Date: Not explicitly stated, but the patent states it "describes a dynamic interconnection system for connecting at least one television receiver to a plurality of television peripheral units."
• Brief Description: Describes a dynamic interconnection system that allows a viewer to automatically connect and disconnect television peripheral units without manual switching or re-cabling. It also allows for "image-within-image" superimposition of a secondary image from a second peripheral unit onto the primary image on the television display.
• Potentially Anticipating Claims (35 U.S.C. § 102): This patent anticipates systems related to connecting and controlling multiple peripheral units with a television, and the display of combined visual information (e.g., overlaying images). Claims in US8646001B1 related to controlling multiple apparatus at a subscriber station or combining media for display could be challenged.

4. U.S. Pat. No. 4,264,925 to Freeman et al.

• Full Citation: US4264925A
• Publication/Filing Date: Not explicitly stated, but the patent states it "describes a multi-channel programming transmission system wherein subscribers may select manually among related programming alternatives transmitted simultaneously on separate channels."
• Brief Description: Describes a multi-channel programming transmission system where subscribers can manually select among simultaneously transmitted programming alternatives on separate channels.
• Potentially Anticipating Claims (35 U.S.C. § 102): This patent anticipates multi-channel transmission and manual channel selection. Claims in US8646001B1 related to providing multiple channels of programming and allowing subscriber selection might be anticipated. However, US8646001B1 distinguishes itself by stating this prior art "has no capacity for interconnecting or operating a system at any time other than the time when the order to do so is entered manually at the system or remote keyboard. It has no capacity for acting on instructions transmitted by broadcasters to interconnect, actuate or tune systems peripheral to a television receiver or to actuate a television receiver or automatically change channels received by a receiver. It has no capacity for coordinating the programming content transmitted by any given peripheral system with any other programming transmitted to a television receiver. It has no capacity for controlling two separate systems such as, for example, an automatic radio and television stereo simulcast. It has no capacity for selectively connecting radio receivers to radio peripherals such as computers or printers or speakers or for connecting computers to computer peripherals (except perhaps a television set)."

5. U.S. Pat. No. 4,025,851 to Haselwood et al.

• Full Citation: US4025851A
• Publication/Filing Date: Not explicitly stated, but the patent states it "describes a system that monitors by means of embedded digital signals".
• Brief Description: Describes a system for monitoring programming by means of embedded digital signals.
• Potentially Anticipating Claims (35 U.S.C. § 102): This patent anticipates the use of embedded digital signals for monitoring programming. Claims in US8646001B1 related to embedding signals in programming for identification and monitoring purposes could be impacted.

6. U.S. Pat. No. 3,845,391 to Crosby

• Full Citation: US3845391A
• Publication/Filing Date: Not explicitly stated, but the patent states it "monitors by means of audio codes that are only 'substantially inaudible'".
• Brief Description: Describes a system for monitoring programming using audio codes that are "substantially inaudible."
• Potentially Anticipating Claims (35 U.S.C. § 102): This patent anticipates monitoring programming using inaudible audio signals. Claims in US8646001B1 related to embedding signals in audio portions of transmissions, particularly those that are not normally audible, could be impacted.

7. U.S. Pat. No. 4,547,804 to Greenberg

• Full Citation: US4547804A
• Publication/Filing Date: Not explicitly stated, but the patent states it "automatically monitors a plurality of channels by switching sequentially among them and that includes capacity to monitor audio and visual quality".
• Brief Description: Describes a system that automatically monitors a plurality of channels by sequentially switching among them and includes the capacity to monitor audio and visual quality.
• Potentially Anticipating Claims (35 U.S.C. § 102): This patent anticipates systems for monitoring multiple channels and assessing audio/visual quality. Claims in US8646001B1 related to scanning multiple frequencies/channels and monitoring programming availability and quality could be impacted. The current patent states that this prior art "has capacity to monitor only single broadcast stations, channels or units and lacks capacity to monitor more than one channel at a time or to monitor the combining of media. At any given monitor station, it has had capacity to monitor either what is transmitted over one or more channels or what is received on one or more receivers but not both. It has assumed monitored signals of particular format in particular transmission locations and has lacked capacity to vary formats or locations or to distinguish and act on the absence of signals or to interpret and process in any fashion signals that appear in monitored locations that are not monitored signals. It has lacked capacity to identify encrypted signals then decrypt them. It has lacked capacity to record and also transfer information to a remote geographic location simultaneously."