Decoder for a recorder-decoder system

• US 4,706,282 A
• Filed: 12/23/1985
• Issued: 11/10/1987
• Est. Priority Date: 12/23/1985
• Status: Expired due to Fees

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Knowd, Michael J.
• Primary Examiner(s): Cangialosi, Salvatore
• Assistant Examiner(s): Lewis, Aaron J.
• Application Number:
  US06/812,861
• Time in Patent Office: 687 Days
• Field of Search: 360/60, 360/18, 360/22, 360/29, 360/53, 360/32, 360/6, 178/22.08, 380/3, 380/4, 380/49, 380/59
• US Class Current: 713/168
• CPC Class Codes: G11B 20/00086 Circuits for prevention of unauthorised reproduction or copying, e.g. piracy indicating unauthorised use of record carriers in general G11B23/28; scrambling for television signal recording H04N5/913; network architectures or network protocols for network security H04L63/00; cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
• CPC Class Codes: G11B 20/00123 the record carrier being identified by recognising some of its unique characteristics, e.g. a unique defect pattern serving as a physical signature of the record carrier
• CPC Class Codes: G11B 20/10009 Improvement or modification of read or write signals
• CPC Class Codes: G11B 2020/10546 specifically adapted for audio data

Abstract

An improved decoder for a recorder-decoder system wherein a threshold level detector is included in the decoder. The recorder provides for the recording of an audio signal plus a data signal. The data signal includes zero crossing information for sequential increments of time plus an indication of whether the threshold level was met for an increment of the recorded audio. Upon playback the decoder also provides a data signal based on the recorded audio. The threshold level detector of the decoder is higher than that of the recorder. If the recorded data signal indicates the threshold was not met and the same threshold indication is not provided by the threshold level detector of the decorder for the corresponding increment of the recorded audio signal, tampering of such audio increment of the recorded audio is considered to have occurred.

Claims

1. An improved decoder for a recorder-decoder system having a recorder which records an audio input and records a data signal that includes a count of zero crossings of the recorded audio occurring during sequential increments of time with a threshold information bit provided for each count indicating whether a threshold level in the recorder was satisfied by the recorded audio at least once during a count, the decoder for the system providing for playback of the recorded audio and recorded data signal with a count of zero crossings of the recorded audio made during sequential increments of time with the data signal count for an increment of time when the threshold level was indicated as being met being compared with the count obtained by the decoder for the same increment of the recording to provide a measure of whether the recorder audio for such increment was tampered subsequent to its being recorded, the improvement including:

a threshold circuit included in the decoder which is operable during playback of the recorded audio and recorded data signal for detecting whether the recorded audio exceeds the threshold level of said threshold circuit while a zero crossing count of the recorded audio is being made, said threshold level being higher than the threshold level of the recorder whereby an additional check for tampering of the recorded audio is provided in that tampering of the recorded audio is considered to have occurred if the threshold information bit for a count of zero crossings in the recorded data indicates the threshold level was not met and the threshold level indication provided by the threshold circuit of the decoder during the playback of the recorded audio of the corresponding increment of the recorded audio signal indicates the threshold level was met.