Compatible four channel recording and reproducing system

Abstract

A compatible four channel sound system for use in conjunction with a recording system for recording four individual audio signals designated L.sub.f, L.sub.b, R.sub.b and R.sub.f on a recording medium having first and second primary information channels and first and second subsidiary information channels, the first and second primary information channels carrying information that is consistent and compatible with existing monophonic and stereophonic standards. In accordance with the preferred embodiment of the invention, means are provided for forming a first composite signal designated L.sub.T which contains, to the extent they are present, L.sub.f in a dominant proportion and L.sub.b and R.sub.b in sub-dominant proportions, L.sub.b and R.sub.b being phase shifted with respect to each other. Means are also provided for forming a second composite signal designated R.sub.T which contains, to the extent they are present, R.sub.f in a dominant proportion and L.sub.b and R.sub.b in sub-dominant proportions, L.sub.b and R.sub.b being phase shifted with respect to each other. Further means are provided for forming a first auxiliary signal by combining all of the individual audio signals, L.sub.f, L.sub.b, R.sub.b and R.sub.f, to the extent they are present, and for forming a second auxiliary signal by combining all of these individual audio signals, L.sub.f, L.sub.b, R.sub.b and R.sub.f, to the extent they are present, the individual audio signals being combined in different relative phase relationships in the first and second auxiliary signals. BACKGROUND OF THE INVENTION This invention relates to audio systems and, in particular, to a sound system adapted to record four or more individual channels of audio information containing directional information on a two track record medium and to reproduce the recorded information as four discrete audio output signals having the directionality of the original input signals. The subject matter of this application is related to subject matter in the co-pending application Ser. No. 462,044 entitled "Compatible Four Channel Radio Broadcast and Receiving System" filed of even date herewith and assigned to the same assignee as the present application. In commercial stereophonic systems, two independent signals respectively modulate the two tracks (left and right walls) of a single groove record in two perpendicular directions. Typically, the groove is cut with modulation in each wall of the groove representing one of the signals and with lateral modulation representing the sum of the signals and vertical modulation representing the difference between the signals. In my U.S. Pat. No. 3,761,628 there is disclosed a sound system wherein four individual audio signals, designated L.sub.f, L.sub.b, R.sub.b and R.sub.f are encoded in accordance with the "SQ" quadraphonic technique to produce two composite signals designated L.sub.T and R.sub.T and are also encoded to produce two additional "conjugate" composite signals which may be designated L.sub.T * and R.sub.T *. The composite signals L.sub.T and R.sub.T can be recorded at baseband frequency on the respective walls of stereophonic disc records and the "conjugate" composite signals L.sub.T * and R.sub.T * can be used to modulate carrier signals which are also recorded on the walls of the record groove. The referenced patent demonstrates that L.sub.T and R.sub.T can be decoded in conventional fashion using an "SQ" decoder matrix to produce four signals designated L.sub.f ', L.sub.b ', R.sub.b ' and R.sub.f ', each of these signals containing, in predominant proportion, a corresponding one of the four individual audio signals, along with certain "unwanted" components in sub-dominant proportions. For reproducing equipment that is capable of obtaining only L.sub.T and R.sub.T, these four signals L.sub.f ', L.sub.b ', R.sub.b ' and R.sub.f ' suffice as satisfactory although not fully "discrete" outputs for audio reproduction. The patent demonstrates that L.sub.T * and R.sub.T *, which can be obtained using more sophisticated reproducing equipment, can also be processed using a "SQ" type of decoder, to produce four signals which may be designated L.sub.f '*, L.sub.b '*, R.sub.b '* and R.sub.f '*, and these latter four signals can be added to L.sub.f ', L.sub.b ', R.sub.b ', and R.sub.f ', respectively to recover the original four individual audio signals in fully discrete form. Thus, by providing the record with appropriate "auxiliary signals" (i.e., L.sub.T * and R.sub.T *), consumers are given a choice as to the level of sophistication and expense of their reproducing equipment. Consumers having equipment with full capability can obtain four fully discrete audio outputs and those having less expensive matrix decoding equipment alone can obtain four conventional "SQ" outputs. Also, since the "SQ" composite signals on the disc basebands are fully compatible with stereophonic and monophonic reproduction, the needs of consumers having only the basic stereo or mono players are satisfied. The sound system of the above-referenced patent is satisfactory, but it is an object of the present invention to provide a compatible four channel system which offers even greater flexibility options to the consumer and also offers certain performance advantages. SUMMARY OF THE INVENTION The present invention is directed to a compatible four channel sound system for use in conjunction with a recording system for recording four individual audio signals designated L.sub.f, L.sub.b, R.sub.b and R.sub.f on a recording medium having first and second primary information channels and first and second subsidiary information channels, the first and second primary information channels carrying information that is consistent and compatible with existing monophonic and stereophonic standards. In accordance with the preferred embodiment of the invention, means are provided for forming a first composite signal designated L.sub.T which contains, to the extent they are present, L.sub.f in a dominant proportion and L.sub.b and R.sub.b in sub-dominant proportions, L.sub.b and R.sub.b being phase shifted with respect to each other. Means are also provided for forming a second composite signal designated R.sub.T which contains, to the extent they are present, R.sub.f in a dominant proportion and L.sub.b and R.sub.b in sub-dominant proportions, L.sub.b and R.sub.b being phase shifted with respect to each other. Further means are provided for forming a first auxiliary signal by combining all of the individual audio signals, L.sub.f, L.sub.b, R.sub.b and R.sub.f, to the extent they are present, and for forming a second auxiliary signal by combining all of these individual audio signals, L.sub.f, L.sub.b, R.sub.b and R.sub.f, to the extent they are present, the individual audio signals being combined in different relative phase relationships in the first and second auxiliary signals. The first and second composite signals are applied to the first and second primary information channels and the first and second auxiliary signals are applied to the first and second subsidiary information channels, respectively. In accordance with the preferred embodiment of the invention, a decoder responsive to the signals carried by the recording medium is provided and includes matrix means for combining the first and second composite signals in predetermined amplitude and phase relationships to obtain four intermediate signals, each of which has a different one of the individual audio signals predominant. The decoder also includes means for combining the first auxiliary signal with each of the intermediate signals to obtain four enhanced intermediate signals each of which has a different one of the individual audio signals predominant. Finally, the decoder includes means for combining the second auxiliary signal with each of the enhanced intermediate signals to recover the four individual audio signals, L.sub.f, L.sub.b, R.sub.b and R.sub.f, in substantially their original form. In the preferred embodiment of the invention the composite signals L.sub.T and R.sub.T are encoded in accordance with the "forward looking" type of "SQ" code. This facilitates the use of auxiliary signals which can be provided at reduced relative amplitudes with respect to the components of the composite signals. Further features and advantages of the invention wll become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.

Dependencies are inferred from the claim text.