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Abstract

The present invention includes a digital stereo modulator having a digital left channel input and a digital right channel input into a Digital BTSC Stereo Generator that contains a Sine Table. The Digital BTSC Stereo Generator generates and outputs the following signals: 2*F.sub.H, compressed BTSC L-R, preemphasized BTSC L+R, and F.sub.H. A digital multiplier amplitude modulates the 2*F.sub.H carrier with the compressed BTSC L-R output, and the resultant signal is a Stereo Subchannel AM-DSB-SC BTSC Compressed L-R, which is then summed together with the preemphasized BTSC L+R, and F.sub.H by a digital summer. The output of the digital summer is the composite BTSC output without SAP or Professional channels. The Digital BTSC Stereo Generator transforms left and right inputs into the outputs described above by utilizing clock inputs 3*F.sub.H and 12*F.sub.H. A digital PLL phase locks 3*F.sub.H and 12*F.sub.H clocks to a Horizontal Synch (F.sub.H) reference, for input to the Digital BTSC Stereo Generator. The 3*F.sub.H clock represents the sample rate of the digital left and right inputs. This sample rate is interpolated, by a factor of 2 to a rate of 6*F.sub.H, in the Digital BTSC Stereo Generator. The sample rate is additionally interpolated to 12*F.sub.H to allow digital representation of the composite BTSC output which has an upper 3 dB frequency component at 46.468 KHz. All clocks in the Digital BTSC Stereo Generator being integer multiples of F.sub.H allows simple and accurate synthesis of the 2*F.sub.H carrier by examining a sine look up table. If the clocks are not integer multiples of F.sub.H, more complex techniques can be utilized to generate F.sub.H and 2*F.sub.H.

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First Claim