This paper describes a new coding method based on binary <inline-formula> <tex-math notation="LaTeX">$(d,k)$ </tex-math></inline-formula> runlength constraints used for recording or transmitting an audio or video signal, computer data, etc. Data words of <inline-formula> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> bits are translated into codewords of <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> bits using a conversion table. The codewords satisfy a <inline-formula> <tex-math notation="LaTeX">$(d,k)$ </tex-math></inline-formula> runlength constraint in which at least <inline-formula> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> and not more than <inline-formula> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> ‘0’s occur between consecutive ‘1’s. The <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>-bit codewords alternate with <inline-formula> <tex-math notation="LaTeX">$p$ </tex-math></inline-formula>-bit merging words which in the prior art are selected such that the <inline-formula> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> are satisfied at the borders of consecutive codewords. We present a new coding method, where the codewords obey the <inline-formula> <tex-math notation="LaTeX">$(d,k)$ </tex-math></inline-formula>-constraint, but the merging words are not required to obey the <inline-formula> <tex-math notation="LaTeX">$(d)$ </tex-math></inline-formula>-constraint. The merging word that satisfies said conditions, yielding the lowest low-frequency spectral content of the encoded signal obtained after modulo-2 integration, is selected. The spectral performance of the new coding method has been appraised by computer simulations for the EFM (Eight-to-Fourteen Modulation) parameters, <inline-formula> <tex-math notation="LaTeX">$d=2, k=10$ </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">$p=3$ </tex-math></inline-formula>. The low-frequency content of the signal generated by the newly presented coding method is around 4 dB lower in the relevant low-frequency range than that generated by the conventional EFM method.
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