Modulator circuit for a recording for a digital recording medium

A modulator circuit wherein each input m-bit code is modulated into an n-channel bit pattern, n being greater than m, and two adjacent ones of such n-channel bit patterns are coupled to each other using one of a plurality of margin bit patterns to limit the longest and shortest recording wavelengths while suppressing low band components of a recording waveform, comprising:

• a first logic circuit for adding an n-bit false frame synchronizing signal having a bit pattern at least part of which is the same as part of a frame synchronizing signal in order to achieve unified judgment of at least one inhibited margin bit pattern out of said plurality of margin bit patterns;
• a second logic circuit for referring to the second last, the last and present n-channel bit patterns and the last margin bit pattern to judge at least one inhibited margin bit pattern in accordance with a predetermined algorithm and outputting an inhibition signal representative of the thus judged margin bit pattern out of said plurality of margin bit patterns;
• a digital sum variation measuring circuit for receiving an the inhibition signal, measuring a digital sum variation of each margin bit pattern and an n-channel bit pattern following the margin bit pattern and generating an output signal;
• an integrating circuit for receiving the output signal of said digital sum variation measuring circuit, integrating the digital sum variation with a finite dc gain to generate a controlling signal regarding a cumulative digital sum variation;
• and
• margin bit generating means for receiving the controlling signal regarding a cumulative digital sum variation, a controlling signal regarding a last recording waveform level of an n-channel bit pattern placed prior to the margin bit pattern, and a controlling signal regarding another cumulative digital sum variation of another n-channel bit pattern placed subsequent to the margin bit pattern and outputting from a logic circuit an optimum margin bit pattern from among said margin bit patterns.