Magnetic disk apparatus and method

A magnetic disk apparatus comprising:

• a magnetic disk on which multiple servo sectors are provided in a circumferential direction, the multiple servo sectors each storing a first burst pattern and a second burst pattern;
• a magnetic head configured to execute writing and reading on the magnetic disk;
• and
• a controller configured to, upon the magnetic head passes over a first servo sector being one of the multiple servo sectors,
• identify read timing of the first burst pattern and the second burst pattern,
• read, at the read timing, the first burst pattern and the second burst pattern from the first servo sector,
• acquire a first amplitude and a first phase of a first read waveform and a second amplitude and a second phase of a second read waveform by demodulating the first read waveform and the second read waveform, the first read waveform being a read waveform of the first burst pattern, the second read waveform being a read waveform of the second burst pattern,
• acquire weights on the basis of the first amplitude, the second amplitude, the first phase, and the second phase,
• correct an initial phase of each of the first read waveform and the second read waveform on the basis of an initial phase correction value obtained by weighted average calculation using the weights, the first phase, and the second phase, and
• perform positioning of the magnetic head on the basis of the first read waveform and the second read waveform, each of whose initial phase has been corrected.