A product of reduced sulfur content is produced from an olefin-containing hydrocarbon feedstock which includes sulfur-containing impurities. In speech coding method according to a code-excited linear prediction speech coding, a noise level of a speech in a concerning coding period is evaluated by using a code or coding result of at least one of spectrum information, power information, and pitch information, and various excitation codebooks are used based on an evaluation result. If the vehicle is an automobile and the interior space is the passenger compartment therein, the first substructure can be the passenger seat and the second substructure can be the A-pillar, in which case, the processor determines the presence or absence of a passenger in the passenger seat.