Signal processing device, signal processing method and program

A signal processing method, comprising acts of:

• acquiring a stereo audio signal representing stereo audio content, the audio signal comprising a first audio signal and a second audio signal;
• acquiring a stereo external signal representing external sound obtained by collecting ambient sound, the stereo external signal comprising a first external signal and a second external signal;
• setting at least an external mode as an operation mode;
• specifying, when the external mode is set, a direction of an emission source of the external sound with respect to a user, based at least in part on the stereo external signal;
• and
• in accordance with the operation mode and the direction of the emission source of the external sound, generating, from the stereo audio signal and from the stereo external signal, an output signal representing stereo audio provided to the user, the stereo output signal comprising a first output signal provided to the user from a first direction and a second output signal provided to the user from a second direction, wherein:
• when the external mode is set and the direction of the emission source of the external sound is specified to correspond with the first direction, the first output signal is generated from at least the stereo external signal, and also, the second output signal is generated from at least the stereo audio signal, and
• when the external mode is set, generating the first output signal from the stereo external signal only, and generating the second output signal by converting the stereo audio signal to a monaural audio signal.

At least one computer readable medium having instructions encoded thereon which, when executed by a computer, cause the computer to function as:

• an audio signal acquisition device to acquire a stereo audio signal representing stereo audio content, the audio signal comprising a first audio signal and a second audio signal;
• an external signal acquisition device to acquire an stereo external signal representing external sound obtained by collecting ambient sound, the stereo external signal comprising a first external signal and a second external signal;
• an output signal generation device to generate, from the stereo audio signal acquired by the audio signal acquisition portion and the stereo external signal acquired by the external signal acquisition portion, a stereo output signal representing stereo audio provided to a user, the stereo output signal comprising a first output signal provided to the user from a first direction and a second output signal provided to the user from a second direction;
• a mode setting device to set, as an operation mode of the output signal generation device, at least an external mode;
• a direction specification device to specify, when the external mode is set, a direction of an emission source of the external sound with respect to the user, based at least in part on the stereo external signal acquired by the external signal acquisition device;
• a fade control device to control an operation to generate the stereo output signal by the output signal generation device in accordance with the operation mode set by the mode setting device and the direction of the emission source of the external sound specified by the direction specification device, wherein when the external mode is set and the direction of the emission source of the external sound is specified to correspond with the first direction, the fade control device causes the output signal generation device to generate the first output signal from at least the stereo external signal, and also to generate the second output signal from at least the stereo audio signal, and
• when the external mode is set, the fade control device causes the output signal generation device to generate the first output signal from the stereo external signal only, and to generate the second output signal by converting the stereo audio signal to a monaural audio signal.