A signal processing device comprising: an extracting unit that extracts a low frequency component of an audio signal, envelope information representing an envelope of a high frequency component of the audio signal, noise envelope information comprising information representing a boundary position of a plurality of zones into which noise signals included in the high frequency component are divided and information representing gain of the noise signals in each zone, and sine wave information which includes information representing a distance in time from a start position of a frame of the high frequency component to an appearance start position of a sine wave component included in the high frequency component, wherein the start position for the sine wave component is independent of the boundary position for the noise signals, and is for specifying a frequency and an appearance position of the sine wave component; a pseudo high frequency generating unit that decodes the envelope information and generates a pseudo high frequency signal configuring the high frequency component on the basis of a low frequency signal, the low frequency signal being the low frequency component; a noise envelope information decoding unit that decodes the noise envelope information and generates a noise signal based on the noise envelope information by adjusting the gain for each zone to match the gain represented by the noise envelope information for that zone; a sine wave generating unit that generates, based on the sine wave information and the decoded envelope information, a sine wave signal which is at a frequency represented by the sine wave information and in which the appearance start position specified from the sine wave information is set as a start position; and a combining unit that combines the low frequency signal, the pseudo high frequency signal, the noise signal, and the sine wave signal to generate an audio signal. an extracting unit that extracts a low frequency component of an audio signal, envelope information representing an envelope of a high frequency component of the audio signal, noise envelope information comprising information representing a boundary position of a plurality of zones into which noise signals included in the high frequency component are divided and information representing gain of the noise signals in each zone, and sine wave information which includes information representing a distance in time from a start position of a frame of the high frequency component to an appearance start position of a sine wave component included in the high frequency component, wherein the start position for the sine wave component is independent of the boundary position for the noise signals, and is for specifying a frequency and an appearance position of the sine wave component; a pseudo high frequency generating unit that decodes the envelope information and generates a pseudo high frequency signal configuring the high frequency component on the basis of a low frequency signal, the low frequency signal being the low frequency component; a noise envelope information decoding unit that decodes the noise envelope information and generates a noise signal based on the noise envelope information by adjusting the gain for each zone to match the gain represented by the noise envelope information for that zone; a sine wave generating unit that generates, based on the sine wave information and the decoded envelope information, a sine wave signal which is at a frequency represented by the sine wave information and in which the appearance start position specified from the sine wave information is set as a start position; and a combining unit that combines the low frequency signal, the pseudo high frequency signal, the noise signal, and the sine wave signal to generate an audio signal.