1. A noise estimation apparatus comprising: a correlation calculator configured to calculate an absolute correlation value of a spectrum between a plurality of frames in sound information obtained using one or more microphones, the correlation value indicating a degree of correlation of the spectrum between the plurality of frames; a power calculator configured to calculate a sound power of one target frame among the plurality of frames; an update determiner configured to determine a time constant indicating a degree to which the sound information of the target frame is to be reflected in a noise model stored in a storage, and determine whether the noise model is to be updated to an other noise model, based on the sound power of the target frame and the correlation value, set a predetermined value to the time constant when the sound power is equal to or greater than a predetermined threshold value, and set a larger value than the predetermined value to the time constant when the sound power is smaller than the predetermined threshold value; and an updater configured to generate the other noise model based on a determined result by the update determiner, the sound information of the target frame, and the noise model.