1. A signal classification method in an encoding device, the signal classification method comprising: classifying, performed by at least one processor, a current frame as one from among a plurality of classes including a speech class and a music class, based on a first plurality of signal characteristics; generating a plurality of conditions, based on one or more of a second plurality of signal characteristics obtained from a plurality of frames including the current frame; first comparing one of the plurality of conditions with a first threshold value and second comparing a hangover parameter with a second threshold value; and correcting a classification result of the current frame, based on a result of the first comparing and second comparing, wherein the second plurality of signal characteristics includes tonalities in a plurality of frequency regions, a long term tonality in a low band, a difference between the tonalities in the plurality of frequency regions, a linear prediction error, and a difference between a scaled voicing feature and a scaled correlation map feature.