Coding mode determination method and apparatus, audio encoding method and apparatus, and audio decoding method and apparatus

A method of encoding an audio signal, the method comprising:

• receiving the audio signal;
• obtaining, performed by at least one processor, signal characteristics of a current frame of the audio signal;
• selecting, performed by the at least one processor, a class of the current frame in the audio signal from among a plurality of classes including a music class and a speech class, based on the signal characteristics of the current frame;
• obtaining feature parameters including at least two tonalities and a linear prediction error, the feature parameters being obtained based on a plurality of frames including the current frame;
• generating a plurality of conditions from one or a combination of the obtained feature parameters;
• determining, performed by the at least one processor, whether an error occurs in the selected class of the current frame based on whether at least one of the plurality of conditions is met;
• when the error occurs in the selected class of the current frame, correcting, performed by the at least one processor, the selected class of the current frame;
• encoding, performed by at least one processor, the current frame, based on either the corrected class or the selected class of the current frame;
• and
• generating a bitstream based on the encoded current frame,
• wherein the at least two tonalities are obtained from at least two frequency regions, and
• wherein the correcting comprises:
• when the error occurs in the selected class of the current frame and the selected class of the current frame is the speech class, correcting the selected class of the current frame from the speech class to the music class;
• and
• when the error occurs in the selected class of the current frame and the selected class of the current frame is the music class, correcting the selected class of the current frame from the music class to the speech class.