A method for encoding a signal, comprising: performing signal parsing on input signals to obtain low frequency signals and high frequency signals; encoding the low frequency signals; performing a time frequency transformation process on the high frequency signals; performing a classification decision process on the high frequency signals after the time frequency transformation, wherein the type of the high frequency signals is either a transient signal or a non-transient signal; adaptively encoding the high frequency signals according to the result of the classification decision process; and outputting a bitstream including encoded bitstream of the low frequency signals, adaptive encoded bitstream of the high frequency signals, and the result of the classification decision process; characterized in that the adaptively encoding comprises: allocating a currently available bits according to the current frame type of the high frequency signals; and adaptively encoding time envelopes and spectral envelopes of the current frame of the high frequency signals by using the allocated bits, wherein when the type of the high frequency signals is transient signal, a larger number of bits are used for encoding the time envelopes, and when the type of the high frequency signals is non-transient signal, a larger number of bits are used for encoding the spectral envelopes. performing signal parsing on input signals to obtain low frequency signals and high frequency signals; encoding the low frequency signals; performing a time frequency transformation process on the high frequency signals; performing a classification decision process on the high frequency signals after the time frequency transformation, wherein the type of the high frequency signals is either a transient signal or a non-transient signal; adaptively encoding the high frequency signals according to the result of the classification decision process; and outputting a bitstream including encoded bitstream of the low frequency signals, adaptive encoded bitstream of the high frequency signals, and the result of the classification decision process; characterized in that the adaptively encoding comprises: allocating a currently available bits according to the current frame type of the high frequency signals; and adaptively encoding time envelopes and spectral envelopes of the current frame of the high frequency signals by using the allocated bits, wherein when the type of the high frequency signals is transient signal, a larger number of bits are used for encoding the time envelopes, and when the type of the high frequency signals is non-transient signal, a larger number of bits are used for encoding the spectral envelopes. allocating a currently available bits according to the current frame type of the high frequency signals; and adaptively encoding time envelopes and spectral envelopes of the current frame of the high frequency signals by using the allocated bits, wherein when the type of the high frequency signals is transient signal, a larger number of bits are used for encoding the time envelopes, and when the type of the high frequency signals is non-transient signal, a larger number of bits are used for encoding the spectral envelopes.