Audio decoding apparatus, comprising: an input interface for receiving an encoded audio signal comprising a core encoded signal, core side information and a time-variable high frequency gain information as additional side information; a core decoder for decoding the core encoded signal using the core side information to obtain a decoded core signal, wherein the core decoder is configured to apply a multichannel decoder processing comprising an upmix for generating decoded channels of a multichannel signal as the decoded core signal or to apply a multi-object decoder processing comprising an upmix for generating decoded objects of a multi-object signal as the decoded core signal; and a post-processor for post-processing the decoded core signal comprising: a band extractor for extracting a high frequency band of the decoded core signal and a low frequency band of the decoded core signal; a high band processor for performing a time-variable amplification of the high frequency band in accordance with the time-variable high frequency gain information to obtain a processed high frequency band; and a combiner for combining the processed high frequency band and the low frequency band, wherein the post-processor is configured to apply the post-processing individually on each decoded channel of the multichannel signal or on each decoded object of the multi-object signal using an individual time-variable high frequency gain information for each channel or each object. an input interface for receiving an encoded audio signal comprising a core encoded signal, core side information and a time-variable high frequency gain information as additional side information; a core decoder for decoding the core encoded signal using the core side information to obtain a decoded core signal, wherein the core decoder is configured to apply a multichannel decoder processing comprising an upmix for generating decoded channels of a multichannel signal as the decoded core signal or to apply a multi-object decoder processing comprising an upmix for generating decoded objects of a multi-object signal as the decoded core signal; and a post-processor for post-processing the decoded core signal comprising: a band extractor for extracting a high frequency band of the decoded core signal and a low frequency band of the decoded core signal; a high band processor for performing a time-variable amplification of the high frequency band in accordance with the time-variable high frequency gain information to obtain a processed high frequency band; and a combiner for combining the processed high frequency band and the low frequency band, a band extractor for extracting a high frequency band of the decoded core signal and a low frequency band of the decoded core signal; a high band processor for performing a time-variable amplification of the high frequency band in accordance with the time-variable high frequency gain information to obtain a processed high frequency band; and a combiner for combining the processed high frequency band and the low frequency band, wherein the post-processor is configured to apply the post-processing individually on each decoded channel of the multichannel signal or on each decoded object of the multi-object signal using an individual time-variable high frequency gain information for each channel or each object.