Methods and devices for encoding and/or decoding spatial background noise within a multi-channel input signal

A method for encoding a multi-channel input signal which comprises N different channels;

• wherein the input signal comprises a sequence of frames;
• wherein, for a current frame of the sequence of frames, the method comprising:
• determining whether the current frame is an active frame or an inactive frame using a signal and/or a voice activity detector;
• determining a downmix signal based on the multi-channel input signal;
• wherein the downmix signal comprises less than or equal to N channels;
• determining upmixing metadata comprising a set of parameters for generating, based on the downmix signal, a reconstructed multi-channel signal comprising N channels;
• wherein the upmixing metadata is determined in dependance of whether the current frame is an active frame or an inactive frame;
• determining a covariance for the current frame of the multi-channel input signal, by performing temporal smoothing over multiple frames from the sequence of frames, in dependance of whether the current frame is an active frame or an inactive frame;
• determining one or more parameters of the upmixing metadata based on the covariance for the current frame;
• and
• encoding the upmixing metadata-into a bitstream.