Insertion of sound objects into a downmixed audio signal

An insertion unit configured to insert a first audio signal into a bitstream which comprises a downmix signal and associated bitstream metadata;

• wherein the downmix signal and associated bitstream metadata are indicative of an audio program comprising a plurality of spatially diverse audio signals;
• wherein the downmix signal comprises at least one audio channel;
• wherein the bitstream metadata comprises upmix metadata for reproducing the plurality of spatially diverse audio signals from the at least one audio channel;
• wherein the insertion unit is configured to
• mix the first audio signal with the at least one audio channel to generate a modified downmix signal comprising at least one modified audio channel;
• modify the bitstream metadata to generate modified bitstream metadata;
• and
• generate an output bitstream comprising the modified downmix signal and the associated modified bitstream metadata;
• wherein the modified downmix signal and associated modified bitstream metadata are indicative of a modified audio program comprising a plurality of modified spatially diverse audio signals,
• wherein
• the plurality of spatially diverse audio signals comprises a plurality of audio objects;
• the plurality of modified spatially diverse audio signals comprises a plurality of modified audio objects;
• the bitstream metadata comprises object metadata for the plurality of audio objects;
• the object metadata of an audio object is indicative of a position of the audio object within a 3-dimensional reproduction environment;
• the downmix signal and the modified downmix signal are reproducible within a downmix reproduction environment;
• and wherein the insertion unit is configured to
• modify the object metadata to yield modified object metadata of the modified bitstream metadata, such that the modified object metadata of a modified audio object is indicative of a position of the modified audio object within the downmix reproduction environment.