Creo que es el dolby surround aunque no estoy seguro

https://www.lifewire.com/dts-neo-6-1846892

DTS Neo:6 isn't the only audio processing format than can be used to extract a surround sound field from a two channel source, two other audio processing format that will find available on many home theater receivers that have this capability are Dolby Dolby Prologic II and Dolby Pro-Logic IIx

Dolby Prologic II can expand a two-channel source into a 5.1 channel soundfield, and Dolby Prologic IIx, which can expand a two or 5.1 channel source to 7.1 channels channels.

Saludos