At WWDC 2021, Apple announced iOS 15, macOS Monterey, and AirPods upgrades, but it appears that the company decided not to announce certain audio features.

As discovered by reddit user u/hzfan, the current iOS 15 developer beta includes a new "Spatialize Stereo" setting in the Control Center. This replicates the 360-degree acoustics of Apple Music's spatial audio, even if the tracks were not originally mastered for Atmos.

9to5Mac further investigated and found that not only is Spatialize Stereo available in macOS Monterey, but the feature works with both music and video. In the latter case, Apple's 3D head tracking feature is also included. This particular feature requires AirPods Pro or AirPods Max, but again, it apparently works even without Atmos support for video.

The Spatialize Stereo option seems to basically just use up-mixing (a long established technique for extending stereo or mono audio to 5.1 surround sound). However, while this concept is not new, this feature would be a great boost to the way we enjoy music and video on our Macs and iPhones.

The main problem with Apple's spatial audio technology is the relative lack of supported content. For both video and Apple Music content, songs, TV episodes, and movies must be encoded for Atmos. While not particularly uncommon, such encoding is far from the norm: when spatial audio was launched on Apple Music on June 7, only a few thousand of the service's 75 million song library were available in Atmos format. [u/hzfan states that he would "choose Atmos spatial audio mixes over Spatialized Stereo every time. However, if it works well enough, it may be worth using until more content is available with Dolby Mastering.

Perhaps you can try Spatialize Stereo yourself in July, when both iOS 15 and macOS Monterey enter public beta ahead of their full release this fall.