A NEW APPROACH
The use of digital signal processing to create virtual surround sound is not new. It has been around for decades. Dolby Headphone is an example of such technology. Although it uses the principle of HRTF to generate positional audio cues from two-channel audio mixes, it didn’t sound good to most people because, as I mentioned earlier, everyone has a diﬀerent HRTF and a single fixed digital signal processing profile isn’t going to be good enough. However, new methods and technologies are being developed to maximize the potential of digital signal processing.
Smyth Research was probably one of the first to put out a system that could realistically render the sound of listening to speakers in a room through headphones by using custom HRTFs. Released around eight years ago, it was called the Realiser A8 and it features what Smyth Research calls this the Smyth Virtual Surround (SVS) technology. Its standout feature was that it could measure and create custom HRTF profiles of its user and then use digital signal processing to create the ideal target response so that headphones would sound like speakers in a room.
Included with the Realiser A8 are measurement microphones that are able to capture the unique profile of each user’s head and ears. The only problem lies in capturing the HRTF of the user properly. To do so required a speaker setup and an ideal listening room, which is terribly ironic if you think about it. However, if you have all the ingredients in place, audio journalists and reviewers claimed that listening with headphones through the Realiser A8 was almost as good as listening to a set of good speakers in a room. In his report, long- time audio journalist Steve Guttenberg said that “The Realiser A8’s spatial localization is 100% convincing.”
Recently, Creative came up with a more practical solution. Dubbed Super X-Fi, it made its debut at the Consumer Electronics Show 2018 earlier this year. Born from 20 years of research in room acoustics, human anthropometry, headphones, and music, it uses the same principle as Smyth Research’s Realiser A8, but with a twist. Realizing that it would be almost impossible for users to create their own personalized HRTFs with measurement microphones, a loudspeaker setup, and a listening room, Creative did the next best thing, which is to approximate users’ HRTFs using AI.
Creative simplified the profile creation process by developing an app that would measure and take the key readings of a listener’s heads and ears. This app would then take these measurements and cross-reference it against Creative’s large database of ears and heads measurements and profiles that they have created whilst they were developing Super X-Fi. While they admit that this won’t be as accurate and precise as measuring in a proper listening room, this is infinitely more convenient. Once the profile is created by the app, it can be loaded into the SXFI amp, a small portable USB amplifier and DAC and users can enjoy surround sound wherever they go.
Everyone has a different HRTF and it can vary wildly. These variations explain why it is possible for individuals to arrive at differing conclusions of a headphone.