For all the debate over surround for HD radio, and radio in general, we may be losing sight of what we are trying to accomplish here.
From the broadcasters’ point of view, we are trying to bring some excitement back to a medium that hasn’t really had any innovation since FM stereo in the early 1960s. But ultimately we are in the business of entertaining people – real people, in real environments who listen to all of their speakers at once. People who have started to appreciate surround in the home, but have been stuck for the past 30 years listening to dual stereo in their cars.
So what does it take to entertain? Well, I don’t think separation is the answer. From an engineering point of view, it is all very simple to believe that 5.1 truly discrete channels (or more) is the ideal. Unfortunately, people don’t experience auditory reality through 5.1 (or 6.1 or 10.2) speakers arrayed around their heads.
Our current discrete surround systems simply provide a rather poor simulation of reality by surrounding people with boxes. It might be fun to hear something coming from the rear speakers, but you are always aware that the sound is coming from a box. This situation, and the fact that the playback environment is quite different from the performance or mixing environment, makes any concept of absolute “audio integrity” somewhat suspect.
The true goal of any entertainment experience is to create emotional involvement. It doesn’t take surround to do this; some works are so powerful that listening to them on an acoustic phonograph can move people. But surround can help, especially if the surround system can convince the listener that he or she is truly immersed in the acoustic environment of the original performance.
To me, the real goal of an audio reproduction system is to bring the listener as close as possible to, or beyond, the emotional intensity of a live performance. Whatever system can achieve this goal – discrete, matrix or spatial coding – can be deemed successful, technical differences notwithstanding.
Back to surround radio: What is the value proposition? For the broadcaster it is largely marketing. Surround brings radio on a par with what more and more consumers are expecting from their media sources, since DVDs are now virtually ubiquitous and surround can be heard in every movie theater in major markets.
Interestingly, because DVD-A and SACD are pretty much non-starters, surround radio has a window of opportunity to become the major source of surround-encoded content to the automotive listener. This content need not be limited to pre-recorded material. With radio, original and live productions can be brought to the listener in surround, as is commonly done with Circle Surround encoding in Japan.
For the CE manufacturer, especially in the automotive market, surround provides a way to distinguish their product from the competition and to provide a new and exciting feature for the consumer. But the range of surround material appropriate to the car is limited.
In addition, consumers generally already have large existing libraries of stereo material, either on CDs or most recently on their digital audio players. This makes blind up-mixing an absolutely critical feature. Without this, surround has limited value in the car.
In the automotive environment, post processing can create an exciting immersive auditory experience by compensating for inherent limitations on speaker and listener placement, and by taking full advantage of the resources, such as deck-mounted rear speakers, that are available. In the home, post processing can enhance the perception of dialog and improve the perceived bass performance of the system, all in the name of providing a more exciting entertainment experience. These types of post processing features add significantly to the value proposition for the CE manufacturer and can propel the adoption of technologies that incorporate them.
So is there consensus on a surround approach anywhere? Recently, in SRS discussions with major automotive and head unit manufacturers, one seems to be emerging. Based on value, simplicity and functionality, these groups are clearly saying that, for the car, for the foreseeable future, they are planning to implement matrix surround systems.
This has been demonstrated by recent Circle Surround implementations by Panasonic, Kenwood, Fujitsu Ten, Eclipse, Toyota and Honda with more to come. Dolby and Harman-based matrix surround systems are also available on a number of platforms.
So it seems the CE and automotive markets have made their decision. The decoders that will be in the hands of the consumer will be matrix-based, at least for the next few years.
That does not preclude the introduction of other surround encode/decode systems in the future, especially since accommodations are being made in the HD Radio bit stream to identify the surround format. This problem was solved long ago in A/V receivers.
The digital bit stream is decoded by the receiver DSP to determine the appropriate decoder to use, be it Dolby Digital, DTS or a matrix decoder or straight Pulse Code Modulation, which is standard uncompressed, unencoded stereo or Lt/Rt (matrix surround encoded) digital audio.
There is no reason this approach could not be applied to and improved upon by HD Radio.
So at least for now, if you want a straightforward surround encoding system that can fit easily into the production workflow, and you want the highest probability of your listeners hearing a surround broadcast in surround, a matrix-based encoding system provides excellent marketing and technical value for today’s market.