Several interesting cinema efforts are now taking place within SMPTE in the 25CSS Cinema Sound Systems Technology Committee and the 20F (F is for Film) Study Group for On-Screen Light Measurement, not to mention the 21DC Digital Cinema Technology Committee. This report discusses the direction of 25CSS.
Cinema audio has been getting its day in the sun lately, evident by the formation last year of the 25CSS committee. However, the jury is still out whether 25CSS will produce anything useful. The committee recently posted an update of its work for its quarterly meeting this month, making now a good time to weigh in. SMPTE 25CSS has three study efforts underway: B-Chain Calibration, Pink Noise, and Immersive Audio.
In understanding my commentary, it’s important to note that the cinema standardization effort in SMPTE has taken on very different tone from when it ramped up in 2000. At that time, standards were needed to enable a massive investment in digital cinema equipment on a worldwide scale. With that investment now having largely taken place, there is little appetite in the marketplace for changes that won’t generate a return-on-investment. The impact, and indeed, the success, of new standards are now very dependent on the new economics surrounding cinema. Another way of saying this is that if it’s not broken, then don’t fix it. But SMPTE’s members are largely engineers through and through, and fixing things is in their blood.
The SMPTE study effort in immersive audio has been collecting data from the two primary immersive audio companies, as well as those that seek a path into the game. Anyone familiar with Dolby Atmos and Auro 3D knows that the philosophies behind each format are very different, and while there may be a few speakers whose placement overlap, it would be very difficult, if not simply impossible, for both systems to be installed in a room and actually share speakers. The group has been challenged from its very formation. It cannot pick a winner, as that would lead to legal action from losers. If it recommends a homogenized speaker layout, it risks being ignored by market leaders Dolby and Auro. In my view, all roads for this group spiral downwards.
The pink noise study effort, on the other hand, may appear to be mundane, but has a very important role in the industry. Pink noise is the signal used to equalize and set levels in cinema sound. When multi-channel sound was first popularized by Dolby, there was no need for a standard signal as Dolby took pain to standardize its products, and successful competitors simply followed Dolby’s lead. Digital cinema, however, opened the door to a more diverse set of audio system manufacturers, each having products with its own pink noise generator. For the sake of effective interchange of sound tracks, manufacturers need guidance in designing their pink noise. This study effort is the first step towards generating such guidance. But as straightforward as this may sound, and nine months into the effort, the group has only scratched the surface in understanding its task. At the current pace, it could take 2-3 years for this effort to produce results.
The B-chain calibration study effort is perhaps the most interesting of efforts taking place in 25CSS. Even though somewhat out of its scope, the group has been obsessed with discussing SMPTE ST202, commonly called the “X-Curve” standard. X-curve is the averaged curve one sees on a real-time analyzer when measuring a flat-response cinema system in an auditorium. Those who don’t understand this tend to mistakenly think that X-Curve is a pre-emphasis curve. There have been plenty of times where this misunderstanding appears to infect a fair part of the SMPTE population.
The group recently conducted an impressive survey of cinema operators and technicians to understand how cinemas cope with sound system alignment today. Some interesting facts emerged. First is that approximately a third of responders do not have formal training in sound system alignment. Second is that the vast majority of responders indeed follow the variance prescribed in ST202 and attempt to align systems within +/- 3dB of the ST202 X-curve, as called for by the specification for mid-frequencies. (The allowed variance is wider at the extremes of the spectrum.) A small percentage attempt to align within 1dB, while another small percentage allow the response to fall outside the +/- 3dB window. The caveat in this is that the vast majority of responders were in the US, while complaints of technicians following X-curve within 1db largely come from outside the US.
My analysis of this is that beginners with no formal training or knowledge of ST202 tend to think that X-curve is an equalization curve, choosing to exactly reproduce it on the screen of their measurement tool, unaware that this tight tolerance forces them to correct room acoustics perceived only at the location of the microphone. The result is over-equalization. The study also showed that a majority of users resort to a single microphone when measuring the room, rather than an array of microphones whose response is averaged as called for in ST202. This only exaggerates the problems associated with exact reproduction of the X-curve. If I may speculate, those that allow wider tolerances than 3dB may very well be the more senior techs, who (wisely) tend to employ minimum equalization and rely more upon their ears.
The question for the B-chain Study Group is what will it do with this information? Notably, the analysis above is not that of the study group, which, oddly, was that “there is no consistency in sound measurement.” Frankly, that fact has been evident for over 25 years…one didn’t need to circulate a massive questionnaire to come to that conclusion.
If there is a thread among the 25CSS study groups, it’s that they each suffer from poor leadership. To improve the situation, SMPTE has been searching for a co-chair for the overall 25CSS Technology Committee since its formation. To this effect, SMPTE recruited acoustical consultant Kurt Graffy for the role. Mr. Graffy’s experience in cinema is limited to the design of new construction, far removed from the issues that plague 25CSS. But hopefully his skills in collaboration will provide the guiding nudges that 25CSS has been lacking.