Pro Audio Technology: High Dynamic Range (HDR) Applies to Audio Too
Can you say high dynamic range or HDR when it comes to audio? High-performance audio company Pro Audio Technology (PRO) says yes.
July 24, 2017
Since the 1980s the public’s ear has gradually been conditioned to hear less and less dynamics.
From the onset of the audio production community’s “loudness wars” emphasis to make music louder and more radio friendly, the actual quality of music has deteriorated. Recalibrating the public’s expectations on what good sound quality should be, the public’s current diminished expectations have spilled over into the home theater market.
Affecting the home theater industry’s public perception on what dynamic audio should be has resulted in a market where home theater performance is misunderstood.
Taking on the daunting task of reeducating the public is the Southern California high-performance audio manufacturer Pro Audio Technology.
The challenge Pro Audio Technology (“PRO”) is taking on is actually twofold: reeducating the public on what good home theaters should sound like, and transitioning that understanding to today’s era of object-based surround sound technologies.
Borrowing a term from the video industry, Paul Hales, president, Pro Audio Technology, explains how the term ‘high dynamic range’ applies to audio.
PRO Defines High Dynamic Range (HDR)
Knowing that it could be confusing to use the term high dynamic range to describe audio performance, Hales says that it is nevertheless worthwhile.
Hales says the phrase ‘high dynamic range’ when applied to audio equates to the differences between the highest ‘level’ a system can reproduce, which is loudness in the case of audio, and the lowest ‘level’ a system can reproduce without disappearing into the system or room noise floor. For comparison purposes he says, think of it as the highest levels of brightness and the deepest black levels in video.
Hales stresses that in the commercial audio market dynamic range is a priority for manufacturers. But, he says in the consumer market dynamic range has mostly been ignored.
Underscoring the importance of dynamics in today’s home audio world, Hales says, “surround soundtracks and especially the new ‘immersive audio’ formats make dynamic range a critical performance criteria in consumer surround sound systems now.”
From the installer perspective, the inability of today’s home audio systems to produce dynamics is troubling for a couple of reasons.
“Dealers should be concerned about dynamic range for two reasons: It directly impacts the performance and reliability of the systems they sell,” explains Hales. “Audio systems with restricted dynamic range will struggle to reproduce the entirety of the loudness range captured in modern soundtracks. When this happens two things result—the system will not be able to satisfactorily reproduce quiet signals such as dialog, and the loudest signals such as sound effects simultaneously without sacrificing the quality of at least one of them. Secondly, the speakers run the risk of catastrophic failure by being driven too hard to reach the peaks in the mix.”
To help improve the situation in the home Hales looks at the commercial market and says the commercial audio industry has put standards in place to ensure consistent performance.
Pointing out SMPTE (Society of Motion Picture and Television Engineers) specifications, Hales states the movie industry defined dynamic range criteria many years ago. Hales comments that SMPTE defines the target dynamic range for movie playback as 85dB at an average level at the reference listening position. Peaks in the listening position are defined to be up to 105dB, and this he says is known as ‘reference level’.
“In essence, Reference Level defines at least 20dB dynamic range,” he notes. “It is actually much higher than that since the quietest sounds in the mix will likely be much lower than the ‘average’ level. With today’s mixes, the peaks are often much higher than 105dB when the system is calibrated for playback at reference.”
The Science of HDR
Addressing the topic of dynamics and how it relates to hardware and system design, Hales says there are some specifications in place to help guide dealers find dynamically capable speakers.
“You can determine if a loudspeaker will be able to reproduce the full dynamic content of movie soundtracks. You just need to know the loudspeaker ‘sensitivity’ [how loud the speaker will play at one meter from the speaker with one watt of input power], a loudspeaker’s maximum power handling, and the distance the speaker must ‘throw’ the sound to reach the listener,” he explains.
Maximum output at one meter can be calculated using this formula:
SPLmax, 1m = SPLo+10* LOG (max input power), where SPLo is the sensitivity specification of the speaker.
Hales points out there are some caveats when determining loudspeaker dynamics indicating that some speaker sensitivity specifications are calculated with the figure of 2.83 volts input and not one watt. Hales comments that with speakers rated at impedance levels lower than 8 ohms 2.83 volts represents more than one watt.
More importantly, as a general warning Hales says that not all specifications are the same.
“Many manufacturers take liberties with their specifications of power handling as well,” Hales warns. “Dealers should be diligent with their manufacturer partners to make sure they are getting valid specs. They should use long-term power handling numbers—the AES spec is best—and avoid using any power handling specifications deemed as ‘peak power.’”
Once the maximum SPL at one meter is determined Hales says the maximum SPL at a given distance can be determined with this formula:
SPLdistance = SPLmax, 1m-20*log (distance in meters)
The goal, Hales continues, is to identify speakers that can reach the 105dB target at the listening distance with headroom. Defining headroom, Hales says there should be 3dB of headroom, which means the speaker should actually produce 108dB at the listening distance.
Dynamics also requires proper system design.
Emphasizing that point, Hales says that dynamic range is a function of a system—and not just the loudspeakers.
“The amplifiers must be able to provide enough clean power to reach SPLmax without clipping or distortion. Two to 3dB of headroom is good to have here too,” he notes. “And of course the geometry of the listening room, loudspeaker locations and listening positions directly impact the requirements of the system. The farther away the listeners sit from the speakers, the higher output will be required from both the power amps and loudspeakers themselves.”
Explaining the Value of HDR to Clients
Discussing a highly technical topic like speaker dynamics with non-technical consumers can be difficult.
Hales recommends that it’s best to speak on an “intuitive level” rather than discussing dynamics on a more technical level.
“Most surround sound customers have experienced the real dynamic range of movies from a commercial cinema, a home theater system—or both,” he says. “So the dealer can describe dynamic range as the differences in loudness of say movie dialog and the loudest explosions in the soundtrack. Clients will undoubtedly be able to relate to the vast differences in loudness between the two. High dynamic range is required in order to cleanly reproduce voices at normal speaking levels and the loudest sound effects without running the risk of loudspeaker or ear damage.”
Showing consumers the value and importance of dynamics is also another major challenge that confronts electronics professionals. Hales says the best way for professional installers to demonstrate the differences between a system capable of dynamics and a system that doesn’t offer dynamics is to have both types of systems on display.
Realistically Hales admits that it isn’t always possible to have a non-dynamic system and dynamic system on the same premises, but a well-designed system can convey the visceral connection that dynamics offer without having to employ a non-dynamic system.
“Fortunately, if you can demonstrate an extremely high quality, highly dynamic system, the superiority of it is easily heard in an absolute sense,” he stresses. “We use this technique at our Experience Center outside LA. We start with a very quiet piece of music—male voice and an acoustic guitar, and we move through immersive audio trailers and movie clips and finish with a rock concert at 120dB SPLmax at the listening seat. The rock concert is so visceral and exciting, and the difference in level between it and the male vocal piece is so great that listeners are able to make an absolute determination of the system without a need to compare it to anything.”
Comparing the experience to speed and driving fast, Hales notes a relevant analogy may be driving two fast cars back-to-back. If one car is measurably faster than another car than it becomes blatantly clear that after driving the tangibly faster car that there is no need to drive the other car. The winner can be identified by relying on only the memory of driving the slower car.
Boiling down the topic of dynamics, Hales states it simply comes down to realism. Hales emphasizes that listener engagement and visceral excitement is much higher through wide dynamic range, and it reduces listener fatigue at the same time.
“Dynamically ‘compressed’ systems struggle to make loud transients signals sound real; they lack the visceral energy to excite listeners and typically become distorted and therefore fatiguing to listen to for extended periods of time,” says Hales. “In these systems, when dialog is reproduced at natural ‘dialog’ levels, the sound effects transients are not loud enough to be believable—the dynamic range is compressed. If you turn the system up so the effects are dynamic, dialog is unnaturally loud and you run the risk of blowing up your loudspeakers. You can never achieve both accurate soft and loud sounds from these systems.”
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