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Apparently it is not necessary to deliver sounds to the ears that are identical to the “real thing” for listeners to think that they are hearing something resembling, even closely resem- bling, the real thing. If the basic clues are there, the brain can fill in a lot of blanks. The boundary between reality and per- ception is a blurry one. Perhaps the most perfect sound repro- duction systems are those that provide the most, and the most persuasive, perceptual “hooks” without exhibiting flaws that go beyond the limits of human adaptation.
But expectation also plays into this. There are examples of people hearing things that simply cannot be there. In high-end audio there have been numerous examples of tweaks and gadgets that defy both common sense and physical laws, all of which found a following. If you believe something, there is a chance that you will hear it. All of this can be entertaining so long as it does not encroach on the basics of a family budget.
And then there is the scientific approach.
The literature on concert hall and large-space acoustics and psychoacoustics is extensive, and it has contributed much to understanding sound reproduction in small rooms (Toole, 2006, and 2008, Chapters 4 – 11). However, recording control rooms, mastering rooms, domestic homes and cars are all small spaces. They are subject to enormous variations due to room modes that add low-frequency coloration, and the asso- ciated standing waves dictating that no two people in a room will hear exactly the same bass. At higher frequencies, the small dimensions would seem to be contrary to attempts at creating impressions of being in large spaces. But these are understandable phenomena, responsive to mathematical analysis and psychoacoustic experimentation. The problem is that relatively little scientific effort has been invested in trying to understand the acoustical factors underlying the recorded music and film industries. Is this scientific elitism? As a result, folklore, misinformation and simple ignorance compromise what is achieved in these industries. Without some trustwor- thy technical and acoustical guidance, the circle of confusion will never be broken. At some time, measurements of the right kind need to be trusted to describe what could be considered to be a “reference” sound quality, one that could be the target performance for both production and reproduction. The ques- tion is: what are those measurements?
Identifying the right quantitative measures
The familiar claim that “we cannot measure what we hear” stems from observations that curves may look the same but the sound is different. In the early years of audio this was certainly true. In 2013 it mostly relates to situations where the measured data are inadequate in quantity and quality, or are of the wrong kind, or that post processing has not been applied for more effective interpretation.
An omnidirectional microphone at head height at listen- ing locations has long been employed as a basic method of evaluating sound systems in rooms. Traditionally these have been 1/3-octave filtered steady-state amplitude responses. There is a superficial logic to this, but it is not reasonable to assume that a simple omnidirectional microphone, however technically excellent, coupled to a real-time or other analyz-
consumer playback devices, I will assert that the only consis- tent factors identifying small and/or inexpensive loudspeak- ers are a lack of low bass and an inability to play loud.
So, in our everyday music listening—sound reproduc- tion—what can we expect? At the beginning of the process, microphones sampled the sound field radiating from voices and instruments. All of the sound that would reach our ears in a live performance is not captured. Therefore a perfect reproduction of a “live” event is precluded at the outset.
Storage and playback through two channels has been the industry norm for decades, and it may be convenient, but it is incapable of delivering the timbral nuances, directional effects and spatial envelopment of live performances. Instead we get two “real” sources of sound, the left and right loud- speakers, and some number of panned phantom images between the loudspeakers, assuming that we have the disci- pline to sit in the symmetrical sweet spot. The phantom images suffer from acoustic crosstalk—the sound from both loudspeakers reaches both ears—and both the timbre and spatial representations are unnatural (Toole, 2008, Figure 8.4 and Section 9.1.3). The spectral corruption of the important phantom center image—often the featured artist—is such that even speech intelligibility is degraded (Shirley et al., 2007). With the best of intentions, and unlimited financial investment, when listening to stereo recordings what we hear cannot be the same as a live acoustical experience.
Playing stereo recordings through headphones generates a totally different experience, and one not anticipated by a production process using loudspeakers. It is what it is, and whatever it is, it is not what was intended by the creators of the art. Multichannel audio moves us significantly closer to a desirable objective, but sadly, other than for movies, it has not been commercially viable.
Therefore, in sound reproduction, just as in concert hall situations, the “music” may be relatively constant, but our auditory experiences are not. It is what it is at the time, but because it is reproduced sound, we can play recordings again, and again. However, only if our personal playback equipment shares important qualities with that used to create the art, can we be assured of who or what takes the credit or blame for what we hear. We need to disrupt the “circle of confusion” by making the two domains shown on the right in Fig. 1 as sim- ilar as possible.
How is it that we find ourselves deriving pleasure from this grossly flawed system? It is because human listeners are remarkably adaptable, and not a little bit susceptible. Over 100 years ago Edison, in his “tone tests,” was able to persuade nor- mally intelligent people that his first generation phonograph was indistinguishable from real voices and instruments. He and others mounted live vs. reproduced tests in concert halls. They were all successful (Toole, 2008, Section 2.1). But wait, perhaps listeners were responding to the excellent acoustics of the halls (the recordings were “dead,” without reverberation). As several studies have shown, envelopment is a critical quali- ty of a good hall, and therefore of anything produced—or reproduced—within it. If this is not a factor, we are forced to consider that there has been no consequential improvement in reproduced sound in the past century.
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