Assumptions in Audio Design

High-end audio is both stimulating and perplexing because of the diverse assumptions about the goals of sound reproduction and the process by which one achieves those goals. We at Anedio start with a set of assumptions about how to optimize an audio system for the most faithful reproduction of music. Other designers start from different sets of assumptions. These fundamental assumptions shape the design process and how the whole system is conceived.

Our fundamental assumption is that an optimal solution requires a holistic approach -- an artful integration of analysis and listening in view of the whole system. It is both art and science, in which we try to keep the following triad in mind: (a) whole system, (b) measurement & analysis, (c) extended listening.

(a) Whole System

Perhaps, the most important factor is to consider the system as a whole, and not merely as an assembly of individual components. Often a designer would invest enormous amount of resources in tackling a single issue, only to run up against diminishing returns. Without a holistic view of the sound reproduction system, it is easy to forget the real bottle neck that limits the performance of the whole system. In the language of optimization, each designer tends to focus on achieving a local optimum for a single product, while neglecting a global optimum for the audiophile.

For the consumer, to gain a holistic perspective is even more difficult since the marketing of high-end audio is highly fragmentary, and each manufacturer claims that investing in their equipment will make the most difference. Unfortunately, the interpretation of such advertisements is left up to the consumer.

We need to learn to set our course by the stars, not by the lights of every passing ship. -- Omar N. Bradley

In order to achieve a global optimum, what is required is an integrative approach, considering all the elements in the audio reproduction chain -- the source, preamps, power amplifiers, cables, crossovers, loudspeakers, and the room. Integration is the most difficult, yet the most rewarding task. A well-integrated audio system can reproduce recorded music with exceptional fidelity at a surprisingly low cost.

With the holistic view of the system, the designer can invest more resources on those parts that have greater impact on the experience of listening to music. In our view, the two most significant factors in shaping the overall listening experience are the loudspeaker and its interaction with the room. Especially critical is the loudspeaker's radiation pattern over a wide frequency range and how it illumines the room. Of course, the source and the amplification chain are important, as we strive to perfect them, but they must be seen as part of the whole system, serving the greater purpose of reproducing recorded music faithfully.

(b) Measurement & Analysis

Another aspect that we keep in mind in the design process is that our listening experience must be informed by objective reality. Often, a perceived improvement might actually be a euphonic aberration due to a slight deviation in the frequency response or an addition of the second order harmonic. It may sound euphonic, and we may even prefer that sound, but it has little to do with accurate sound reproduction. Objective analyses supported by meaningful measurements would temper the tendency toward imaginary interpretations of the differences we perceive in listening.

We are not satisfied with the assertion that an audio component measures well but sounds terrible. The discrepancy usually lies in the limitation of the measurement, the interpretation of it, and the artificial condition under which it was administered. The standard measurements, such as THD+N (Total Harmonic Distortion + Noise), by themselves, are inadequate. A single number simply cannot capture the reality of psychoacoustic phenomena or the complexity of underlying distortion mechanisms.

Measurements that can meaningfully represent slices of reality need to be multi-dimensional, not merely a single point. For example, FFT (Fast Fourier Transform) spectrum, a commonly used frequency-domain analysis, is a 2-dimensional slice, cut along the amplitude and frequency plane. This 2-dimensional information is more meaningful than a single number since it reveals the shape of the noise floor and non-harmonic noise as well as the detailed behavior of harmonic distortion. It also opens up room for nuanced interpretation, as higher-order harmonics and non-harmonic noise are more objectionable to auditory perception than 2nd and 3rd order harmonics.

Measurements must also reflect the typical condition in which the audio component will operate. A component may perform well on a test bench, but when it is connected together with the rest of the system, it may falter because of its undue sensitivity to ground-loop noise. In order for measurements to be meaningful, the condition must not be artificial, but reflect a realistic setup found in typical homes. When properly administered in a realistic condition, measurements do represent slices of what we actually hear.

Every creator painfully experiences the chasm between his inner vision and its ultimate expression. -- Isaac Bashevis Singer

Having said this, we also believe that sound reproduction and psychoacoustics are incredibly complex processes with a multitude of variables that interact in ways that are not always understood. Any measurement or analysis is bound to be reductionistic, merely a slice of the reality. The process of reduction is useful in that it allows the designer to focus on a manageable aspect and to understand the underlying physical principles. As long as one understands its limitations, it can serve as an essential tool for guiding the design.

(c) Extended Listening

The third essential aspect that we keep in mind in the design process is extended listening. The human ear is an incredible instrument with an extraordinary dynamic range, capable of hearing minute details while absorbing thunderous passages. It also has the amazing ability to perceive space and to locate the sources of sound in 3-dimensional space. We emphasize extended listening because something that is not immediately apparent might become more recognizable as we listen to a wide variety of music over an extended period.

The ultimate reference point for the design of an audiophile system is the live, unamplified, and unprocessed sound. As Linkwitz insightfully notes, the art of listening is different from the art of wine tasting. Even though both disciplines have subjective elements, listening has an objective reference point, namely, unamplified and unprocessed natural sound. It is to this reference point that we must return over and over.

We need to develop the senses for live, natural sound, and let our memory of it serve as the objective basis for listening tests. This means regularly attending live concerts to train one's ears. It does not need to be a first-class orchestra or jazz band. Even in student recitals and in less than glorious ambiences, much can be learned about the characteristics of live, unamplified sound. It can even be in daily environment -- the sound of birds chirping, cars passing by, school choirs singing, and kids playing. Once we train our ears to live, unamplified sound, we are in a better position to evaluate the reproduced sound of audio systems.

The ultimate goal of designing audio equipment is the enjoyment of music. When all is said and done, the bottom line is the emotional impact of the music reproduced through the system. We cannot measure the beauty of music with test equipment. At its best, high-end audio is about those moments when the equipment fades in the background and all that remains is the echoes of awe and wonder.

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