Is Objective Correct?

By Eric K. Pritchard

Please note that this article has appeared in Audio Electronics (Volume 2, 2000) and is consequently is available for publication only with the proper reprint credit to Audio Electronics.

I. Introduction

The audio world is torn between those who live by the objective measurements of audio performance and those who judge audio performance by careful listening. The objective group has created a variety of arguments and electronic tests based upon the assumption of the linearity of hearing or upon the ability to detect a difference between the device under test and a standard. The subjective group, unfortunately, are left with an inadequate, non-standardized language to express their listening impressions. As the history of audio will testify, this has been a losing battle for the artistic nature of audio as the "objective" engineers follow their paradigm that amplifiers are supposed to replicate their inputs without embellishments. However and unfortunately, it is some of those embellishments that artists prize. They chose equipment based on those embellishments. However, audio has progressed to the evermore sterile, cold, thin, lifeless, and sometimes harsh character while the subjective artists prefer warm, fat, full-bodied, and alive.

Some years ago, I decided to translate the wonders of tubes to solid state and doing so, I ran into the confusion between engineering paradigm and the subjective desires. Ultimately, to successfully translate the character of the vacuum tube, I had to open my engineering mind to different concepts. I had to re-examine my engineering background and mind sets.

My degrees are in Mathematics and Electrical Engineering. Although there is a lot of mathematics in engineering, there is very little of the formality of mathematics in engineering. The formality of mathematics is based upon the full and complete statement of assumptions, theorems, and corollaries. Engineering, however, proves a point by making assumptions along the way and later often forgetting those assumptions. Where mathematics builds on the firm foundation of precise logic, engineering often is not so precise. On the other hand, mathematics usually has the luxury of time while engineering must make sense of complex devices on the way to meeting a production deadline.

Carlos Santana introduced me to the subjective side of audio when I was visiting the Paul Reed Smith Guitar factory in 1987. He explained that my first attempt at a solid state guitar amp was like "white wine" and "glass" and not like "red wine" or "flesh". Later, Al Di Meola further confused me by declaring that my third attempt was "dead" in spite of functioning. I took these rejections seriously since I was determined to make the greatest guitar amp ever with solid state components. However, they did not provide much of a clue because they were not couched in the language of engineering. But I did know that something was wrong. I eventually reexamined my engineering schooling and the two decades of practicing the engineering. These are my observations:

The Engineering Paradigm

An engineering paradigm is amplifiers should replicate their inputs without any embellishments. That "truth" has been established for three score and more. This paradigm is embedded in the Total Harmonic Distortion (THD), Intermodulation (IM), frequency response tests, etc. and quoted in most audio equipment specifications. But is it correct?

Voight vs. Fletcher-Munson

The paradigm is not completely correct. The example of true fidelity in Radiotron Designer's Handbook [1] came from Voigt [2]. The situation of a listener in a room with a window on a concert hall was claimed to be the nearest approach to true fidelity. However, the attenuation of the hole combined with the non-linearity of hearing as measured by Fletcher-Munson [3], produces a different apparent frequency response. That is hardly true fidelity. In fact, the loudness control was invented to compensate, at least partially, for this hearing characteristic. Further, since the apparent loudness is non-linearly related to the sound pressure, the variations in concert levels will be perceived differently.

Paradigm vs. Jason

Audio notables Stanley Lipshitz and John Vanderkooy [4] proposed "accuracy" as the hallmark of audio even though much of audio recording processes are not chosen because they are accurate but because they sound better or otherwise preferred. The measure of accuracy was the detectability of any difference between the device under test and a standard with, of course, every effort to make such a comparison reasonable. Of course, this is a restatement of the engineering paradigm.

Mr. Jason noted [5] that the judgment of highly complex audio signals of loudspeakers in listening rooms "does not lend itself to definition". Jason recommends "preference" be the basis of judgment.

The paradigm appeals to the intellect while the subjective preference appeals to the emotions. However, emotions often have the greatest impact upon decisions [6] while the intellectual advertising appeal is inefficient. The accuracy of bland food is not as appealing as food with spices and sauces, so long as they are not over done.

The Paradigm vs. Terman

The highly respected Dr. F.E. Terman wrote, "The ear has a non-linear response to sound waves of large amplitude. The result is that with powerful sound waves the ear produces harmonics, as well as sum and difference tones which are not present in the original sound and yet are actually present in the hearing organs and are perceived by the brain."[7]

Dr. Terman also explains the phenomenon noted by vacuum tube proponents: that tube amplifiers seem to have an extra octave of bass. This is probably created by "subjective tones". "The apparent pitch of a sound is not changed by removing the fundamental frequency since the harmonics combine in the ear to produce a difference frequency tone [i.e. the missing fundamental]." So the fundamental with harmonics may be understood by the brain as still lower frequencies.

The paradigm is also not completely logical because it insists on a linear system for human hearing, which is not linear [3]. While accuracy is laudable, the point of measurement is not correct, only simple. The measurement should take place after the hearing process - not before. With certain reservations, listening is believing.

The Paradigm vs. Hamm

There are customers whose hearing tells them that amplifiers with certain embellishments in reasonable quantities are better than amplifiers without embellishments. In addition to artists, there are some audiophiles and recording engineers who appreciate appropriate embellishments. Russell Hamm [8], a recording engineer, was frustrated with the then new transistor-based recording equipment, microphone amplifiers in particular, and investigated. He determined that peak microphone levels would distort the microphone preamplifiers. The tests mentioned above did not provide any reason why the old vacuum tube microphone preamplifiers sounded better than the new and "better" solid state preamplifiers. Mr. Hamm, who later became president of the Audio Engineering Society, ultimately devised his own test: plotting the percentages of each harmonic as a function of overdrive. The resulting plots distinguish the various technologies tested: triodes, pentodes, transistor (2 types), and operational amplifier. The triode vacuum tube microphone preamplifier embellished with its unique harmonics was judged the best.

Perhaps, a word about assumptions is needed here because this story involves two groups speaking the same language but with different assumptions. The designers believe that their circuits are going to be treated with a certain reverence and not be over driven. Hence they can apply feedback of all sorts with only one thought in mind: stability. However, the recording engineer often would let the preamplifiers clip so that the noise floor would be lower. The feedback and biasing of transistor amplifiers reacted harshly to going beyond the assumed range and into clipping. The amplifiers were not designed for that.

The Paradigm vs. Accepted Distortions

The paradigm is not completely logical in view of general audio practices. Recording has many steps that alter the character of the signal. The recording engineer and producer chose various types of equipment to make the end product sound better. Microphones are chosen for their sound and different microphones are typically used for different instruments. Tony Bongiovi, of the Power Station in New York, preferred the U47 (a famous, revered, old Neumann studio microphone): "It has to do with the harmonics and the way they combine with soft music. On loud passages, it overloads some…"[9] The microphone signal is then amplified by a preamplifier which is also selected for its character, just as Russell Hamm [8] did. Then it is compressed, equalized, mixed, and recorded; all of which are also picked for how they sound. The compressor introduces scale distortion. The equalizer introduces frequency distortion. Even the recording systems were used for certain effects. Later, the playback systems include volume controls (scale distortion) and tone controls (frequency distortion). The intentional distortions of both recording and playback belie "true fidelity" and make the inclusion of some "musical" harmonic distortions reasonable - a matter of taste. In fact, they can make the audio sound loud even when it is not so loud.

The Paradigm vs. "Everybody Hears Differently"

A common response to objections to the engineering paradigm is that everyone hears differently [10]. That really requires a review. The excuse for a single concept paradigm is that people apparently listen and make judgements differently. There are two possible solutions for this dilemma: either people need a choice of solutions to fit their individual taste or their language for describing what they hear varies considerably. One definite conclusion can be drawn, however. The paradigm does draw complaints.

One explanation for so many descriptions of listening experiences is that there is no standardization of the descriptions of aural sensations. How does one evaluate "distorts too fast", "three-dimensional" or "sounds like" glass, flesh, white wine, red wine, dead, or alive? No one with a predisposition for the paradigm would give such descriptions a second thought because people hear differently, or they are just nostalgic, or they reflect some other human frailty.

The Paradigm vs. Weighted Total Harmonic Distortion

The standard, non-weighted Total Harmonic Distortion test does not accurately predict listening displeasure. An amplifier with a high THD can sound better than one with a low THD. This phenomenon was tracked down to the influence of high order harmonics. Since their influence upon listening displeasure is greater, they should be given more weight. Consequently, weighted THD was developed. One weighting function has coefficients equal the harmonic number and another is equal to the square of the harmonic number. The latter actually produces numbers that correlate better with listener appreciation tests [11].

None of these tests place any positive value on any harmonic at any level. Thus, even weighted THD does not accurately predict artist appreciation. There is a value to some harmonics at some levels as proven by the many artist preferences.

Electronic Enigmas and Linguistic Mysteries

The engineering community has declared that transistor circuitry has been beyond tubes for many years, at least according to their paradigm. However, many artists do not agree. They have long held that tubes still are the measure of artistic performance. Unfortunately, artists and engineers are two peoples separated by linguistic misunderstandings and the tube phenomenon has remained an engineering aberration until the development of my technology.

With no guidance from any source and no understandable artist critiques, my progress depended upon realizing the limitations of human hearing. The ear and mind are quite adept at diagnosing situations for which it has been trained. However, since artistic amplifier development is new ground, the listening and playing tests did little more than indicate failure. Getting a critique that provided a clue was unusually lucky.

Conclusions

The engineering paradigm for amplifiers is that they should replicate their inputs without any embellishments. Tests have been created to grossly measure these embellishments. These tests are the well known: Total Harmonic Distortion (THD), Intermodulation (IM), Frequency Response, etc. The aim of these tests is to make the amplifier linear and flat by reducing the embellishments to zero.

Artists, however, pick their amplifiers on the basis of their embellishments: Warmth, Resilience, Body, and Life. In their judgment, engineers produce amplifiers that are Cold, Stiff, Thin, and Dead. Unfortunately, the linguistic mysteries virtually preclude communication between artists and engineers. They simply do not think in the same terms. Engineers think of amplitudes and frequencies while artists relate to sensory impressions. And to make the linguistic separation from engineers worse, artists usually translate their hearing impressions to the languages of other senses.

The engineering paradigm also hinders communications with artists. Engineers piously cite their objective tests that show that their paradigm is correct and they declare that the artists' observations are subjective or worse, nostalgic or dismiss different observations with differences in hearing ability. The difference between these positions has been reexamined and found the engineering paradigm lacking a strong, logical foundation. Is a measurement truly objective if its foundation is subjective?

If the formality of Mathematics were practiced in audio, the paradigm would have been discarded for a more accurate concept long ago because these counter-examples show the paradigm to be only partially true. However, the informality of Engineering will accept partial truths because they seem to get the job done. Unfortunately, these partial truths often become paradigms and are put above reproach.

Perhaps the passion engineers have for their paradigm is a frantic orthodoxy that was explained by Reinbold Niebuhr as "never rooted in faith but in doubt. It is when we are not sure that we are doubly sure."

References

1. Langford-Smith, Radiotron Designer's Handbook, Fourth Edition, 1953, pg. 603.

2. Voigt, P.G. A. H., "A Conversational Idea from England", Audio Engineering, 34.10, October 1950.

3. Langford-Smith, Radiotron Designer's Handbook, Fourth Edition, 1953, pgs. 826-827.

4. S. P. Lipshitz and J. Vanderkooy, "The Great Debate: Subjective Evaluation", Journal of the Audio Engineering Society, vol. 29, pp. 482-491.

5. M. Raymond Jason, "Design Considerations for Loudspeaker Preference Experiments", Journal of the Audio Engineering Society, Vol. 40, No. 12, pg. 979-995

6. Barry Feig, Marketing Straight to the Heart, American Management Association, New York, 1997.

7. Dr. F. E. Terman, Radio Engineering, McGraw-Hill, 1947, pg. 863.

8. Russell Hamm, "Tubes Versus Transistors - Is There An Audible Difference?", Journal of the Audio Engineering Society, May 1973.

9. "Neumann - the History of Tube Condenser Microphones", Recording Engineer, February 1980.

10. G. Randy Slone, High-Power Audio Amplifier Construction Manual, McGraw-Hill, 1999, pg. 17.

11. Langford-Smith, Radiotron Designer's Handbook, Fourth Edition, 1953, pgs. 610-611.

The Author

Eric K. Pritchard is an artistic engineer with degrees in Mathematics and Electrical Engineering. He is a prolific inventor with 32 U.S. Patents plus many foreign patents. Nineteen of these patents plus others still pending are in the general area of translating and exaggerating the non-linear vacuum tube character to solid state. Mr. Pritchard is the founder of Pritchard Amps, a West Virginia company in transition from research of artistic amplifiers and microphones to their production. For more information and sound bites check www.pritchardamps.com.