The answer to this question, in my opinion, has to start with an overview of quite an interesting phenomenon that is responsible for appearance and dissemination of superstitions and myths in High End Audio. I’m talking about a specific conception that, by now, has become deeply rooted in the minds of audiophiles and many professionals. This conception promotes the absence of correlation between the objectively measured characteristics of the sound reproduction equipment and the results of subjective listening.
In order to save some space, I will limit my discussion to amplifiers, although everything I say below applies to any audio component.
The tenacity of these myths has to do with consistent adhearing to the-now-traditional methods of audio system evaluation, methods that use generally accepted formal parameters from product specifications. This is particularly obvious in reviews in specialty audio magazines that do both the objective and subjective tests, and that echo the traditional approach to evaluating a component. There are plenty of reviews on certain amplifiers which are, even by the least demanding standards, not very good in the opinion of test engineers (who do the objective measurements) but which are sometimes praised to no end by the reviewer (who does the listening part of the review), and vise versa.
Such discrepancies between measurement results and listening evaluation are the direct result of a lack in the field of audio electronics of objective criteria that would allow us to evaluate the component sound quality without auditioning it.
I will try to clarify the essence of the above issue in a context of my research conducted over the years and within the limits of the “human hearing mechanism” theory which I developed in the course of this work. I apologize for the gross oversimplification in describing the principles at the basis of my design philosophy and their application because the mathematical apparatus involved is quite complicated and is well beyond the scope of this answer. What matters here is the person’s understanding of the real and objective tool for evaluating the sound quality, not techno-babble behind the tool. In this oversimplified description I will try not to throw the baby out with the bath, so to speak.
In my opinion, one of the key steps that would bring us closer to the objective evaluation of the measured parameters/sound quality of the amplification gear and the establishment of unambiguous correlation between the two is to introduce a new notion that would allows us to interpret the measurement results and predict the sound quality of the measured piece of equipment without listening. I take the liberty of labeling such a notion the “Absolute Linearity of a System” (ALS) because no commonly used terminology exists for describing this concept. Since, in general, the ALS is a function of a certain number of variables, explaining the influence and interaction of all of these variables is not realistic within the limits of the answer. Therefore, for the purpose of clarifying one of the aspects of ALS, I’ll concentrate on the interaction of only two variables which are commonly used for component evaluation, and to which much significance is ascribed in the technical specs of any amplifier. These two variables are also a subject of most diverse interpretations in comparing subjective (listening) and objective (measurement) results. Keep in mind that we take these two variables out of context, and ONLY for the purpose of demonstrating certain aspects of the ALS.
These two variables are:
• TOTAL HARMONIC DISTORTION (THD) vs. FREQUENCY at various power levels and
• THD vs POWER (usually, these measurements are taken at 1KHz, although it is necessary to take them at least at three frequencies: 20Hz, 1KHz and 20KHz, or sometimes at 10KHz instead of 20KHz)
Figure 1 above is a graphical expression of THD vs. FREQUENCY of a so-called ideal amplifier (ideal in a sense of faithfulness of sound reproduction).1 As you can see, this parameter is a straight line at each power level; it is constant and does not change with frequency.
Figure 2 above is a graphical expression of THD vs. power of the same so-called ideal amplifier.1 As you can see, this curve has the same shape at all frequencies within the audio frequency range; THD smoothly increases with an increase in power.2 (Description of the behavior of this curve lies beyond the scope of this answer.)
1. Again, a strict proof of this fact is beyond the scope of answering this question.
2. In a so-called “ideal” amplifier all three curves in Fig.2 must merge into one line, in other words, they must be absolutely identical. I spread them out for easier viewing.]
Both of these curves (in Fig. 1 and Fig. 2) are, of course, part of the three-dimensional representation of the function of two variables, which somehow can be expressed in this manner:
THD=Function (power, frequency)
If the corresponding characteristics of a real-world amplifier are close to those described above, then the combination of THD vs. FREQUENCY, THD vs. POWER and some other parameters become the variables of another, more refined, system of parameters. This higher-level system absolutely unambiguously describes the sound quality of any amplifier based on its formal parameters as they appear in manufacturer’s specs.
As mentioned earlier, it is not feasible here to review all variables. However, in addition to information about THD vs. FREQUENCY and THD vs. POWER, it is absolutely necessary to at least have information about the HARMONIC DISTORTION RESIDUE (HDR) at various frequencies within the audio frequency range and at various power levels. Keep in mind that very rigid limitations apply to the form of the HDR, limitations which are imposed on the number of harmonics and the ratio between the values of different harmonics.
Once these requirements are met, THD vs. FREQUENCY, THD vs. POWER, information about HDR and some other parameters3 become objective tools in evaluating the sound characteristics of an amplifier. We have to keep in mind that we should look not as much for the value of these parameters per se4 but rather for their graphical or analytical expression because the value itself does not carry information which is traditionally ascribed to it. What matters is the difference between the behavior of a so-called ideal system and the system under evaluation. Again, the “Absolute Linearity of a System” is the ability of an amplifier to exhibit parameters close to those of an ideal amplifier.
3. Those presented in an amplifier’s specs and which, in the way they are presented, mean very little and are often confusing in their correlation with the sound.
4. The value of these parameters, in general, are more applicable to clarifying purely technical aspects, such as evaluation of the amplifier’s topology, and pointing out the types of active elements utilized (solid-state devices or vacuum tubes), etc. Of course, these data provide certain information about the quality of sound. However, when taken out of context and being incomplete, these same data is what brings about the well-known “paradoxes” in comparisons of the objective vs. the subjective.]
What’s interesting is that if a hypothetical engineer were to implement these principles, he would sooner or later arrive at a limited number of topologies conforming to the described requirements. On the way to such a goal, this engineer would have to discard many conventional topologies, some of which are quite beautiful and appealing in layout.
Please note that when one tries to implement these methods into the amplifier design without any tricks, one realizes that the cost of production of such a unit is quite high. Which is the case, of course, with all real things in this world.
From my point of view, utilization of these methods sets very high standards in equipment design and, in turn, leads to a increase in production cost which determines a correspondingly high retail price. At the same time, we are able to hear immediately the difference between the system based on my design principles and other systems.
LAMM equipment represents a life-time investment. It actually saves one a lot of money in the long run by eliminating the need to constantly upgrade one’s system.
To corroborate my point and to prove that I have been able (to a greater or lesser degree) to implement the principles described above, I have attached the FILES containing the results of objective measurements of certain parameters for one of my designs, single-ended amplifier model ML2. All these measurements were conducted by an independent party, Mr. Bascom H. King of BHK Labs (email@example.com). I picked this amplifier as an example on purpose because it is quite expensive and because it is a single-ended design which traditionally measures very poorly.
The ML2 has already been reviewed by four different magazines (click here for a list of reviews).
In the future I will continue the discussion of this issue with the purpose of showing the unambiguous correlation between the methods I use in designing the ML2 (and other models), measurement results, sound quality, and the price that I have to pay to attain various results in various models…
© 2018, Vladimir Lamm. All rights reserved.