Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/3/84; site teddy.UUCP Path: utzoo!decvax!genrad!panda!teddy!rdp From: rdp@teddy.UUCP Newsgroups: net.audio Subject: The ear vs. instruments Message-ID: <1382@teddy.UUCP> Date: Thu, 3-Oct-85 13:19:33 EDT Article-I.D.: teddy.1382 Posted: Thu Oct 3 13:19:33 1985 Date-Received: Fri, 4-Oct-85 15:30:23 EDT Reply-To: rdp@teddy.UUCP (Richard D. Pierce) Distribution: na Organization: GenRad, Inc., Concord, Mass. Lines: 195 Summary: [] This is real long, so bear with me... The debate is flaming once again over the value of laboratory measurements versus the "golden ear". Having had a lot of experience in lab measurements of various hi-fi components (about 7 years worth) as well as having been involved in research into audibility of distortions, my two cents worth is being cast upon the waves. First let me state, at the great risk of being flamed, that I find the concept of the "golden ear" to be a complete crock. Some of the most highly regarded "golden ears" are so inexperienced in listening to live music that it is ludicrous the weight their opinioins are given. Having said that, let's look at some summaries of the opinions expressed on the network. 1. "poor frequency response is the major contributor to lack of fidelity" 2. "Harmonic distortion does not contribute at all to the sound of hi-fi components" 3. "The great difference in sound between amplifier A and amplifier B can not be attributable to the differences of .01% and .1% in distortion we measured" 4. "Since this set of measurements don't differ greatly, and the components sound wildly different, then the audible differences can NEVER be measured in the laboratory" And so on, ad infinitum. When I was in the audio business, the store I was the technical manager of had the policy of measuring, as completely as possible, EVERY single piece of equipment that even came near the store. That included every piece that was sold. For electronics, as an example, we measured THD at full power, 1/3 power, 1 watt, 10 mW, and at 20, 200, 2000, and 20000 Hz. IM distortion was measured at these same power levels. Transient response was evaluated from input to output (including phono sections). Reactive load driving and recovery from overload was tested. On some selected units, transient modulation characteristics were tested. When THD was done, often a complete narrow band spectrum analysis of the distortion components was done. The same for noise, and on and on and on. I was able to collect a vast amount of verifiable, correlatable data on the measured performance of commercially available hi-fi components (probably totalling some 5000 to 6000 units). Some immediate (and, hopefully, non-controversial) conclusions can be drawn from this data: 1. MOst units barely squeeked by the manufacturers specs out of the box, with the exception of tape recorders (of all types, cassete, reel- to-reel, etc.), which failed, with few exceptions, miserably. 2. Most units could be made considerably better by simple tweeking. Tape recorders are the biggest beneficiaries here, followed by tuners. 3. Most units produced by the larger manufacturers were consistantly better adjusted than those of small, esoteric, manufacturers. This was most true of power amps. Those from many of the audiophile companies were dismally adjusted, most never met specs. The reason is probably that they don't know how do design amplifiers that could be shipped properly. Now, what has all this to do with the sound of various components? Well, as presented, not a whole bunch. But it does establish an objective base from which to proceed (before flaming me for pre-conceived notions, read on!) Let's take an example of two amplifiers of similar characteristics that sound decidedly different (I realize they are somewhat antiquated, but I do have quite a bit of experience in this particular comparison, and it's validity transcends the age of the experiment). The crown DC-150 was a 75 watt/ch power amplifier with fairly wide bandwidth and low distortion (measured at below .05% THD for most cases). The LUX M1500 has very similar specs. Rather than deal with the similarities, let's look at the differences. The Crown has a higher damping factor and a somewhat wider bandwidth. The Harmonic distortion figures at full power are lower for the Crown than for the Lux, but not by a lot. In listening tests, about 85% of the people listening regarded the crown as being "edgy" or "brittle" or "hot", or "very detailed" or "tiring", whereas they regarded the Lux as "sweet", "reticent", "unagressive" and the like. Simple THD, frequency response, IMD, etc. measurements revealed little differences, especially when measured the way the manufacturers did. However, very large differences were measurable at realistic listening conditions. The most complaints about the Crown occured when listening to quite passages. Under these conditions, the Crown did have more THD than the Lux, but it still was low (at 10 mW, the THD, excluding noise, was approaching .2%). There was, however, a striking difference in the makeup of the distortion components. In the case of the Lux, most of the distortion products were confined to the second third and fourth harmonics, totaling about .04%, whereas in the Crown, the distortion products consisted mainly of third, fifth, seventh, ninth, etc, etc., and the spectrum continued as far up as the fifteenth harmonic in some cases. It was noted that the vast majority of the distortion occured as a result of dis-continuities at the point where the output stages were switching from positive to negative output and back again (That ol' devil, crossover distortion!) Additionally, one of the transient tests we performed, which consisted of taking a 5Khz sine wave at about 1 watt, and occasionally imposing a 10 watt (or greater) 10 mS wide cosine pulse, resulted in about .1% modulation from the Lux, but 20% (yes TWENTY) modulation in the Crown. Note that in both cases we were nowhere near starining the amps power wise. Also note that the demodulated waveform in the Crown did not closely resemble the pulse, rather it showed a fast exponential rise, followed by a slow exponential decay, and all this delayed by a few milliseconds (maybe heating of junction effects? ). We did find that static damping factors don't mean s**t. We found, however, that the crown, which had a damping factor of (as I recall) 150 at 20Hz, had a damping factor of about 5 at 5 Khz, and under transient conditions, it was lower still. The Lux managed to maintain it's factor of 50 out to 10 Khz. It was interesting to see what happened to such things as THD and IMD as a function of power. Both amps were quite low in the range of 3 watts to near clipping. However, below that, the Crown's distortion rose monotonically with decreasing power, whereas the Lux's remained fairly constant until the point where it was totally swamped by noise (milliwat and lower levels). What does this all prove? Well, to me it demonstrates that if we are hearing differences that we can't measure, than we simply aren't measuring everything, or we are not measuring them correctly. We simply can't stand back and declare dogmatically that THD doesn't mean anything, or frequency response is everything, or nothing. The ear, is indeed, a complex measuring instrument, which reveals qualitative measurements. Laboratory instruments reveal, on the other hand, qualitative figures. The two are certainly correlatable as long as sufficiently precise, accurate, controlled, and unprejudiced experiments are performed. It has been my sad conclusion that the audio world is not interested in this type of research, nor of the commercial application of the results. Too many of the esoteric companies would fall flat on their faces in any fair technical forum. The point to hi-fi, in my view, is to, as accurately as possible, re-produce the information provided to us by the media-mongers, however dismal that may be. I have found, universally, that this goal, combined with good media, most closely duplicates the musical experience of the live performance. Then, if you accept this definition of accuracy, laboratory instruments are admirably suited to measuring the deviation from this accuracy, because they are consistant, untiring, and unprejudiced. They are not swayed by media and guru hype, especially when a consistant measuring procedure is applied. This, combined with a scientifically controlled, unbiased listening test, results in a very good, predictable, correlation between sound and measurements. In fact, what often happens is that the subtle audible differences seem to magically vanish, never to return, when a controlled experiment is performed. About 12 years ago, an interesting measurement technique was described by (I believe) Peter Walker of QUAD, U.K. in "Hi-Fi News and Record Review". In the article, he described a technique of measuring amplifiers by what he described as a bridge technique. Simply stated, the output is compared to the input, via phase and delay compensating network, and the resultant output is a direct measure of the inaccuracy of the unit. We applied the same technique to the above experiment, and, lo and behold, the Crown would reveal HUGE errors when people were bitching about it (low powers, etc). The technique would not, unfortunately, reveal what kind of errors, just their magnitude. (Note that in our case, we eliminated the phase and delay compensation network, on the theory that any error is significant. Given the bandwidth of the Crown and the Lux, it was deemed unnnecessary anyway). The nice thing about this particular technique is that the signal can be anything, including music. Many research papers have been published in journals such as the Audio Engineering Society, the Journal of the Acoustical Society, and so forth, regarding the audibility of particular kinds of distortion. Most audiophiles do not have either knowledge of or access to these articles, and many of them would find (as I occasionally do) them to be quite incomprehensible. But the fact remains that there has been much work done on the audibility of these effects, and much of the denial of such stems from lack of knowledge of these researches, or the inability or unwillingness to perform controlled experiments without prejudice. The one article that comes to mind that I found most amusing is the one person who over a period of a half an hour substituted of few conponents in his CD player, and then noticed a "dramatic" improvement in the sound of the unit. Two serious challenges arise against the validity of his claim. First, it has been more than adequately demonstrated that the acoustical memory can be quite poor over the long term (more than a few seconds). Secondly, having invested in a CD, these ridiculously expensive replacement components, a lot of time, effort, sweat, burned PC board traces and fingertips, and lots of weeping wailing and gnashing of teeth, I would not expect any rational person to be willing to admit that there was no difference, or even a negative improvement. Damned if I would be so honest as to admit how stupid I was for screwing something up (although, now that you confront me with it, I have screwed up quite a few things in my time!). So folks, let's be more scientific about things. Every "golden ear" who has tried to demonstrate, under fair, controlled conditions, that such and such a unit sounds such and such a way, has failed to duplicate the results. The comment one gentleman made about "the differences vanishing under double-blind testing" is well taken, and quite accurate. Dick Pierce Brought to you by Super Global Mega Corp .com