I agree. I was make an amplifier with 0,06% THD at 1kHz/8,2 ohm 100W rms about 14 years ago. The amplifier have 120W rms max. power. It can sound accurate or not, good or not, depend on other instruments in the system.
Even, right now I can make simulation of an amplifier that have THD under 0,001% at 1kHz, have very high slew rate. Unfortunately, now I do not have THD analyzer.
As do I, but probably by means of a more rewarding methodology - actually doing them.
The effort and training required to to blind tests of audio gear is probably a little below average by modern standards.
BTW the team that developed ABX back in the 70s was composed of 3 PhDs, 2 BSEE or the equivalent, and 1 BS Math.
Interesting, but seriously flawed.
In the cosmic scheme of things, the 10 second delay vastly reduced the probable sensitivity of the tests. Anything much past a second is a death's blow.
And there is the problem of relying on opinions about what sounds better, which is about as fatal.
Depends on the circumstance.
If the nonlinear distortion is audible, then THD fails to tell you much about the details of the nonlinear distortion, and those details can be very helpful.
If the nonlinear distortion is inaudible, then THD tells you everything that you need to know, which is to move on.
Of course I realize that I am among people who do irrational things like relying solely on sighted evaluations relating to subtle differences and don't believe that nonlinear distortion can possibly be inaudible. It is all the same problem.
Some info from Earl Geddes on the THD/non-linearity topic:
Thread:
http://www.diyaudio.com/forums/multi-way/121253-geddes-distortion-perception.html
Thread:
http://www.diyaudio.com/forums/multi-way/121253-geddes-distortion-perception.html
I've challenged Earl in person on that topic (which is echoed in the AES paper he wrote with his wife) .
The known common exception to 0.01% THD being audible relates to forms of distortion such as crossover distortion and TIM/SID that are very rare in modern audio gear as a practical matter.
I have to admit that even with my archives of measurements of legacy gear, I know of no practical instances of either with properly operating gear.
If you choose to nit pick you can find flaws in just about all testing. The big ones can be mitigated by time and money. When we did serious testing at work, both were part of the test proposal. A line item for all product or new technology development is testing, test time and money budgets. This is a BIG hitter in IC development and where I spent the last 10 years of my career.
As we learned, you fit the testing to the scope of the job. You don't ask 2 guys to verify a new product the day before you release it, and you don't need an army of engineers to qualify a part that's only used in a prototype.
I stated from the beginning that it was flawed, and I stated some of the reasons. This was about a group of guys that were about to build some SE amps who needed to buy about $2500 worth of OPT's. All of the test OPT's were electrically evaluated beforehand, and the results were known to the participants. That's how we narrowed the list to 5 OPT's. We agreed on the testing, did it, and were happy with the results. If I was to make the same purchase today, and had the same resources available, I would do it the same way again, except for speaker choice.
This happened 8 years ago. The Motorola plant had since closed, Motorola Mobility is now Chinese owned, and all of the participants are scattered across the country, so it won't happen again.
A single THD number doesn't tell you much about how an amp will sound.
It is a good reference point to use when comparing the power output capabilities of two amps of the SAME topology.
I have a 1 watt amp and a 2 watt amp. Can you state that one makes 2 times the power as the other with any certainty? NO, they could even be the same amp under different test conditions.
I have an SE tube amp that makes 1 watt at 3% THD. I have another SE tube amp that makes 2 watts at 3% THD. Now I can make a general comparison about the power output of these two amps.
This, and the ease of measurement, is the reason I quote the THD numbers. It is better to have an FFT analyzer hooked up to see the harmonic distribution, but even this can hide things.
We don't listen to single sine waves, and THD usually brings along it's ugly cousin, IMD, and a few other guests. So we test with two tones and observe the harmonic spectrum.
In linear RF power amp testing for CDMA and LTE we found that two tones weren't enough so we used FIVE tones......
Better, but with live test signals there can be errors in time (phase or frequency shift caused by group delay errors), without a corresponding error in amplitude, so EVM (error vector magnitude) testing was developed. That analyzer costs about $50K so it hasn't made its way into the audio world yet.
At what level does nonlinear distortion become inaudible.....That depends....a lot. We tend to test things under static conditions, yet listen to very dynamic music. A steady state distortion number, or set of numbers including the details of each harmonic and IMD product, does little to explain how the DUT behaves under dynamic conditions, or how it sounds with dynamic music.
The duration as well as the magnitude of a distortion event has a large effect on its audibility. A single clipped peak of 10% distortion can go undetected if the amp recovers instantaneously with no overshoot or ringing. Yet, a smaller event of less than 1% may be obvious if it messes up the timing or amplitude of the surrounding signals.
Music consists of several instruments playing at once. If the bass guitar (cello or whatever) clips on peaks without causing any other artifacts, it may not be noticed, or it may be noticed, but not objectionable. If that clipping event causes IMD in the overlapping vocals.....yes it WILL be heard.
Many amps behave differently in this regard, and that is why many amps exist. If this weren't true, we would all have a big solid state amp that uses 50db of GNFB to deliver .00nuthing THD!
A simple SE tube amp may have 1% THD that is predominantly second harmonic, and sounds great with simple music, but it may fall down on a complex piece with two dozen instruments and vocals.
That big SS amp mentioned above doesn't sound so vivid on simple vocal music, because the listener has grown accustomed to the 2nd harmonic distortion in his SE amp.
The happy medium lies somewhere in between these extremes, and many of us are still searching for it, or we wouldn't be here.
It depends a lot, but a blanket number, namely -100 dB has stood the test of time and subjective testing.
If one does bias-controlled testing of both static and dynamic distortion, one finds that static distortion is far more likely to be heard, simply because being static, it is always there to be heard.
That is true and true even to greater extremes. You mean that you never figured out how this affects the hand-wavey audiophile speculations about dynamic distortion?
All true, and it affects the dynamic distortion argument, but not in a good way.
If you don't know that an extremely high percentage of all amps used in audio fit this description, then you need to get out more!
In the cloister of enthusiast forums, the normal statistics of life are badly skewed. I think there are more than 1000 stores in my town that sell audio amps (for reproduction of music/EFX/dialog), and I can only think of one that stocks tubed gear. Trust me, its not the place with the highest volume, or even what most people would call a commercial volume of product going out the door.
Agreed, except you may be a little to kind to the poor, obsolete thing.
Solution: don't make a habit out of listening to inherently technically inferior gear. Then the vocals sound just fine. Its a discipline, just like not growing accustomed to speakers with peaky response.
Now you seem to be totally unrealistic about what most music lovers listen to.
Such statement comes from the assumption that DACs, preamps, amps, and cables have their own audible sound signature. Have you cited any evidence of that?
If you (or the author) measured the right parameters, the difference would have been known.
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Hey, I have built a dozen or so of the poor obsolete little things. Two of them get used a lot here.
Again, we could go on and on about how to define "music lovers." I knew people who indeed loved music but weren't too picky about how it was reproduced. They often had those funny little white things in their ears.
At it's peak the Motorola plant where I worked for 41 years had about 5000 people. About 1000 of them were engineers. At least 1/3 of them were electrical engineers. There were three of us who played with that obsolete technology for HiFi use, and a couple more that built tube guitar amps. I was the only one with a little tube amp in my office....until the safety Nazis banned it.
I used to say that to some of the people at work. Trust me a place with 1000 engineers, predominately male, with a median age of 27 is NOT a normal cross section of society in general. It is hard to explain that concept to a group of 50 people in a meeting discussing a new product.
I know, and have built and owned plenty of them. I still have a few high GNFB solid state amps. I still PREFER the sound produced by a high powered (100+ WPC) push pull tube amp with moderate feedback around as few stages as needed to adequately damp the speaker and reduce distortion.
I would say that I have a fairly 'educated' ear. I was very fortunate to have a music-loving mother who dragged me to symphonic concerts from a very young age. I used to hear a friend of my mother's, a wonderful cellist, practice regularly in our living room. I also lasted fifteen years as a jazz musician, during which time I got to hear a lot of great unamplified acoustic music, especially in rehearsals where there were no PA systems to muck up the sound.
I have never heard a playback system reproduce the true sound of an orchestral string section. Never. However, I have heard playback systems that play back recordings of orchestral string sections in a pleasing way.
I have heard many supposedly good playback systems reduce the sound of a lovely ride cymbal in a jazz drumkit to a wash of white noise. But if you've ever heard someone like Jimmy Cobb easing the sound out of a 1950's K. Zildjian ride, you know that a good cymbal played by a master drummer has a world of harmonic content to its sound.
Can someone propose a standard playback system that can be used as a standard of reference for an 'accurate' setup? Let's say we take a 24-bit/192kHz stereo, non-data compressed PCM audio file, played through a technically suitable DAC, with a technically suitable output stage. Now we play that through a volume control, amplifier and speakers.
What volume control, amplifier and speakers can we choose that will reproduce said PCM digital recording at an acceptable level of technical accuracy?
If that gets decided upon, I'd like to go out and listen to a system made of this kind of gear, and find out what I've been missing.
Is that possible?
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I have never heard a playback system reproduce the true sound of an orchestral string section. Never. However, I have heard playback systems that play back recordings of orchestral string sections in a pleasing way.
I have heard many supposedly good playback systems reduce the sound of a lovely ride cymbal in a jazz drumkit to a wash of white noise. But if you've ever heard someone like Jimmy Cobb easing the sound out of a 1950's K. Zildjian ride, you know that a good cymbal played by a master drummer has a world of harmonic content to its sound.
Can someone propose a standard playback system that can be used as a standard of reference for an 'accurate' setup? Let's say we take a 24-bit/192kHz stereo, non-data compressed PCM audio file, played through a technically suitable DAC, with a technically suitable output stage. Now we play that through a volume control, amplifier and speakers.
What volume control, amplifier and speakers can we choose that will reproduce said PCM digital recording at an acceptable level of technical accuracy?
If that gets decided upon, I'd like to go out and listen to a system made of this kind of gear, and find out what I've been missing.
Is that possible?
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I'm sure you've heard a system that sounds closer to the true sound than others. In hi-fi, that closer one would be considered better quality.
Yes. Presumably, it's recorded in a room. It has its own polar pattern which interacts with the room and the polar pattern of the mikes.
That implies that since I've never heard a system that comes close to reproducing the sound I experienced, that all I can hope for is the system that comes closest to reproducing the sound I experienced. That then suggests that all such systems distort the original sound, even the supposedly 'reference quality' super-'accurate' systems. So where does that leave me?
That leaves me choosing the system whose sound I like best for the music I listen to.
Unless there's a standard reference we can agree on that I should go hear so I can calibrate my expectations.
What surround system then? How many speakers are necessary? Is Atmos the minimum required, or is good ol' 5.1 sufficient? Are two or more subs an absolute necessity?SY said:
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Arny: What AV receiver from ca. 2005 would be a good amplifier for me to use as a reference? I have a Pioneer VSX-710S at my disposal. Is this a sufficiently good amplifier to use as a reference for comparison to other amps?
I have a DVD player with optical output that I can connect to the VSX-710S optical input. That way no analog line stages will come between source and amplifier. The resulting sound should be very good, then. The better the speaker, the better the sound, right?
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Even the best systems are a llooonnggg way from having any hope of that… current hifi is so bad (in absolute terms) that there are many ways to approach that ultimate goal. Even if we had the tech to capture it.
That does not mean that hifi is not a good entertainment medium.
dave
These are all actual interesting and as-yet unsolved questions in audio- unlike simple stuff like amplifiers or wires.
The most convincing I've ever heard was an Ambisonics system, but there's no readily available recordings in that format, it's a complete diy project. That said, it was (for me) an order of magnitude more realistic than anything else I've ever heard in reproduced sound.
Thanks for your solid feet on the ground post.
I also listen to a lot of live sound every day , I make guitar and bass amps for a living so every week I am at some rehearsal room or stage where at least the drums , percussion and brass/horns are live, plus an occassional acoustic or nylon string guitar heard from 3 feet away (even if amplified for the audience) .
Throw in some harp (harmonica) and the odd violin in the menu.
Even more, I walk among them rather than listening to the amplified version like audience does (remember I'm the old fat bearded guy with a credential hanging from his neck walking around onstage during sound tests)
What I hear there is never never ever ever reproduced, even "almost" , by *any* sound system on the Planet.
Just for one, think "soundstage" 😱
In a way, it's depressing to confirm, week after week for the last 45 years , how POOR is any kind of music equipment relative to a live performance.
The closest I have heard, so far, and that's an impressive achievement, is to listen in a darkened room to a *good* stereo-direct-to-recorder recording of a not too complex or loud sound source, think clasic piano, a Jazz trio, a couple singers plus a couple acoustic instruments, trough a good loud fast SS amp and very flat speakers.
There the illusion of having voice and instruments before you, as if heard through an acoustically transparent curtain and in their proper positions is quite realistic.
I've been accused of being "bitter" because I fail to believe replacing a $0.05 resistor for a $60 one can improve soundstage🙄
Those claiming so have NO CLUE about what soundstage is. Period.
Just do something similar to what I do regularly (you can go to a small club and sit at a front table, or listen to a symphonic orchestra or some Jazz .... LIVE) and then you will start to grasp what the word means.
I also try to go to our Teatro Colón, the Buenos Aires Opera House, at least twice a Year, and listen to any orchestra playing.
Close your eyes, relax, and you'll notice you have never ever listened to that on any system.
Don't trust me, just do it. 🙂
PS: almost forgot: what about tube amps?
In a nutshell, flawed as they are, SS amps are WAY (by orders of magnitude) flatter, cleaner, less distorted under any denomination, faster, less hummy/buzzy/hissy , in a word more *transparent* than anything tube driven.
That tubes might add some variations, and that such variations might be found agreeable by some, is not the point.
By the same token , I might look at some landscape through a window and might find it nicer through a pink, blue or green tinted glass, for some psychological reason, but a neutral flat transparent glass is way better in my opinion, definitely closer to no glass at all which would be the ideal.
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