Amplifiers bench tests results-should we care or not, regardless of audibility, are those thresholds such as -100, -80, -40 dB THD+N, IMD etc.useful?

Are bench test results useful for decision making regardless?

  • Only if the results are all too close to or exceed thresholds of audibility

  • No, well designed amplifiers have flat response 20-20 kHz and THD+N below -60 dB (worst conditions)

  • Yes, because not all of the thresholds of audibility for various measurements are known


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Trell

Trell

Audioholic Spartan
Factually speaking, no! Based on hearsay, many took his commentary out of context, yes!! Some forum posts might have made you believe that all ASR cares about is SINAD, the rest is history. Such kind of talks got repeated enough, so many people believe it is a fact that ASR/Amir cares only about SINAD of the preamp/dac, but that is not true.
...
Thanks for yet again posting a very thoughtful and detailed reply to the same question(s) from the same poster(s) you have answered several times in this thread already! I must admit you are much more patient than I am.
 
P

PENG

Audioholic Slumlord
Thanks for yet again posting a very thoughtful and detailed reply to the same question(s) from the same poster(s) you have answered several times in this thread already! I must admit you are much more patient than I am.
Thank you for the kind words. ADTG and I know each other electronically for many years, so we know how to deal with each other on this forum.:)
 
AcuDefTechGuy

AcuDefTechGuy

Audioholic Jedi
Factually speaking, no! Based on hearsay, many took his commentary out of context, yes!! Some forum posts might have made you believe that all ASR cares about is SINAD, the rest is history. Such kind of talks got repeated enough, so many people believe it is a fact that ASR/Amir cares only about SINAD of the preamp/dac, but that is not true.



Let's quote exactly his own words in the conclusion of his review on the Denon first, and then compare some of the measurements:
Denon AVR-X3800H Review | Audio Science Review (ASR) Forum



My interpretation is that as you said, it at least has a lot to do with the DAC, but don't you think in this case it is understandable, considering the SINAD spec of the DAC chip dropped from 107 dB (best case) to 93 dB (best case)? Okay we agreed many times in the pass that 93 dB SINAD is not an audible issue, but even if this is true under any conditions, would you be disappointed if you found out you next CX-A5300 got the DAC chips downgraded to the one D+M are now using, so the SINAD spec, or THD+N spec dropped from your CX-A5100's -110 dB to -93 dB, a whopping 17 dB increase in THD+N, and the price had gone up by 50% to offset inflation?



I have agreed with you in the past that THD+N of 0.01% is fine , even 0.05% is fine if it is the worst case scenario but you can't say the same by looking at a single measurement point such as the typical 1 kHz test, and without specifying the frequency bandwidth and output level.

With that in mind, please compare the following, that I have also posted using ASR's measurements as example. You can used Gene's too, but it is easier to find Amir's simply because he has done so many.

View attachment 59744

View attachment 59745

I remember you suggested that we should look at SNR in conjunction with THD+N so now let's compare their SNR:

See that the Rotel is at least 10 dB better, and by the way, the example RX-V377 you cited showed very good SNR but S&V did not specify the output level, so it could be (most likely) measured at rated output, and their figures were almost always "A weighting", ASR's are for 22.5 kHz bandwidth, unweighted.

Cautionary note: Here we are comparing SNR measured on an AVR versus that measured on a power amp, I don't what the SNR would be if the AVR's power amp itself was measured.

View attachment 59746

View attachment 59747

So to me, the takeaway of his reviews, it you always read the entirety, would be the following:

- ASR typically provide many charts, the first one is the SINAD ranking, may be because that is usually the first of a battery of tests, and also because he does think the preamp/dac section is important as many ASR members use external power amps that could have gains from as low as under 20 dB to as high as over 30 dB.

- ASR does not look at SINAD as a single number, just because their is a ranking chart, making it easy to compare, and index the large number of reviews for easy find, does not mean that is the only metric to look at. Members who frequent the site, usually know well enough to look through the rest of the reviews before making their jumping to decision.

- When looking at SINAD, one should look carefully on the graphs if provided, again, the single point one measured with a 1 kHz signal is only for a quick compare, and if it is >>100 dB that may be good enough, but if it is lower, such as <90 dB, go look for the details, as that may tell you a different story.

- It is not true that Amir's recommendations are based on a single SINAD number. The Rotel example shows that he does consider other metrics, even the price point is often considered, remember his comments on those $20, or was it $12 dongle dacs? I picked the Rotel as example because it's the latest review, readily available. You can find many more examples that shows what some of those youtubers said about the site's is not always true, though in some cases may be true to a point. Remember that Youthman vido that got posted and reposted, sometimes that's how hearsay became hearsay, as those guys have the megaphones that you and I don't have.

Lastly, back to your first question, I can think of a few AVRs/AVPs that have excellent DAC chips that did not get on Amir's recommended list.

Arcam AVR/AVPs - Arcam typically used better DAC chips than the mass producers such as D+M's, and Amir has reviewed at least 3 or 4 of their AVRs and AVPs, none got his recommendations.

Anthem AVRs also typically used above average DAC chips (for AVRs) and out of the 4 AVRs/AVPs, only 2 made it to his recommended list.

Marantz AVR/AVPs - He reviewed quite a few, recommended none, even the $5,000 AV8805 that has AKM's ex flagship DAC did not make it, but almost, if you read the fine print that he sort of said ..buy it for the feature..
Thanks.

1. SNR. So the Rotel amp does have better SNR than the X3800 (worst case is 99dB vs 90dB).

2. THD+N. And although the x3800 THD+N is better than the Rotel at 1kHz, the Rotel’s THD+N is better from 5-20kHz, especially above 10W? Should we care about the measurements above 5W?

Does it work if we averaged the SINAD from 20Hz-15kHz? But then at what power output, 1W, 5W, 10W, 20W? Or average the SINAD from 20Hz-15kHz and from 1W-20W?
 
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AcuDefTechGuy

AcuDefTechGuy

Audioholic Jedi
ADTG and I know each other electronically for many years, so we know how to deal with each other on this forum.:)
From one long time career professional to another long time career professional. :D
 
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P

PENG

Audioholic Slumlord
Thanks.

1. SNR. So the Rotel amp does have better SNR than the X3800 (worst case is 99dB vs 90dB).
I am not sure if the difference is that much because while both were measured at the speaker outputs, one is an AVR and the other is a power amp. I would think the accumulated noise in the AVR case might be a few dB (2, 3 dB or less?) higher due to the preamp's noise contribution. I tried calculated it before but too lazy to do it now, but I remember it would not be much. May be @gene can show us, or he might be able to give us a approx/rule of thumb number when comparing SNR of an AVR vs power amp at the 1 W/2.83 V output level.

2. THD+N. And although the x3800 THD+N is better than the Rotel at 1kHz, the Rotel’s THD+N is better from 5-20kHz, especially above 10W? Should we care about the measurements above 5W?

Does it work if we averaged the SINAD from 20Hz-15kHz? But then at what power output, 1W, 5W, 10W, 20W? Or average the SINAD from 20Hz-15kHz and from 1W-20W?
It depends, if you ask people like Dr. Geddes, he might say as low as possible, even 0.001W because 1W is a lot of SPL, you may also get similar answer from Nelson Pass, and John Siau as those are the proponents of the importance of the first watt distortions.

As I understood it, the reason why it would be great to see THD (not THD+N) measured at well below 1 W is that it would give indication of the distortions contributed by crossover distortion specifically. Unfortunately it is very difficult to measure THD especially at the very low output level.

In my opinion, though, and thinking strictly as an engineer I would say those PhDs, while correct in theory, might have a) exaggerate to make their point that few people had made, and b) relied on the older technology. On b), the last time I saw gedlee (Dr. Geddes) posted on the topic was almost 20 years ago, at that time how many people used the APs that Gene and Amir regularly to measure THD, and which model of AP was JA using?

Having said that, I don't think we can discount the importance of measuring crossover distortion (but good luck finding such measurements published), or at least measure THD down to the lowest possible level so as to get an idea. For example, I do prefer the Rotel's distortion curves much more because they showed almost no dependency on frequency and output level, so there is a good chance that it would remain low at well below 1 W, even 1 mW, indicating very little crossover distortions to worry about.

One thing I gather is, speakers that have lower sensitivity may not be all bad, for example:

86 dB/2.83V/1m - At 2 meters, you get 80 dB, so assuming 8 ohm nominal, the amp will output 1W, and if you listen to 60 dB spl average, the amp will still have to output 0.01W, that is 10 mW. At 10 mW output, the Rotel amp's THD would likely be still below 0.05% if your extend the trend line on that graph.

So I think using the so call difficult to drive speakers might actually be better as long as you have powerful enough amps to drive them, as you will be less likely be subjected to the allegedly most offensive type of non linear distortions, namely the crossover distortions.

Amplifier Crossover Distortion - Benchmark Media Systems

Is 0.05%, assuming all contributed by the crossover distortion, audible? I suppose it could be, but I doubt it would be audible to the point that it would cause fatigue as such. If it is 0.1%, and mostly make up of crossover distortion, then I think most experts will consider that not acceptable.
 
Trell

Trell

Audioholic Spartan
To some of the posters in this thread take a look in the following review on ASR and the comments to Amir's review/measurements.

Hint: It's not all about SINAD.

 
panteragstk

panteragstk

Audioholic Warlord
To some of the posters in this thread take a look in the following review on ASR and the comments to Amir's review/measurements.

Hint: It's not all about SINAD.

I like this statement.

Per above, I don't feel fully qualified to make a recommendation one way or the other.
 
P

PENG

Audioholic Slumlord
I should have included links to the technical articles by Mark Sanpilifo:

Human Hearing: Amplitude Sensitivity Part 1 | Audioholics

It is a 4-part article, probably the most comprehensive, yet relatively easy to understand article that I have been able to find on the internet. He covered amplitude, phase, harmonic distortions, intermodulation distortions and how we hear, 4 of the probably most important aspects when it comes to audibility thresholds. There are other well know physicists/engineers type such as gedlee, who have written a few on the topic, but those probably are more for physicists/EEs who have knowledge of advanced theory in the field of EE and mathematics.

I did not search through the 7 pages, so if it has been posted before, sorry about the duplicate, though it may help to include in again in case someone stumble on the thread and happen to read in reverse order.
 
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D

dlaloum

Full Audioholic
I should have included links to the technical articles by Mark Sanpilifo:

Human Hearing: Amplitude Sensitivity Part 1 | Audioholics

It is a 4-part article, probably the most comprehensive, yet relatively easy to understand article that I have been able to find on the internet. He covered amplitude, phase, harmonic distortions, intermodulation distortions and how we hear, 4 of the probably most important aspects when it comes to audibility thresholds. There are other well know physicists/engineers type such as gedlee, who have written a few on the topic, but those probably are more for physicists/EEs who have knowledge of advanced theory in the field of EE and mathematics.

I did not search through the 7 pages, so if it has been posted before, sorry about the duplicate, though it may help to include in again in case someone stumble on the thread and happen to read in reverse order.
It also points out the difference in audibility threshold under differing test regimes... with one test the threshold was circa 1db, with a different test it was 0.25db.

I've noticed that variations of around the 0.25db level (or possibly less) - in many circumstances do NOT result in a realisation that something is louder (or quieter) but rather tend to skew the impression of other aspects of the listening experience... it seems "clearer", imaging is more pronounced, certain instruments become more obvious in the mix, etc...

So depending on the test regime, and whether it targets "difference" or "loudness" - may pick something up, or not!
 
P

PENG

Audioholic Slumlord
This inteview of Earl Geddes covers a lot of relevant ground in terms of what is and isn't audible, and what the thresholds are....

Chat with Dr. Earl Geddes of GedLee Audio (youtube.com)
He basically said there was no threshold and explained why..., and it's much more about speakers.

Dr. Geddes, like Dr. Olive and Dr. Toole don't seem to talk a lot about amplifier distortions. One can see why that is the case, loudspeakers have much high non linear distortions so why worry about amplifiers so much. It is really hilarious when we keep reading people claiming how one amps sounded nigh and day better than another, even between virtually identical Denon and Marantz twins, and even funnier when you read about what they claimed about exotic opamps and cables.

No matter how much such informative video we post and people read, they got fixated in what they perceived that is heavily influenced by manufacturers marketing information, and to certain extent how well build the devices are, and that would include speakers too. When you look at some of those >$20,000 speakers your mind will likely be preconditioned.

The take away from those kind of videos is that, focus should really be on speakers and rooms, in order to understand how and why people can hear different sound quality from the devices in their room. Not saying amps all sound the same, they don't, but there is always a curve of diminishing return, and that curve for amps and loudspeakers must be very different, truly night and day different lol..

I watch that video at least a couple times before, nothing new, but it is still good to watch it once in a while. It is especially good for those who are open minded, but to those who don't believe in the power of Placebo effects, it would be a waste of their time and they might not even click on such links, if they got the sense that they wouldn't hear what they wanted to hear/believe.
 
highfigh

highfigh

Seriously, I have no life.
It also points out the difference in audibility threshold under differing test regimes... with one test the threshold was circa 1db, with a different test it was 0.25db.

I've noticed that variations of around the 0.25db level (or possibly less) - in many circumstances do NOT result in a realisation that something is louder (or quieter) but rather tend to skew the impression of other aspects of the listening experience... it seems "clearer", imaging is more pronounced, certain instruments become more obvious in the mix, etc...

So depending on the test regime, and whether it targets "difference" or "loudness" - may pick something up, or not!
The stated minimum noticeable difference in SPL has been 1dB, for decades and that was under controlled conditions- hearing .25dB in a reverberant space is unliklely.

A good source for this info is in F.Alton Everest's book Master Handbook of Acoustics- it covers human hearing, treatments, measurement, etc.
 
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