Topic: 1% THD of Pioneer Receivers

[arthurallanj]

In all humility, thank you, Sir aHobbit.

[av_phile1]

Sir,

Maybe I'm wrong but I still haven't seen any manufacturer use white/pink noise as input signal injection when measuring THD. The only "real" way for them to measure a certain THD level at a full frequency spectrum (bandwidth) is to use a signal injector that contains the full freq. spectrum hence a white/pink noise must be used. But most of these measurements use an AF signal injector that has a variable frequency sweep, hence only one freq is selected at a time.

I don't mean any disrespect with you bro but for your post to be true (the one where you look for the %THD at full bandwidth), then the amp your looking for must publish either one of the following:

1. An amp with a fixed %THD from 20Hz-20Khz
2. An amp with %THD values taken at different frequencies.

Again, I don't mean any disrespect, just clarifying things.   Have fun bro! 

Sincerely,
JojoD

So what does the following THD spec often found in many reputable amps mean:

100watts continuous RMS into 8 Ohms,  20Hz to 20Khz, < 0.06% THD,  all channels driven. 

Is that THD valid for the quoted bandwidth?

THD/IM:  less than 0.05% at rated output into 8 ohms

What do you think is the frequency at which this rated output THD was measured?

[av_phile1]

I guess we all know that most amp manufacturers would find ways to impress potential buyers. And publishing specs like 500Watts at 10% THD is one way they could attract potential buyers that are less informed. So, again, I say pioneer hasn't violated any laws, it's just that for some who do understand those specs, nakakadismaya. There's that feeling that this certain brand is attempting to attract me into buying their product using tactics such as this. It's actually IGNORANCE that would get you deceived. Dati, I did not even care to look at THD's and Bandwidths, etc. on amp specs, but now I'm glad, with the help of Sir AV, I do. And now I understand. Point? I would always have more respect for a brand that publishes 100 WpC at 0.06% THD than the one who says 100 WpC at 1% THD. The latter would at least have my respect it if said, 75WpC at 0.06% THD. Again, Sir AV is just sharing some knowledge he firmly believes in, it's up to anybody to accept it or not. At least, with integrity, Sir AV will always have my respect. I see no point in arguing or proving somebody wrong. It's your brain, use it as you please.

Thanks Arthurallanj.  Glad to know someone's learning from what little I can share.  You're right, members here like you are intelligent enough and free to discern and accept or reject what they themselves think are right for them.  You only need to present your arguments well and dispassionately. 

And with regards brands that overhype they  products, like I said, they are shooting themselves in the foot.  They probably can get away with it, but they leave a bad taste in the mouth for those who know.  It's really a testament to commercialism that some famous brands already known for excellent makes would like to create the wrong impressions in order to get market leadership or dominance.  It's really up to the consumer to educate himself for a more informed decision in his purchases.   But I think that's really the name of the game in cutthroat mass commercialism.   

[JojoD818]

So what does the following THD spec often found in many reputable amps mean:

100watts continuous RMS into 8 Ohms,  20Hz to 20Khz, < 0.06% THD,  all channels driven. 

Is that THD valid for the quoted bandwidth?

THD/IM:  less than 0.05% at rated output into 8 ohms

What do you think is the frequency at which this rated output THD was measured?

Sorry av_phile1, but I think you already know the answer to your question or your just trying to prove me wrong.

I think you have actually tested a "real" amp and measured it's THD in real time right? And you wouldn't just rely on the factors printed at the back of the amp or the user's manual right?

Aside from the commercial amps that I have bought in my lifetime, I build some of my amps myself, and tested them myself too. In the case of my diy amps, I have to use quantitative analysis just to justify that the distortion factors are humanly acceptable and correlates with the calculated distortion factors.

I am just trying to help others by information, and I have no reason to prove myself to anyone. I believe in science, and it's language is math, I only use the paper to write the math and nothing more. I don't want to be the source of wrong information for that matter so I hereby rest my case.

Enjoy the music Gentlemen.

Jojo Dijamco

[aHobbit]

It's really up to the consumer to educate himself for a more informed decision in his purchases.   But I think that's really the name of the game in cutthroat mass commercialism.   

Right on, avphile1! Would say "properly" educate himself. When we talk about sound or music, it's not the eyes that should be the final arbiter, it should be your hearing senses!

Jojo is correct. Your information, that Pioneer is misleading the public, has no factual basis but your opinion.

When you say an amp measured in full audio spectrum and came out 100W at .06THD does not tell that the amp will perform good. The tale of the myriads of amps specs like frequency deviation in the audio range like 0,-3dB or the likes tells a lot of other story on the performance. And what you are telling these newbies, if they have to absorb what are all these specs at the back of manual, will just amount to nothing if they are really non-technical people. Even if they learned all of these technical jargon, will not guarantee them that they will end up with a gear that they really like (performance wise).

Some people have enjoyed the benefit of surplus amps not because they know the specs but because they audiioned them. The true audiophile does not really rely on paper specs - they listen.

You yourself tell them they misled people in their specs - and all consumer published their specs - and how do you know the rest of those adored product of yours did not misled the people?    You just look at them how they were built    , they were expensive  , you just listen to it based on your idea of sound  , based on the tell tales of others who have their own idea of sound as well  - but no way you measured it!   and you want these newbies depend on that paper.

Listen to it so you will not get caught in the many tricks of commercialism! 

And all commercial amps, expensive or not, popular or not, will try to hype or overhype. All of them aspire to be the number1. 

[av_phile1]

Sorry av_phile1, but I think you already know the answer to your question or your just trying to prove me wrong.

I think you have actually tested a "real" amp and measured it's THD in real time right? And you wouldn't just rely on the factors printed at the back of the amp or the user's manual right?

Aside from the commercial amps that I have bought in my lifetime, I build some of my amps myself, and tested them myself too. In the case of my diy amps, I have to use quantitative analysis just to justify that the distortion factors are humanly acceptable and correlates with the calculated distortion factors.

I am just trying to help others by information, and I have no reason to prove myself to anyone. I believe in science, and it's language is math, I only use the paper to write the math and nothing more. I don't want to be the source of wrong information for that matter so I hereby rest my case.

Enjoy the music Gentlemen.

Jojo Dijamco

I have my suspicions, that's why I'm asking. Defering to someone with fresher and  more recent experience than I have.  So I can get a confirmation on an aspect raised by what you said. 

It has been a long while since I've engaged in DIY over those Taiwan based amp kits to remember the actual lab measurements that went with them.  If I recall right. they were exhaustive, detailing the THDs at various frequency points within the audible spectra, just not so sure if they are 1 octave apart or something else.  They tabulate the RMS voltages at those frequency points and another at different speaker loads.  They even have IM graphs and frequency response graphs to illustrate the peaks and valleys and the db variations at at least 3  power levels. As well as the noise spectra.   You can really visually confirm if the amp is flat or not.  From these specs, you can almost corelate data with what you hear.

Hence, I am under the impression that those specs you nomally find in user manuals are watered-down SUMMARIES culled from such extensive lab tests or from the technical design specifications.  They are technically incomplete.  And therefore, may have little or no correlation with what you hear.   But their form, substance and language have been the de facto minimum literature conforming to FCC or whatever measurement standard the vendors prefer that should accompany any sound amplification device. 

So, if a summarized spec says 0.06% THD, 20Hz to 20khz, I would assume that that is a nominal value that the consumer can reasonably expect at ALL the frequencies in that bandwidth.  Right? 

 

[JojoD818]

So, if a summarized spec says 0.06% THD, 20Hz to 20khz, I would assume that that is a nominal value that the consumer can reasonably expect at ALL the frequencies in that bandwidth.  Right? 

 

My thoughts only:

1. If the manufacturer is telling the truth then my answer is yes.
2. If it has been measured by an independent entity/lab then again yes.

But then again, it can be an average THD measurement which is again, misleading. You yourself experienced measuring THD in you dir days, you may have noticed that THD increases as freq increases, so a THD measurement must be accompanied by a freq where it was taken.

An average THD on a bandwidth of 20Hz-20KHz can be very irritating for people who understand how this are measured, right? It can be 0.001% at 100Hz and 0.1% at 20Khz, when we average these numbers we get a smaller THD at higher frequencies but yes, it is a reading from 100Hz-20Khz then.

You see, this things cannot be summarized in a couple of paragraphs, we haven't even touched the other parameters of amplifiers that greatly affects THD, IMD, S/N ratio, etc.

Cheers!

[av_phile1]

I could be wrong, but my understanding about THD is that they are a mathematical summation of all the unwanted harmonics generated where there shouldn't be as per the source material.  Hence, lower frequencies tend to produce more audible high order harmonics than at higher frequencies.

Those THD specs rated over a bandwidth may be incomplete, but if you notice in many reputable amps and receivers like NAD, HK and Musical Fidelity, the THD figures given are the highest over the 20khz bandwidth, like <0.06% THD. There's a ("<" )less than sign before it, meaning the number given is the highest over that range at the RMS point where the measurement is taken.   Others use the 1kz point which have more audible harmonic multiples than at 10khz.

[JojoD818]

Your understanding of commercial amps specs is correct, but not with the understanding of THD.

THD tends to increase with frequency, meaning as the frequency increases, the THD also increases.

Now please sir, let's not include order of harmonic distortions in these thread because it would include tube amps as well as solid state amps when order of distortion is studied.

I don't want to sound techie or be called a techno freak by our friends here but it may seem that some of them cannot already follow what we are talking about let alone discuss order of harmonic distortions that would include an amps damping factor, linearity, slew rate, noise floor, s/n ratio, IM, and other unheard terminologies that would only be for the benifit of the two of us. 


Regards,
JojoD

[jerix]

I don't want to sound techie or be called a techno freak by our friends here but it may seem that some of them cannot already follow what we are talking about let alone discuss order of harmonic distortions that would include an amps damping factor, linearity, slew rate, noise floor, s/n ratio, IM, and other unheard terminologies that would only be for the benifit of the two of us. 


Regards,
JojoD

bros, your discussion can help us somehow-- just allow us to ask questions from time to time -- cheers!

[aHobbit]

bros, your discussion can help us somehow-- just allow us to ask questions from time to time -- cheers!

huhulaan ko ending ng discussion ni avphile1 at JojoD 

We will all learn the specs of amps and determine in what way it affects the amp performance.   

Then when we buy amp, we will just listen with our ears, because our heads will be so dizzy already with those techie things   

Merry Christmas!

[5Speed]

ahobbit... nahihilo na nga ako kababasa eh...hehehehe

 

makapakinig na lang muna nang musik....
 

[arthurallanj]

Ever heard of the expression "growing pains"? That's because growth is painful... He he he Peace! mga bro.

[JojoD818]

huhulaan ko ending ng discussion ni avphile1 at JojoD 

We will all learn the specs of amps and determine in what way it affects the amp performance.   

Then when we buy amp, we will just listen with our ears, because our heads will be so dizzy already with those techie things   

Merry Christmas!

Geez, I just hope that we learn new things in this thread! It is my intention to inform as accurately (not just in paper) and as down to earth as possible so everyone can benefit.

You are quite right, when I buy an amp, I listen first before I read the manual. 

Merry Christmas to all!

[jerix]

Do you guys look at what frequency this THD is measured on? If not, then you should, because harmonic distortions tend to increase as frequency increases and vice-versa.

Just want to supply what is being asked here. For this particular pioneer receiver, the manual indicates these values:--- 

Continuous Power Output (stereo mode)
frnt ------- 100w + 100w (DIN 1 khz. THD 1%. 8Ohms)

Continuous Power Output (surround Mode)
frnt ------- 100w/ch (1khz, THD 1% 8ohms)
cntr ------- 100w/ch (1khz, THD 1% 8ohms)
srrnd------ 100w/ch (1khz, THD 1% 8ohms)
srrnd bk-- 100w/ch (1khz, THD 1% 8ohms)

Maximum Power(1khz, 10% RMS, per channel driven)
------------------------------------ 120w x 5
 

[JojoD818]

See? The measurements were taken at 1KHz which means that a sine wave signal injector set at 1000 cycles (Hz) was used as input signal. Now if the injectors center frequency would be sweeped higher then those  THDs will surely be higher for that particular power and vice-versa.

Although some manufacturers give a spec with a "20Hz-20Khz" range, Pioneer's specs would have been lower if they used this technique (20HZ-20KHz) because it averages the THD levels over the whole frequency spectrum.

Cheers!

[jerix]

See? The measurements were taken at 1KHz which means that a sine wave signal injector set at 1000 cycles (Hz) was used as input signal. Now if the injectors center frequency would be sweeped higher then those  THDs will surely be higher for that particular power and vice-versa.

Although some manufacturers give a spec with a "20Hz-20Khz" range, Pioneer's specs would have been lower if they used this technique (20HZ-20KHz) because it averages the THD levels over the whole frequency spectrum.

Cheers!

mastah jojo --- does it mean that under the 1khz measurement or condition all the other brands like the NAD, MF the onkyos, etc. may possibly register the same result to that of the pioneer's 1% THD?--  thnks !

 

[JojoD818]

Jerix,

This is my opinion only but I think others will agree with this:

With all test parameters being equal, i mean really equal (same test freq, load, etc.), your mentioned branded amps would definitely show lower THD at lower frequencies and higher THD at higher frequencies.

So what the heck does this mean to a person not interested in techno blah3?

This means that it is not FAIR to compare a Pioneer amp with a THD measured at 1KHz to an amp who's THD merasurements  are an average of the audio frequency spectrum (20Hz-20KHz).

This also means that if only the guys at Pioneer used the averaging technique in measuring their amps THD specs then they wouldn't be arriving at a 1% value.

If they just did that then none of these arguments will ever have been brought up. 

But HONESTY on their part is what makes a difference doesnt it? Even if makes rise to questions such as the title of this thread.

Cheers!

[av_phile1]

See? The measurements were taken at 1KHz which means that a sine wave signal injector set at 1000 cycles (Hz) was used as input signal. Now if the injectors center frequency would be sweeped higher then those  THDs will surely be higher for that particular power and vice-versa.

Although some manufacturers give a spec with a "20Hz-20Khz" range, Pioneer's specs would have been lower if they used this technique (20HZ-20KHz) because it averages the THD levels over the whole frequency spectrum.

Cheers!

I am a bit confused with what you said.  You said the higher the frequencies injected, the higher the THDs. So if they had used various injected frequencies across the entire spectrum, how sure are you that they'd get lower THD when averaged as opposed to getting it only at one frequency.  You have only 980 frequency points below 1khz with lower THDs, and around 19,000 frequency points above 1khz with higher THDs.  Now if they use 1 octave intervals after 20hz, maybe, since there's one more octave below 1khz than above.  Even then, taht depends on how much greater the THDs above 1khz are compared to how much lower the THD's are below 1khz.

But that may be beside the point.   THD is not averaged.  See those amps with the "<" sign before the THD figure, the THD over the entire 20khz bandwidth is not an average figure, but the HIGHEST obtained.  That's why they specify "<0.06%, 20hz - 20Khz,  so you don't expect the THD to be any higher at that power level at any point across the audible spectrum.

But, here I go again, if you want to hype your specs, you can always average it.  In the case of those specs given by jerrix,  the THD is measured ONLY at the 1Khz point.  Not averaged.  It can be MORE at higher frequencies. Hence, while other conservatively rated euipment will tell you not to expect any higher THD reading on their specs, the pioneer specs opens up the possiblity you can get higher THDs above 1k.

And not only is the 1 khz point a measurement condition that can yield a higher power rating vis-a-vis a full 20hz-20khz measurement condition, but the fact that the measurement is done with only two channesl driven (steeo mode. I assume both channels driven) is already a right step in the overhyping direction for a multichannel receiver.  Compare that to the specs of a conservatively rated ROTEL RSX1067:

100 watts/ch (20-20k Hz, <0.05% THD, 8 ohms)
(Seven Channel Driven)

(taken from the rotel site)

The measurement is made across the entire BANDWIDTH with ALL channels driven.  And the THD you should expect across that bandwith is less that 0.05%. Not more, but less. Not averaged. 

I have other caveat against power measurements done at 1khz instead of full bandwidth or with only one or two channels driven in a multichannel receiver.  But that's already out of topic.

[av_phile1]

Jerix,


This means that it is not FAIR to compare a Pioneer amp with a THD measured at 1KHz to an amp who's THD merasurements  are an average of the audio frequency spectrum (20Hz-20KHz).

Bingo.  IT IS UNFAIR.  But the unfairness is made at the expense of the consumer who may think he is comparing apples to apples - a 100wpc Pioneer versus a 100wpc NAD.  And it is equality unfair to the brand as well, as their slant towards power rating, at the expense of the other feartures in order to bring out the MOST numbers in the power game, is shooting themselves at the foot. 

[av_phile1]

Your understanding of commercial amps specs is correct, but not with the understanding of THD.

THD tends to increase with frequency, meaning as the frequency increases, the THD also increases.

Well, I could be wrong about THD's not increasing with frequency.  They probably do.  I'd leave it at that.

But I will stand pat on my understanding of THD as the summation of all unwanted harmonics generated by a fundamental frequency that is a byproduct of any electronic amplification device, whether tubes or SS.  THD is TOTAL Harmonic Distortion.  If TOTAL doesn't mean summation, what is. 

[JojoD818]

I am a bit confused with what you said.  You said the higher the frequencies injected, the higher the THDs. So if they had used various injected frequencies across the entire spectrum, how sure are you that they'd get lower THD when averaged as opposed to getting it only at one frequency.  You have only 980 frequency points below 1khz with lower THDs, and around 19,000 frequency points above 1khz with higher THDs.  Now if they use 1 octave intervals after 20hz, maybe, since there's one more octave below 1khz than above.  Even then, taht depends on how much greater the THDs above 1khz are compared to how much lower the THD's are below 1khz.

But that may be beside the point.   THD is not averaged.  See those amps with the "<" sign before the THD figure, the THD over the entire 20khz bandwidth is not an average figure, but the HIGHEST obtained.  That's why they specify "<0.06%, 20hz - 20Khz,  so you don't expect the THD to be any higher at that power level at any point across the audible spectrum.

But, here I go again, if you want to hype your specs, you can always average it.  In the case of those specs given by jerrix,  the THD is measured ONLY at the 1Khz point.  Not averaged.  It can be MORE at higher frequencies. Hence, while other conservatively rated euipment will tell you not to expect any higher THD reading on their specs, the pioneer specs opens up the possiblity you can get higher THDs above 1k.

And not only is the 1 khz point a measurement condition that can yield a higher power rating vis-a-vis a full 20hz-20khz measurement condition, but the fact that the measurement is done with only two channesl driven (steeo mode. I assume both channels driven) is already a right step in the overhyping direction for a multichannel receiver.  Compare that to the specs of a conservatively rated ROTEL RSX1067:

100 watts/ch (20-20k Hz, <0.05% THD, 8 ohms)
(Seven Channel Driven)

(taken from the rotel site)

The measurement is made across the entire BANDWIDTH with ALL channels driven.  And the THD you should expect across that bandwith is less that 0.05%. Not more, but less. Not averaged. 

I have other caveat against power measurements done at 1khz instead of full bandwidth or with only one or two channels driven in a multichannel receiver.  But that's already out of topic.

I was surprised it took you so long to post your comments. 

"I am a bit confused with what you said.  You said the higher the frequencies injected, the higher the THDs. So if they had used various injected frequencies across the entire spectrum, how sure are you that they'd get lower THD when averaged as opposed to getting it only at one frequency.  You have only 980 frequency points below 1khz with lower THDs, and around 19,000 frequency points above 1khz with higher THDs.  Now if they use 1 octave intervals after 20hz, maybe, since there's one more octave below 1khz than above.  Even then, taht depends on how much greater the THDs above 1khz are compared to how much lower the THD's are below 1khz."

You don't have to believe me nor anyone else in this forum. How sure am I? I'm very sure. 

"The measurement is made across the entire BANDWIDTH with ALL channels driven.  And the THD you should expect across that bandwith is less that 0.05%. Not more, but less. Not averaged. "

So does this mean this is the highest %THD? If it is, then that amp is a very good amp indeed. If the tests were done by an independent institution and not by the manufacturer then by all means I'll believe it.

[JojoD818]

Well, I could be wrong about THD's not increasing with frequency.  They probably do.  I'd leave it at that.

But I will stand pat on my understanding of THD as the summation of all unwanted harmonics generated by a fundamental frequency that is a byproduct of any electronic amplification device, whether tubes or SS.  THD is TOTAL Harmonic Distortion.  If TOTAL doesn't mean summation, what is. 

"Well, I could be wrong about THD's not increasing with frequency.  They probably do.  I'd leave it at that."

Nice way of putting it, but for me, I don't leave it at that as you do, I'd rather accept it for it is what it is.

"But I will stand pat on my understanding of THD as the summation of all unwanted harmonics generated by a fundamental frequency that is a byproduct of any electronic amplification device, whether tubes or SS.  THD is TOTAL Harmonic Distortion.  If TOTAL doesn't mean summation, what is. "

THD is a summation, a total of the different orders of harmonic distortions, be it odd or even harmonics. Oh yes, you are right, just don't include crossover distortion and inter-modulation distortion in your summation.

[av_phile1]

THD is a summation, a total of the different orders of harmonic distortions, be it odd or even harmonics. Oh yes, you are right, just don't include crossover distortion and inter-modulation distortion in your summation.

Ofcourse,  they're an entirely different set.  Though IM results from the intermodulation among harmonics that is distortion as well.

[JojoD818]

Ofcourse,  they're an entirely different set.  Though IM results from the intermodulation among harmonics that is distortion as well.

Just clarifying......

IM is not a result of inter-modulating harmonics, but yes it is also distortion.

INTER-MODULATION (or sometimes TIM for transient intermodulation distortion) occurs when an input signal overloads the input stage of an amplifier, causing it to either cut off or to become nonlinear for an instant before the feedback signal arrives (feedback correction). If the input stage cuts off, the amplifier output slews and the amplifier produces hard IM distortion. If the input stage becomes nonlinear but does not cut off, the amplifier is said to exhibit soft IM distortion.

THD is the sum of odd & even harmonics yes, but IM is a differrent orange in the world of amps.

Regards,
JojoD

[av_phile1]

Just clarifying......

IM is not a result of inter-modulating harmonics, but yes it is also distortion.

INTER-MODULATION (or sometimes TIM for transient intermodulation distortion) occurs when an input signal overloads the input stage of an amplifier, causing it to either cut off or to become nonlinear for an instant before the feedback signal arrives (feedback correction). If the input stage cuts off, the amplifier output slews and the amplifier produces hard IM distortion. If the input stage becomes nonlinear but does not cut off, the amplifier is said to exhibit soft IM distortion.

THD is the sum of odd & even harmonics yes, but IM is a differrent orange in the world of amps.

Regards,
JojoD

Well, I hope you're not confusing the meanings of Transient Intermodulation Distortion and plain Intemodulation Distortion that I was talking about.  As far as I can recall, these two are different distortion products but share the same intermodulating action.  What I am saying is that IM is the result, more specifically, the sum and difference of various frequencies that arise when unwanted harmonics appear at the point of clipping.  Whenever there are at least two frequencies on the same path, they intermodulate with one another to produce new frequencies that were not there at the input stage.  And anything added to or subtracted from the original signal is distortion.  When unwanted harmonics are generated as the signal is amplified, those added harmonics that you add to get those THDs produce unwanted intermodulation products called IM  that can be more objectionable than plain THDs.   I think both THD and IM are classifed as harmonic non-linear  distortions. 

OTH Transient Intermoducation Distortion is classified as time-based and non-harmonic.   But just to distinguish with plain or static IM,  TIM results from the application of global or local negative feedback designs aimed at reducing THDs but add transient instantaenous dynamic distorton products called TIMs.   I have no material quarrel with your definition of TIMs.  Those transients do overload the input stage of an amp until the feedback signal arrives.  But often phase-shifted or delayed, thus producing new trransient frequencies that intermodulate with each other.  That I think is why TIMs are time-based distortion products.  Again as the term suggests, there is intermodulation action between frequencies, but among transient signals - the most audibly severe among distortion  products.
 
Now that's what I recall from my early days in the hobby. As usual feel free to correct me.  There may be some newer definitions i am not be aware of from new design applications.  But that's where you come in.   

[jerix]

'OLALA!!---I now feel that m inside the amp--tryin to figure what is causing what 

[arthurallanj]

Medyo nakakahilo na nga bro jerix ano? But ganyan talaga when you search for knowledge, medyo masakit...... sa ulo. When we strive to grow, pain is always the result. Again, Growing Pains nga, di ba? I'm just an observer here hoping na maambunan naman ako ng katalinuhan ng mga taong ito. Thanks, mga bro.

[av_phile1]

So does this mean this is the highest %THD? If it is, then that amp is a very good amp indeed. If the tests were done by an independent institution and not by the manufacturer then by all means I'll believe it.

No it's not.  The THD was measured at 1khz.  So by your own explanation that there are more THDs in the upper frequencies, an amp that publishes its THD  only at 1khz has MORE THDs waiting in the upper regions.  Compare such a measurement to the ROTEL that gives the MAX %THD across the entire audible bandwidth.  And whether that was measured by an independent lab or the manufacturer doesn't change the fact that it is a published specification made availalbe at the sales floor for consumers.

[JojoD818]

I wouldn't be correcting you anymore because knowing is far from understanding. I just hope that your belief or shall I say knowledge of audio power amplifiers is as accurate so that others can benefit from your informative posts.

Have a nice one,
JojoD