I am new in audiophile, so excuse me if I offend anyone here. I am not trying to stir up trouble. I always though tube gives even harmonics that is more pleasing to the ears. BUT, I read quite a few posts here. Sounds like the main thing about sound quality is low distortion. Both here and SS forum here are saying the same thing, the lower the distortion, the better the transparency and bigger the sound stage. So I just look at the two approaches and here is my opinions:
1) By the nature of tubes that you only have equivalent of NPN or NMOSFET, it is already a clean disadvantage to SS design that they have complementary devices like PNP or PMOSFET. Lots of advantage to be have for cancelling distortion using complementary devices cannot be done with tubes.
2) Then tube circuit has to have OPT, one more source of distortion and reduce open loop gain because it is stepping down. Lower loop gain implies more distortion.
3) Then it is so much easier to get higher gain for SS stage. Gain of the tube is limited, triode has internal plate resistance that limit the gain. In feedback circuit, the higher the loop gain( not open loop gain), the lower the distortion. You can't get enough gain with 3 tube stages particularly the OT is going to reduce the voltage to lower the output impedance. Again, lower loop gain implies higher distortion.
4) The output impedance of SS circuit with emitter follower or source follower is going to much lower than any tube amp output either through OPT or even no OPT. The speaker load is going to affect the amp. This with the fact the tube amp has lower loop gain, You can't get the output impedance low enough!!!
4) Also, most tube circuit is much higher impedance and bigger in size, this make layout much more critical and much harder to avoid crosstalk. In guitar amp, at least you only deal with 5KHz. Here you deal with 20KHz and the amp needs to be able to go much higher frequency response. Layout and wire length is going to that much more critical. I am reading the Audio power amp book by Bob Cordell, he is talking about the amps are design to have 500KHz BW. This is going to be a whole lot tougher for tube amp to run good at that frequency.
If tube distortion is not helping the sound of the tube power amp, I just don't see how tube circuit can be better than SS amp in respect of distortion performance.
Please correct me if I am wrong in any of the points.
Thanks
1) By the nature of tubes that you only have equivalent of NPN or NMOSFET, it is already a clean disadvantage to SS design that they have complementary devices like PNP or PMOSFET. Lots of advantage to be have for cancelling distortion using complementary devices cannot be done with tubes.
2) Then tube circuit has to have OPT, one more source of distortion and reduce open loop gain because it is stepping down. Lower loop gain implies more distortion.
3) Then it is so much easier to get higher gain for SS stage. Gain of the tube is limited, triode has internal plate resistance that limit the gain. In feedback circuit, the higher the loop gain( not open loop gain), the lower the distortion. You can't get enough gain with 3 tube stages particularly the OT is going to reduce the voltage to lower the output impedance. Again, lower loop gain implies higher distortion.
4) The output impedance of SS circuit with emitter follower or source follower is going to much lower than any tube amp output either through OPT or even no OPT. The speaker load is going to affect the amp. This with the fact the tube amp has lower loop gain, You can't get the output impedance low enough!!!
4) Also, most tube circuit is much higher impedance and bigger in size, this make layout much more critical and much harder to avoid crosstalk. In guitar amp, at least you only deal with 5KHz. Here you deal with 20KHz and the amp needs to be able to go much higher frequency response. Layout and wire length is going to that much more critical. I am reading the Audio power amp book by Bob Cordell, he is talking about the amps are design to have 500KHz BW. This is going to be a whole lot tougher for tube amp to run good at that frequency.
If tube distortion is not helping the sound of the tube power amp, I just don't see how tube circuit can be better than SS amp in respect of distortion performance.
Please correct me if I am wrong in any of the points.
Thanks
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The right kind and amount of Harmonic distortion adds a "warmth" or "musicality" to the signal which some find preferable, so low distortion is not necessary for a good 3 dimensional playback system, also speakers and room have a lot to do with the outcome. Tubes can be very linear and can produce very low distortion, it's the inefficiency (heater current), size, and cost that solid state wins at, and this is why the tube has been somewhat defeated. Also layout and design is less important in SS gear, tubes are naturally high impedance devices.
Tube amps do not have to have an output transformer, check out some OTL designs.
Tube amps do not have to have an output transformer, check out some OTL designs.
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There's distortion and there's distortion. If you have the opportunity, listen to a Harman/Kardon Citation II that's in good repair. That's the sound SS has been striving towards and hasn't quite got. 
A quality SS power amp can be the better choice with certain speakers. Big Thiels come to mind, as they exhibit hideous impedance dips down to 1 Ω. You can't get the gargantuan damping factor needed from tubed circuitry.
Proper mating of speakers and amps is crucial to obtaining good performance. A super efficient horn speaker will not sound good in combination with "sand", as the combination is badly over damped.
System synergy IS the name of the game and it can be obtained in several ways.
A quality SS power amp can be the better choice with certain speakers. Big Thiels come to mind, as they exhibit hideous impedance dips down to 1 Ω. You can't get the gargantuan damping factor needed from tubed circuitry.
Proper mating of speakers and amps is crucial to obtaining good performance. A super efficient horn speaker will not sound good in combination with "sand", as the combination is badly over damped.
System synergy IS the name of the game and it can be obtained in several ways.
See, this is not a lot of people here said. I very specifically asked and was told low distortion is everything. That's why I am confused. I always agree that there is distortion and there is distortion. You guys don't need to convince me on that. I am just repeat what quite a few people told me here.
I know for fact that tube guitar sounds more organic and warmer than SS, there is no comparison. But I was told here that it's exactly opposite in audiophile. People here using all sort of tricks to lower distortion. I have been reading Audio Power Amp by Bob Cordell, he did everything in the first few chapter to lower distortion. So which is it?
I can accept low distortion is everything, I can accept that tube gives the distortion characteristics that is pleasing to the ears. But I cannot accept both at the same time, that low distortion is everything but tube amps sounds better!!!!
I know for fact that tube guitar sounds more organic and warmer than SS, there is no comparison. But I was told here that it's exactly opposite in audiophile. People here using all sort of tricks to lower distortion. I have been reading Audio Power Amp by Bob Cordell, he did everything in the first few chapter to lower distortion. So which is it?
I can accept low distortion is everything, I can accept that tube gives the distortion characteristics that is pleasing to the ears. But I cannot accept both at the same time, that low distortion is everything but tube amps sounds better!!!!
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It's a preference chosen by the listener, if it sounds good then it sounds good Especially over extended periods of listening where fatigue can set in.
If fidelity (as in Hi-Fi) is the goal then lower distortion is desired, studios probably strive for high fidelity for they are in the business of sound engineering and any coloration to the recordings from playback equipment is a no no
Especially over extended periods of listening where fatigue can set in.If fidelity (as in Hi-Fi) is the goal then lower distortion is desired, studios probably strive for high fidelity for they are in the business of sound engineering and any coloration to the recordings from playback equipment is a no no
You have very big arguments against tube amps......but I will tel You. SE tube amp has very limited passive elements, about 10-20, but SS - hundreds! Every passive element decrease Quality of sound and is not wellcome to the structure.
And the tube sound is more clean, fresh, detail......Most important is that "the parts" cross vacuum from cathode to plate!
/my moto is HiEnd is back proportional to the number of composite parts/.
About OTs - my latest project - OTL-OCL 6AS7 Gen Electric is without OTs, that is for a level higher SS amps for $$$$.
I'd like to advice You, to compare every expensive SS amp with OTL Atma-sphere or big projects SE GU81, 300B WE, 2A3 RCA with Hi Quality speakers and You will sense the difference. /IMO, Electrical parameters are not very important, against the sense of pleasant sound/.
And the tube sound is more clean, fresh, detail......Most important is that "the parts" cross vacuum from cathode to plate!
/my moto is HiEnd is back proportional to the number of composite parts/.
About OTs - my latest project - OTL-OCL 6AS7 Gen Electric is without OTs, that is for a level higher SS amps for $$$$.
I'd like to advice You, to compare every expensive SS amp with OTL Atma-sphere or big projects SE GU81, 300B WE, 2A3 RCA with Hi Quality speakers and You will sense the difference. /IMO, Electrical parameters are not very important, against the sense of pleasant sound/.
Alan, you have it roughly right.
Your Point (4) is weak though. While it is true that a circuit occupying a larger volume will offer more problems with crosstalk, as any designer of switch mode power supplies usually gets to learn the hard way, in practice its isn't hard to get acceptable performance in tube amps with good construction practices.
Crosstalk between channels is not much of an issue in itself as almost all audio sources have not a lot of isolation in recording. However in class AB push-pull circuits, stray coupling from power rails back into input circuits is a pernicious source of distortion. Solid state amps for economic reasons are almost always class B, and suffer from this problem a lot more than tube amps, because in a class B circuit the current drawn by the output stage inherently contains a lot of harmonics.
In practice, you can't really tell beteen the best of tube amps and the best of solid state amps. There's too much focus on harmonic distortion in amateur audio circles. It was never so much of a focus in professional electronics.
It's actually easy to get very wide power frequency response in tube amps. The wide bandwdith in audio amps is itself totally inaudibile, but it is one way to avoid transient intermodulation distortion. This is where the driver, itself driven by neg feedback, tries to force the slower output stage to do something it can't. Fast power transistors cost big bucks, so in solid state amps we have to use other more subtle ways to eliminate TID.
In the 1950's, GEC released designs of several tube amplifers using KT66's or KT77's in ultralinear push pull, and push pull drivers. These amps had sub- 0.1% total harmoic distortion. Today, we can do 100 times better than that in solid state, and we can even do quite a bit better with tube amps, transformers and all!
But.... Noted RCA research engineer Harry Olson in the 1940's did some carefully designed experiments with audiences. He found that few people can detect distorton less than 1%. Somwhat later, similar work was done by Philips in Holland. They came to the same conclusion, and it was the origin of a 1960's era European consumer protection specification for "Hi-Fi". To legallly qualify as Hi-Fi, an amplifier had to have harmonic distortion less than 1%.
These results need to be treated with considerable caution, as audio sources are so much cleaner now, and people have got used to distortion levels much lower than was available form records in the 1940's and 1950's. But it is still definitely the case that competently engineered amplifiers, whether tube or solid state, will deliver distortion performance well below what you can hear.
Note that I said competently engineered! If the design is no good, that's a diferent story. It IS easier to get a solid state design wrong.
I have significant experience in the radio broadcast industry. When AM broadcastig was king, the better radio stations spent a LOT of money on studios - really good studio acoustics, very good practices for looking after records, limits on the number of times a record could be played, etc. But your typical AM transmitter was plate modulated by a Class-B high power audio amp, usually without any negative feedback at all! A few had NFB. Harmonic distortion, measured end to end from programme input to transmitter detected output was seldom better than 1% - some brands were worse!
When FM came in, distortion was only slightly better. The early generation of FM exciters with servo-stabilised reactance-modulated oscillators were doing well if the distortion was less than about 0.7%.
Note that even order distortion is just not very noticeable. The ear generates plenty on its own! Some people even find even order distortion pleasant! If you enjoy a Class A tube amp with nor feedback, that's what you will get. If you like it, that fine! Enjoy - its a free country.
Your Point (4) is weak though. While it is true that a circuit occupying a larger volume will offer more problems with crosstalk, as any designer of switch mode power supplies usually gets to learn the hard way, in practice its isn't hard to get acceptable performance in tube amps with good construction practices.
Crosstalk between channels is not much of an issue in itself as almost all audio sources have not a lot of isolation in recording. However in class AB push-pull circuits, stray coupling from power rails back into input circuits is a pernicious source of distortion. Solid state amps for economic reasons are almost always class B, and suffer from this problem a lot more than tube amps, because in a class B circuit the current drawn by the output stage inherently contains a lot of harmonics.
In practice, you can't really tell beteen the best of tube amps and the best of solid state amps. There's too much focus on harmonic distortion in amateur audio circles. It was never so much of a focus in professional electronics.
It's actually easy to get very wide power frequency response in tube amps. The wide bandwdith in audio amps is itself totally inaudibile, but it is one way to avoid transient intermodulation distortion. This is where the driver, itself driven by neg feedback, tries to force the slower output stage to do something it can't. Fast power transistors cost big bucks, so in solid state amps we have to use other more subtle ways to eliminate TID.
In the 1950's, GEC released designs of several tube amplifers using KT66's or KT77's in ultralinear push pull, and push pull drivers. These amps had sub- 0.1% total harmoic distortion. Today, we can do 100 times better than that in solid state, and we can even do quite a bit better with tube amps, transformers and all!
But.... Noted RCA research engineer Harry Olson in the 1940's did some carefully designed experiments with audiences. He found that few people can detect distorton less than 1%. Somwhat later, similar work was done by Philips in Holland. They came to the same conclusion, and it was the origin of a 1960's era European consumer protection specification for "Hi-Fi". To legallly qualify as Hi-Fi, an amplifier had to have harmonic distortion less than 1%.
These results need to be treated with considerable caution, as audio sources are so much cleaner now, and people have got used to distortion levels much lower than was available form records in the 1940's and 1950's. But it is still definitely the case that competently engineered amplifiers, whether tube or solid state, will deliver distortion performance well below what you can hear.
Note that I said competently engineered! If the design is no good, that's a diferent story. It IS easier to get a solid state design wrong.
I have significant experience in the radio broadcast industry. When AM broadcastig was king, the better radio stations spent a LOT of money on studios - really good studio acoustics, very good practices for looking after records, limits on the number of times a record could be played, etc. But your typical AM transmitter was plate modulated by a Class-B high power audio amp, usually without any negative feedback at all! A few had NFB. Harmonic distortion, measured end to end from programme input to transmitter detected output was seldom better than 1% - some brands were worse!
When FM came in, distortion was only slightly better. The early generation of FM exciters with servo-stabilised reactance-modulated oscillators were doing well if the distortion was less than about 0.7%.
Note that even order distortion is just not very noticeable. The ear generates plenty on its own! Some people even find even order distortion pleasant! If you enjoy a Class A tube amp with nor feedback, that's what you will get. If you like it, that fine! Enjoy - its a free country.
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Do all tube amps sound better? Do all SS amps sound bad?
It also depends on the application. Will you find tube amps doing sound reinforcement duty in a church, concert hall or auditorium? Or will you find SS amps there?
And lastly, it's sometimes funny when people/manufacturers strive for 0.0017% distortion in their amps, so it can connect to speakers that have 0.2 to 14% distortion in itself (more so at higher SPL). -- it's like all the work done on lowering distortion on the amp, gets thrown out the window anyway when connected to a speaker.
Loudspeaker Distortion At Low Frequencies Article By R. A. Greiner (Wisconsin)
In the end, don't worry about what other people think. Pick what sounds good to your ears.
Thanks guys, I'm with you that the right distortion can sound better. AND distortion of speaker and recording dominate everything. I just want to put it out because as I said, there are quite a few that insist on lower distortion is everything and for the life of me cannot imagine you can make a lower distortion tube amp than SS amp if everything is done right ( important that everything is done right, you can have mess up design in either side).
I made a mistake in my OP that I have two 4). I did a lot of pcb layout for RF and signal integrity design. Yes, it is possible to layout the tube circuit just as good, BUT it is going to be much harder. That's a fact. You have high impedance circuit that swing a lot higher voltage with longer leads ( bigger components), it's is going to be a whole hell of a lot harder to layout. Believe me, in my years of EE and manager of EE, good layout people is very very hard to find, even an engineer is not necessary a good layout person. I am one of those odd balls that love doing layout because I love to deal with signal integrity. I even layout boards for engineers that worked for me. Layout is easy to talk and very hard to do, for tube circuit, layout is a very big percentage of the design.
I hope the people that believe low distortion is everything can come join in. I want to hear your side.
I made a mistake in my OP that I have two 4). I did a lot of pcb layout for RF and signal integrity design. Yes, it is possible to layout the tube circuit just as good, BUT it is going to be much harder. That's a fact. You have high impedance circuit that swing a lot higher voltage with longer leads ( bigger components), it's is going to be a whole hell of a lot harder to layout. Believe me, in my years of EE and manager of EE, good layout people is very very hard to find, even an engineer is not necessary a good layout person. I am one of those odd balls that love doing layout because I love to deal with signal integrity. I even layout boards for engineers that worked for me. Layout is easy to talk and very hard to do, for tube circuit, layout is a very big percentage of the design.
I hope the people that believe low distortion is everything can come join in. I want to hear your side.
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Lower THD is not everything to me. "Sound" of amplifier is depend on some combination of their specifications like THD, S/N ratio, PSRR, slew rate, etc.
I have built VSSA variant that simulated result is worst than THD of my amp which is measured. But I like VSSA very much. And then I designed amplifiers using Current Feedback topology and Voltage Feedback topology with high slew rate. I found my self that I like amp with high slew rate. I will trade a little bit THD for slew rate
Some people like colored sound. You can make THD profile of SS amp like tube. H2 is highest, H3 is less than H2, H4 is less than H3, etc. Some people will think the sound like tube
I have built VSSA variant that simulated result is worst than THD of my amp which is measured. But I like VSSA very much. And then I designed amplifiers using Current Feedback topology and Voltage Feedback topology with high slew rate. I found my self that I like amp with high slew rate. I will trade a little bit THD for slew rate
Some people like colored sound. You can make THD profile of SS amp like tube. H2 is highest, H3 is less than H2, H4 is less than H3, etc. Some people will think the sound like tube
I'm a believer in low distortion but not as currently measured, with a single or (sometimes) with two tones. That's because music is very large numbers of smaller amplitude tones, and with a vast quantity of individual tones the dominant form of distortion is intermodulation, not harmonic.
But IM still cause by distortion of a single frequency. IM is from f1+f2, f1-f2, 2f1-f2 or 2f2-f1 etc. If you have no distortion, you have no harmonics, you will not have IM.
So the question is still whether it is more important to have the right distortion or no distortion.
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So post #1 is baiting, for the fish to bite, and post #5 is saying "Ha! I knew it! Gotcha!"
Don't treat us like idiots.
It does not reflect well on you as a person.To answer your question properly, you have to consider the possibility, "What if distortion is so low that it is completely inaudible?" Because that is where we have arrived with good modern SS amps. And you might have numerous friends here if you choose to debate that point to the ends of the earth, but in the end I can only say either read and learn more, or "talk to the hand". In the end, the valve amp argument is pure religion, so is the MOSFET amp argument, so is the single-ended amp, etc. We need to move on.
Would you rather have the audibly distorting amp, instead of the transparent one, because you have made a personal decision to like the sound of distortion more than the sound of the truth of the music as recorded? Then your goals are different to many of us here, who really would prefer to hear the MUSIC, and not to have any distorting character laid over it.
It was pointed out to you on the other thread you started in order to put down the modern SS amp, regarding speaker protection, that comparison with musical instrument amps is not appropriate. To play music, the artist tries to create a tone that he or she can use constructively. There is no truth to preserve. The amp can be part of that creation, if so wished. But to play back a recording of music, the music making is already done, and all that we want to get off that recording is the same tones that the musicians and recording crew created together. Unadulterated. The musicians, if they care about our experience as a dislocated audience, want us to hear the tones they created, not have them all smeared over by some layer of honey or other sonic flavour. Just like a master chef would be dismayed by us pouring tomato sauce over absolutely everything he or she sweated over to get 'just so' for our delectation. Such consumers are dismissed as philistines, buffoons, and if they insist that 'that's the way they like it', then the chef will feel entitled to serve up slops in the future. So that's a big NO to valve amp sound from me, in playback equipment.
And I hope we have seen the last of your baiting methods.
Maybe I am misunderstanding you but no, IM is not caused by a single frequency. It requires two or more.
Yep - but you used 'but' to begin your response so you must consider that what you've written contradicts what I said. However it does not.
If transparency is the aim (it is for me, to hear the recording better) then I plump for the latter. However low THD does not appear to correlate well with transparency (which I take to be low N-tone IMD, where N > 200 or so, a.k.a modulation noise).
IM is not cause by single frequency, it's cause by distortion. As you said, music is a collection of frequency, distortion of those frequency create IM. So it still boils down to the harmonics of a single frequency as all the frequencies will have harmonics. Those harmonics cause IM.
I don't know what make transparency, I was told low distortion gives transparency. I am just confuse what is important.
I always think the right distortion can sound very good. But I was told lower the distortion that better. And the tube amp definitely loss in the distortion dept. But it might sound better.So post #1 is baiting, for the fish to bite, and post #5 is saying "Ha! I knew it! Gotcha!"
Don't treat us like idiots.
That's where I disagree. Speaker and recording produce the most distortion. I think I covered this in a few post already as I was a musician for over 10 years. Anyone that play long in music knows that the real live music sounds nothing like in any recording. So you talk about how much you like the sound of the system, not how true is the sound to the original live music. It is a fantasy that people think they actually hear the true performance listening to even the best system in the world.
Not baiting, I just point out the inconsistency that I got here. I presented the technical facts on the first post that if sound quality is directly related to low distortion, then tube amp loose out completely. But obviously it's not true.
And if you don't like it, you don't have to answer.
Distortion though is a product, what causes IM is non-linearity, and I agree non-linearity also causes THD. So that leads us to consider transfer functions, although they're only useful when there's no frequency-dependent non-linearity (and there always is in practice).
You lost me - harmonics don't cause anything, they're the result of passing a signal through a non-linear network.
I suggest then ask more questions and make fewer assertions. That's the way to clarify confusion.
the "THD, and only THD" thing gets tiring after a while
You could raise the level of this discussion by actually reading some research, understanding “distortion” dimensions beyond THD, relation to Psychoacoustics
and I've tried to add real, meaningful content to the discussion over the years - hardly seem to make a dent in the people coming here, tossing about THD to beat whoever they disagree with over the head - used by both camps in the totally unsophisticated form this thread seemed to start with
we have the "THD meaningless," crew and their lot projecting a strawman meaning of "conventional audio measurements"
actual EE, audio designers do know how to make considerably more useful measurements, relate them to Psychoacoustic thresholds
http://www.diyaudio.com/forums/multi-way/121253-geddes-distortion-perception.html
an old post of mine:
what engineer ever looks at a single THD number? - look in any chip amp datasheet - THD is given in graphs vs level, frequency, load - many thousands of "single THD values"
and standards for IMD are pretty old too - longer than most engineers working lifetimes
from the Cabot review article: AES E-Library Comparison of Nonlinear Distortion Measurement Methods
Quote:
32. Read, G.W. and R. R. Scoville - "An Improved Intermodulafion Measuring System" Journal of the 45. Waddington, D.E.O'N- "Intermodulafion Distortion
SMPTE,February 1948.
33. Roys, H.E. - "Intermodulation Distortion Analysis as Applied to Disk Recording and Reproducing Equipment" - Proceedings of the IRE, October 1947.
Cabot and Hofer book chapter: http://www.eselab.si/doc/Chapter13_3.pdf
B&K has another good paper: http://www.bksv.com/doc/bo0385.pdf
Czerwinski Multitone testing paper's bibliography on distortion measurement goes back over a century AES E-Library Multitone Testing of Sound System Components'Some Results and Conclusions, Part 1: History and Theory
the recycling of old memes continues here - a post of mine from a decade ago:
Quote:
Originally Posted by jcx View Post
the repetitive and uninformed nature of this "discussion" frustrates me - the fact that a few people new to the field are overly impressed by a few old papers that happen to reinforce their preconceptions about willful ignorance of the objectivist engineering community, bad negative feedback, "solid state" sound ect keeps this ridiculous game of "telephone" going - everyone repeats the same old stuff
people only referencing Otala's cheering section would appear to be pushing an agenda by selective reference - andy_c nailed the flaw in the Otala/Gilbert analysis quickly as did Cherry in "Amplitude and Phase of Intermodulation Distortion" JAES V31#5 May 1983
distortion analysis has advanced substantially, P Wambacq & W Sansen “Distortion Analysis of Analog Integrated Circuits” 1998 is representative of where engineering analysis can go when the demands (= money) of a major market like DSL/ADSL engage the research community, Cherry, “Estimates of Nonlinear Distortion in Feedback Amplifiers” JAES V48#4 2000 is another jewel that clarifies and simplifies distortion analysis without the obscuring Volterra math
why not try reading a truly thorough and relatively recent review article: "Multitone Testing of Sound System Components - Some Results and Conclusions, Part 1: History and Theory" JAES V 49#11 nov 2001 by Czerwinski et al at Cerwin Vega - 119 references!
the paper sets a high standard in historical and engineering analysis of distortion and audibility - the art advances, why don't these "discussions"?
--------------------------------------------------------------------------------
You could raise the level of this discussion by actually reading some research, understanding “distortion” dimensions beyond THD, relation to Psychoacoustics
and I've tried to add real, meaningful content to the discussion over the years - hardly seem to make a dent in the people coming here, tossing about THD to beat whoever they disagree with over the head - used by both camps in the totally unsophisticated form this thread seemed to start with
we have the "THD meaningless," crew and their lot projecting a strawman meaning of "conventional audio measurements"
actual EE, audio designers do know how to make considerably more useful measurements, relate them to Psychoacoustic thresholds
http://www.diyaudio.com/forums/multi-way/121253-geddes-distortion-perception.html
an old post of mine:
what engineer ever looks at a single THD number? - look in any chip amp datasheet - THD is given in graphs vs level, frequency, load - many thousands of "single THD values"
and standards for IMD are pretty old too - longer than most engineers working lifetimes
from the Cabot review article: AES E-Library Comparison of Nonlinear Distortion Measurement Methods
Quote:
32. Read, G.W. and R. R. Scoville - "An Improved Intermodulafion Measuring System" Journal of the 45. Waddington, D.E.O'N- "Intermodulafion Distortion
SMPTE,February 1948.
33. Roys, H.E. - "Intermodulation Distortion Analysis as Applied to Disk Recording and Reproducing Equipment" - Proceedings of the IRE, October 1947.
Cabot and Hofer book chapter: http://www.eselab.si/doc/Chapter13_3.pdf
B&K has another good paper: http://www.bksv.com/doc/bo0385.pdf
Czerwinski Multitone testing paper's bibliography on distortion measurement goes back over a century AES E-Library Multitone Testing of Sound System Components'Some Results and Conclusions, Part 1: History and Theory
the recycling of old memes continues here - a post of mine from a decade ago:
Quote:
Originally Posted by jcx View Post
the repetitive and uninformed nature of this "discussion" frustrates me - the fact that a few people new to the field are overly impressed by a few old papers that happen to reinforce their preconceptions about willful ignorance of the objectivist engineering community, bad negative feedback, "solid state" sound ect keeps this ridiculous game of "telephone" going - everyone repeats the same old stuff
people only referencing Otala's cheering section would appear to be pushing an agenda by selective reference - andy_c nailed the flaw in the Otala/Gilbert analysis quickly as did Cherry in "Amplitude and Phase of Intermodulation Distortion" JAES V31#5 May 1983
distortion analysis has advanced substantially, P Wambacq & W Sansen “Distortion Analysis of Analog Integrated Circuits” 1998 is representative of where engineering analysis can go when the demands (= money) of a major market like DSL/ADSL engage the research community, Cherry, “Estimates of Nonlinear Distortion in Feedback Amplifiers” JAES V48#4 2000 is another jewel that clarifies and simplifies distortion analysis without the obscuring Volterra math
why not try reading a truly thorough and relatively recent review article: "Multitone Testing of Sound System Components - Some Results and Conclusions, Part 1: History and Theory" JAES V 49#11 nov 2001 by Czerwinski et al at Cerwin Vega - 119 references!
the paper sets a high standard in historical and engineering analysis of distortion and audibility - the art advances, why don't these "discussions"?
--------------------------------------------------------------------------------
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