[AKSA]

OK, here goes, gotta get you guys chatting.  Some controversy......

1.  Low THD is just one requirement of good audio reproduction.
2.  The recording process is inevitably flawed, and cuts some of the higher harmonics from the material, leaving a thin, at times surgical sound.  This happens because mikes are directional, and recording off axis cuts high frequencies.
3.  Playback, to sound natural, must reconstitute some of these lost harmonics.
4.  Tubes in single end do this nicely, adding H2 for richness and H3 for sharpness and focus.
5.  Some recordings add this too by using single ended circuitry for processing;  nowadays it can be done digitally very easily.
6.  Added low order harmonics create a psychoacoustic masking effect on any high order effects present.
7.  Added H2 and H3 need only be VERY small;  typically 0.03%.

Conclusion:  The straight wire with gain is not a good design model.  Any harmonics (I won't call them distortion!      ) added during playback must be low order, no more than H4.  The difference between a trumpet played soft and loud is reportedly an extra 0.05% of H5, H7 and H9 over the fundamental, suitably adjusted for amplitude;  yet we humans hear this distinction very acutely.  The objectionable nature of high order harmonics is well known and responsible for our surprising perception that some amps with very low levels of THD sound dreadful, yet some SE triode amps with 2% sound sensational.

I invite comments, guys.  This is my current thinking on audio, but there MUST be something to disagree with here....  If someone can bring more information to this debate, I would be very grateful!

Cheers,

Hugh

[Marbles]

Low vs High

Odd vs Even


I thought you wanted even order and didn't want odd.

Now your telling us it's you want low and not high?

How does all this work????

[AKSA]

Rob,

It's pretty complicated;  not intuitive at all.

Second and third harmonic are both musical.  So is four.  But fifth starts to get a bit irritating;  try this on a piano.

Perhaps we should take our cue from tubes.  Their transfer function, power 1.5 (Child's Law), creates mostly H2 and H3, with some H4 and tiny portions of H5.  The relative proportions change greatly with operating point;  hence the concern to get the precise, melifluous address of the tube.  If this is true, then it perhaps follows that low order harmonics at very low levels are the go.......

Cheers,

Hugh

[brj]

I laud your efforts to address a perceived problem, but what would it take to address the problem at the source?  In other words, how hard would it be to get the extra information included in the recording to begin with, rather than guessing at the proper proportions during the amplification stage?  Is it not done for genuine economic or technical reasons?

[AKSA]

BRJ,

The better sound recording engineers are probably doing it anyway, according to their experience of what sounds good.  Asky Quincy Jones, I'm sure he has views on this......  This partly explains why some recordings are so good, most are ordinary.

I know of one DJ in Sydney, Australia who uses an H2 'augmenter' between his microphone and the console.  This has earned him, over the years, the moniker of 'golden tonsils'.  His spoken voice up close and personal doesn't sound half as good.....

Cheers,

Hugh

[brj]

Thanks for the response, Hugh!

I'll apologize now if it appears that I'm veering this topic off course.  I've just always preferred to address a problem at the source, rather than "band-aid" it somewhere else.  It may be that addressing the missing harmonics in the amplifier section is the only way to resolve the issue, but I don't yet know enough to even accept that as fact.

The better sound recording engineers are probably doing it anyway, according to their experience of what sounds good.  Asky Quincy Jones, I'm sure he has views on this......  This partly explains why some recordings are so good, most are ordinary.  Aren't modern microphones good enough, or does it simply cost enough that the economics work out.

I know of one DJ in Sydney, Australia who uses an H2 'augmenter' between his microphone and the console.

I wasn't thinking so much about harmonic additions added by the recording engineer to make a previously recorded track sound "good", but recording enough of the original information that no additions are needed.  In otherwords, why aren't all of the original harmonics recorded to begin with, and what would it take to change this?

This has earned him, over the years, the moniker of 'golden tonsils'.  His spoken voice up close and personal doesn't sound half as good.....

 I wonder what his answering machine or voice mail message sounds like!

[AKSA]

BRJ,

As further background to my assertion, I'd highlight the technology of microphones.  Since, owing to small diaphragm size, a modern mike will always be directional to some extent, it follows that correcting the problem at source - right at the mike capsule - would be a great idea.

In fact, this is done on the top end Neumann and AKG mikes.  These are German products, and very expensive.  Guess what?  They use a tube stage to amplify the output of the capsule.  Ask any muso, the very best mikes are 'tube' mikes.  The tubes employed are tiny;  the so-called pencil tubes from the fifties are commonly used.

Further interesting facts:  what about the electric instrument market?  What are the best amps here?  Are they tube or SS?  Once again, we find that Marshall, Fender and Vox dominate this market with tube amps, and their design is deliberately 'colored' to accord with the musician's taste.  You hear terms like 'crunch', 'fuzz', 'tubey' - all betoke a colored sound, which SS is hard pressed to supply.  These are not exactly 'straight wires with gain'.  Listen to an electric guitar played without amplification;  thin, weedy, anaemic, uninspiring, even with the ear only inches from the strings.  Fine, a bass guitar can use a powerful SS amp, but a lead MUST be a tube beast - nothing else will do.

Cheers,

Hugh

[JohnR]

Hi, I am by no means an expert but I was doing some research into microphones recently. I was curious as to why there is such as thing as a "measurement" microphone as distinct from a "recording" microphone. And the answer is that even for acoustic (classical) recording, engineers use a combination of different microphones with different characteristics (freq response and polar response) to achieve the sound they *like*. I don't recall mention of distortion characteristics but that probably figures into it as well. The best-measuring omni-directional mics are in fact are sometimes just relegated to the role of "ambient"  mics.

FWIW, which is not much

[bluesky]

Dear Hugh

Is this thread a byproduct (at least in part) of Mr Simpson's (editor of Silicon Chip magazine)  numerous editorials stating that tube amplification is incedibly poor compared to "modern" solid state amps?  Mr Simpson bases his stance purely on measurements.

Something I found very interesting was that the latest issue had an article on their new preamp and it went on and on about measurements but it did not talk about what it actually sounded like!  

I have only heard a couple of tubes amps and the first was quite poor in my opinion. However I recenty auditioned a couple of tube amps and was very imressed.  I have recently befriended a retired person who has numerous tube amps as well as the Silicon Chip Class A designed amp, which gives an astonishing 0.00006% THD figure.

So what does my friend prefer to listen to.......his tube amps!

Not a great contribution to this thread I know, however I am going to build a Darling SET amp purely to find out about this tube stuff for myself.  The Darling amp can be built very cheaply, this is especially so when you have been given all the tubes and most of the other caps and resistors required!

Cheers

Bluesky

[AKSA]

Hi Ian,

Yes, largely true.  I am trying to scotch the rumor that objectivism rules;  low THD, high slew rates and ruler flat frequency response really has little to do with the perceived quality of the sound.  It does have a lot to do with measured performance, but I've noticed that trying to get any measure of what an amp sounds like on real music by using a Distortion Analyser is like trying to explain the difference between red and blue to a blind man........

The fact is, fifty years of some of the best brains in the world following the notions of 'straight wire with gain' has delivered good amps with no more correlation to good sonics than eating well guarantees you won't get sick.......

I really think we are measuring the wrong thing, and this conviction, together with my own hunches and intuition, has led me down a different path to most designers.  I cannot say I'm right, and they are wrong - this smacks ironically of the only soldier marching in step - but I don't believe this approach is any more incorrect than others, and recent retracing of some R&D steps I took years back has only confirmed this approach.

Cheers,

Hugh

[Joules]

Behold the turtle, who only makes progress while sticking his neck out !!!

[JoshK]

Geddes has an interesting article (I read his PP pres which doesn't have that many detail) on measurements that correlate with actual hearing. They do some ABX tests and show that THD & IM do not correlate with hearing but his Geddes measure (function of higher order harmonics) correlates very highly.  He goes on to say that this is applicable with both speakers and equipment.  

To me it makes a lot of sense, if you are going to use measurements as objectivism then why not use better measures that actually relate to the way we hear?  The standard measurements are not the only measurements, they are just the ones that were easy to do so they caught on.

[Seano]

In my experience, what we choose to measure is driven by what we think we understand about the interaction between that being measured and the wider world.

Ultimately we measure only what we 'feel' (or what experience tell us) is practical and cost effective to measure then try to fit the resulting data to the current paradigm.  If it doesn't fit.......then we probably measured it wrong or we decide we don't know enough about the interaction between the measure and its world....

Just as one cannot describe the health of our rivers by just measuring nutrient levels we can't expect to describe the quality of an amplifier (or any other piece of audio jewellery) by its distortion characteristics....

In my world, there are measurements and there is perception. They may not always agree....but they both rule.

[AKSA]

Joules,

Behold the turtle, who only makes progress while sticking his neck out !!!

I really like this - it encapsulates the methodology of most scientific advances, slow, measured, exposed, vulnerable - and quite often, serendipitous.  Who knows what the turtle will come upon in his travels - his eyesight is poor!  

I don't subscribe to the belief that science advances in leaps and bounds;  all technical progress is painstaking and piecemeal - read Leonard Bickel's 'The Story of Uranium' to see how the fission bomb - and the reactor - was developed.  It was years of detective work, theorizing and math which brought these advances, even the calculation of U235's fissionable mass consumed a team of mathematicians for years!  Scientific advance is often two steps forward and one step back.  (That's something the turtle never does, he always goes forward, no matter how slow!!)

I'm always struck by how little scientists and engineers (but perhaps even more significantly, marketers!) read the history and philosophy of science.  To me it seems that any sense of perspective can only be won by studying what has gone before.  Only the history can signpost the way ahead.  In this connection science fiction is very useful.

I wanted to start some debate on the notion of measured performance, and its correlation with perceived sonics.  The world is full of 'why me' audio gear, all of it designed to the same scrupulous standards of low THD, flat FR, high slew rate - yet so much of it is ordinary and there is little correlation with these figures and the really good sounding gear.  Given the considerable distortion artefacts in vacuum tubes and their peerless sonic performance, it's no wonder there are two distinct camps with daggers drawn......  This set me on a quest years ago to try to narrow down some of the reasons for this dilemma, and the most plausible would appear to be Earl Geddes' well researched paper referred in the previous post.

Geddes has an impeccable career in industrial noise control, centered around the auto industry (he worked for Ford for years) and now in audiometrics, with a partner in a consultancy.  He's well qualified, and very thorough.  The paper shows good math rigor, and a very circumspect eye for detail and direction.  It really does give a credible explanation for why audio gear sounds as it does.  Recommended.

Cheers,

Hugh

[Joules]

I applaud what you are presenting. I've offen wondered about this. It's real good to read some one elses thoughts on poeple and sound and engineering. I knew there was a good reason for geting mix up with Aspen Amplifiers - Good sound and stimulating thought. Tell us more and maybe I might be able to ask an intelligent question.

[ehider]

I think you've brought up a very interesting point with this thread .

In my experience there is NO DOUBT that there must be something in the "high-end Audio land" that verifies your idea that we may actually need to deviate a bit from "accuracy" in order to better re-create the actual event. An example that comes to my mind is with the lauded and loved by many "Magnepan" speaker line. Those speakers are obviously interjecting additional sound into the room that was not in the actual recording in the first place (in terms of out of phase information to direct sound ratios at the very least). Every time I hear a set of Magnepans there are certain things they do more accurately in terms of sounding more real than any point source speakers I've ever heard! Then again, they also add that "something out of haziness" signature to many other parts of the music event that isn't necessarily "more accurate" sounding in my opinion too. The Magnepan analogy is just a start to the idea of deviating from absolute accuracy in order to get "more accurate sound to the listener" in my experience .

IMHO the same sort of thing happens quite a bit in tube equipment too! After a long a winding road down the varied path of ultra exotic solid state gear I found myself diverging into tubes. It was damn hard for me to swallow as an engineer myself because I just know that tube gear is not more accurate in terms of passing the input signal to the output without changing its character! Yet... I found myself getting more involved in the listening experience. Many, many times I felt the voices and instruments sounded MUCH more real .

How can this be  My only answer (at this point in time)  is that there must be losses in the recording event that need to be added back into the reproduction chain in order to bring the whole event full circle towards a more real sounding experience.

Talk about a quandary to "what is more accurate sound reproduction equipment" and why! It now seems to me like its just so damn subjective and flies in the face of many scientific measurables  

[jules]

Can I suggest that the idea of "accuracy" is and always has been a myth?

Everyone must have had the experience of that moment when an orchestra fades into the background to give the stage to a solo instrument. Yes, you can tell that it's an oboe and not a clarinet but what you hear is only a fraction of the real sound of the instrument up close and personal.

So why is this surprising? Here's the chain ....

source ....

gap between source and mike: [Often this is many metres. There's a good reason why vocalists have a hand held mike centimtres from their mouth]. For every metre you move away from a source the sound that is picked up changes. A directional mike is only a partial solution ....

the microphone: I'm guessing here but surely there's as many possibilities for mike types/feel as there are for those speaker things at the other end of the chain. It would be great if there was a recording/miking circle on AudioCircle. ...

the RECORDING STUDIO ... need I say any more!! [Herein is a licence to fiddle with sound. Anyone want to suggest that this bit does anything for the "straight wire with gain" theme?] ...

the part of the chain that occupies these forums: CD player, pre-amp, amp, speakers etc etc.

I would suggest that large amounts of sound are lost in the many stages  of reproduction that rarely get a mention on these forums and the art of producing a great amp is not to go into a state of denial where it is possible to claim that the measly remnant we hear is "distortion free" [What about the stuff that just isn't there any more?]  

I suppose that some sort of sculpting to enhance harmonics has to be recognized as a necessary evil but it's a difficult compromise to be comfortable with.  Brass, wind, string and percussion instruments vary widely in the overtones/harmonics they produce. An amp tailored for the harmonics of a trumpet might not be so well suited to a flute. There was a post on AudioCircle a while back by someone who changed tubes for different types of music. Maybe that's the closest we can get from one amp.

Hugh is clearly much more aware of the technical challenges here than I or 99% of the rest of us and I much prefer to trust his judgement in acknowledging the necessity of compromise to that of someone who has the naivety or stupidity to suggest that perfection is a realistic goal through the pure brilliance of their technology.

Jules

[_scotty_]

It seems to me that the goal of high fidelity reproduction should start with the
concept that the source should be viewed as having an initial distortion level of zero.  Any added distortion or corruption of the signal before it reaches our ears is a deviation from the original base condition.  It is a given that information has been lost in the recording process and there is an inherent
level of distortion present in the original recording.  I cannot see how adding
more distortion of any kind to the original signal serves the goal of preserving the original information.  If there was music present when the recording was made it should still be there when it is reproduced without
having to enhance it by adding distortion. I think once information is lost
anywhere in the chain it cannot be restored. You can't know what information is missing from your recording unless you were present during the recording session. You don't know what you do not know.  I think the less distortion of all kinds that is introduced by our reproduction chain the better off we are.  The idea of adding enhancing levels of 2nd and 4th order harmonic distortions to an amplifiers transfer function is an inherently flawed premise.  These harmonics are added to the entire content of the signal and not just to where they might be judged missing if one were present during the original performance that the recording was made from.  There is nothing wrong with prefering the reproduction of music by an amplifier with this sort of transfer function and we all listen to the gear that we prefer but I feel that
the deviation from the goal of high fidelity reproduction should be acknowledged.  The decision has been made that the sound of the original
recording is not deemed "musical","real", or pleasing enough, without alteration.
 As far as our available measurement capabilities are concerned they appear to be woefully indequate in defining the totality of what we experience when we listen to a piece of audio gear. I  think Richard C. Heyser was ahead of his time when he identified the  presence of Transient Dynamic Non-Linearity in our reproduction chain as the major source of distortion that is not seen by conventional measurement techniques.
Scotty

[gonefishin]

I just don't think most audiophiles want accuracy.  They don't want the sound of a trumpet, the sound of a real drum kit (let alone real cymbals)...real voices?  Doubt they would want that either.

     Nope.  I think audiophiles (and consumers) have pushed the audio industry in just the direction they would like it to go.  

   Perhaps this may be the largest points of difference between some tube amps and some SS amps.  I've heard it said before that a tube amp sounds good, despite it's numbers.  Not because of it.

    But I really do believe that thru the 70 to the present.  Audiophiles have pushed (no) demanded that certain components meet certain specifications.  So...low and behold they have gotten what they've asked for.  Components that perform to a certain obtainable level of measurement.  When a new amp or speaker comes out...and it meets a new set of measurements or criteria (even if advertising B.S.).  It won't be long after that other makers also meet this new "standard".  It's almost like keeping up with the Jones family...except they don't really have anything I want.  But the audiophile has gotten exactly what he/she demanded.  Many times a sterile one dimensional amplifier or speaker that meets a certain criteria.

    Now look at the tube amps...both old and present.  Many are made to simply sound a certain way.  Like it or not...take this one or leave that one.  Many are made with the sound as the major influence over measurements.

    What many tubies forget when they talk about what they think are superior amps.  Is that there are an awful lot of tube amps out there that sound (ed) like crap!  It's not one certain topology...it's the implementation within the limitations.

   For me...give me tone, clarity, a wide dynamic range with a low noise floor...little compression and the ability to move air while maintaining a solid image and normal soundstage.  Most times I would only blame the speakers, amps, preamps, room and positioning for not coming close to achieving this over the source material.  Sure, there's a lot of junk out there...but there's some dang nice sounding CD's too.

    Oh...blame the CD Players too...many times the modded versions that have polished the thing so fine that it sounds all delicate and pristine.  But they've taken out the dynamics and the tone to add THEIR own hand into the mix.


   *step down*  yes...I did hold back and erase most of what I had written

    *in my best Hugh Dean voice* g'day

     dan

[_scotty_]

Dan, I have to agree with you, a lot of what is produced today reflects
what the manufacturer feels the consumer wants.  You can't blame the manufacturer for building a product that he thinks there might be a demand for. I recall remark made to me a while back by a friend of mine. He said it is no problem building better equipement what we really need is a customer
with better hearing.  
 I also have noticed that "life" or a dynamic quality is very fragile and is frequently an early casualty of the "audiophile" sound although the converse also seems to happen almost as frequently,tonal and timbral accuracy as well as the frequency extremes are sacrificed for perceived dynamics.
That old adage may apply here,"be careful what you ask for, you just might get it."
Scotty