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Old 12th March 2009, 07:16 AM   #1
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Hi,
this time it`s about the extremely popular but likewise extremely meaningless THD, intended as a figure of merit to prove the excellency of amplifiers beyond a reasonable doubt, provided by simulation software employing ideal parameter values and mathematical constants, being completely unable to analyze course of events. In this way, it never disappoints you, you can`t get anything but great results to be supremely proud of, although you might have minor difficulty explaining the mediocre sound. Of course, that figure in close vicinity of zero has nothing to do with reality, but don`t be particularly sad about this inconvenience, THD is just as meaningless when measured reliably with adequate equipment, because it does not show the harmonic content, which has overwhelming and decisive importance. For instance, the perceived difference between a class B and class A amp having the same THD is huge, that is in favor of class A and not even a drastically higher level there would change that impression.
Furthermore, the brain does not process sounds according to the commonly postulated linear scale, rather according to its own scale. Persisting in forcing that "linearity" on the ear is condemned to fail.
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Old 12th March 2009, 09:22 AM   #2
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Default Our concerns about numbers, harmonics, distortion, square waves, THD, measurements


Post your ideas about.


Lumba is especially invited.

ear plus brain cannot process that information.... the thing works slowly because bio-chemical.... the square wave when reach ear plus brain looses the 90 degrées corners, because system cannot do that.... corners turns rouded, and what goes to brain is another thing very different from a square wave..something rounded enters.

So...when we use square waves and we make our efforts to make the square wave reproduced correctly in shape we are doing almost nothing...as brain will perceive another thing.

Numbers and THD are nice indication..but real world is filled with noises, reverberations, atenuations, distortions, harmonics and the real thing is not perfect...what means perfection?..... to do all those things?...... could be..but studios control all stuff and produce to you something very synthetic..something very filtered... a controlled product.

To study psycho acoustic is something we need to understand, a little bit more, such kind of reality...we can listen an old portable battery radio that cannot reproduce frequencies bellow 250 hertz (cutted, blocked internally, filtered, small condensers into stage input) and the speaker cannot go so deep... and they did that to avoid you to listen the mains hum when using old style AC to DC converters..so...this way....not beeing able to reproduce low frequencies, the mains frequency would not bother...... but people listen bass... this may be memory or musical experience...something our brain does completing the sound...so.... brain is always processing, adjusting the whole thing.

If you love someone and that woman call you by phone...and the environment is noisy.... transit, horns, people talking, wind, noises from everywhere...but you love that woman..and she call you.... could you perceive you listen only her voice and nothing more..the noises are filtered, deleted, erased from the system... only her voice is listened...why?... brain did that.

So... we use numbers to explain and evaluate...but the study of psycho acoustic will be more competent to help us to evaluate....

Are you sure humans dislike harmonics?.... and real sound has not distortions?... i am not sure....i have suspections the opposite...we love harmonics...harmonic is music..and distortion may be fine, depending what kind of distortions.

Our digital world is virtual...what means power measurement when you use simulator (almost nothing)...supply will drop voltage...real world is another thing...speaker system will react with EMF... well.... numbers and simulators are indications of possible maximum power...real world is different.

Distorted guitars are nice...why?

regards,

Carlos

.................................................. ...
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Old 12th March 2009, 10:01 AM   #3
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Default People may say:


If ear plus brain cannot process square wave 90 degrées corners, so, may recriate this wave shape when receiving rounded corners.

Yes... it is possible...but what will happens with the real rounded corners ... the one is rounded into the original...will it be "squared" too?

Do the wave forms... the cicle has encoding..say... something alike tracking indicators..tracking numbers?

Will brain recognize the square wave that had rounded corners because bio chemical processing to restore the waveshape?

Maybe square goes to sinus.... but we can perceive clearly what is sinus and what is square wave.... you see... brain is much more clever than we are... we are "conscience"...there are much more to study.

Carlos
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Old 12th March 2009, 11:10 AM   #4
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Default In many ways.... we...humans...use to search for hairs into bald head


You see.... down the sixties or seventies they have made the IFH institute rules about how to measure amplifier power.

You can see how wrong we can be.... and was followed and accepted by everybody.... factories started to make their specifications following IHF rules.

They said you could plug into power amplifiers a burst of signal many times bigger than the maximum allowable... this means hard distortion...the output was crazy...and they did that with only one channel beeing used..... very crazy that.... unreal.... as amplifiers use two channels simultaneously and we do not use burst of signal entering with so big levels, as we do not listen distortions.

And only one channel.... having time to the supply to gain voltage after the last burst of signal have entered...so.... measurement was many times bigger than the real thing....

And this was the rule...and nobody discussed there.

We are treating humans alike osciloscope...we are not osciloscope!

Carlos
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Old 12th March 2009, 11:27 AM   #5
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Default In the seventies, while i was into the University, studying Psychology


I have found interesting things.

I have decided to measure brain waves and audiograms.... i have selected groups.

The rich and snobish girls that only talked about their travel to Europe... always informing about wealthy.... very futile people...and they are a group...only talking between them... a close group

The simple people, not snobish, or poor, the ones was thanking God they could study in so famous and expensive University...humble people..and they have their own group.

The depressive people, the ones had not self confidence.... the ones decided for psychology trying to discover their own personal problems.


I was in the second group....and measurements into laboratory show me the groups had consistence into measurements.... i had different measurements into each one of those groups.

Well.... after one year the laboratory was closed and i could not study the subject anymore...also i had not time because working into a Broadcasting Television Station....

Since that moment i perceive people were different related how their "system" works...how brain works.... and frequencies were the results.

I could not continue... found nothing to study about...and found no one more skilled to give me inputs.

I see we continue delirating.... very crazy thing to bother about 0.001% THD when speaker produces a mess much bigger than that.

I am searching for inputs about.... more than 39 years thinking about and i have discovered few thing but i am still very ignorant...... but also i can see there are many folks much more delirant than i am.... following the "stablishment"... the "status quo"... without think about.

Perception... psycho acoustic is the matter that interests me.... and i think is something that should be interesting for many folks too.

Carlos
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Old 12th March 2009, 11:31 AM   #6
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Default Well... i have provocated a lot...now will be waiting someone with courage


to contribute....it is hard to say those things.

Imagine when someone said world was rounded.

When people said earth travell around the sun and that we were not the center of the universe.

The theories of Einstein.

Everything sligtly different is scandall.

I have discovered nothing.... those things were around us since the start of high fidelity concerns...people decided to study oscilograms....but we are not osciloscope folks!

Carlos
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Old 12th March 2009, 12:11 PM   #7
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IMHO, distortions in the time domain are much more audible than harmonic distortions. By this I mean the relationship of high frequencies wrt the lower ones. This is one reason why some of us don't like large electrolytic coupling caps.

Also IMD can be quite harsh.
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Old 12th March 2009, 12:11 PM   #8
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one way of looking at it is this:

every waveform is a mixture of sine waves.

THD is only valid within the audible range and a bit beyond (the ear does process information up to about 50khz, even though you can't "hear" it, as it's processed as spatial information).

if you add harmonics to a pure sine wave, you've changed it's shape and harmonic content. you have changed it's sound. amplifiers shouldn't change the sound. unless you're a guitar player and you WANT the amplifier to change the sound
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Old 12th March 2009, 12:33 PM   #9
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Very nice reading Carlos and Lumba, i agree.
But we have to remember it´s a long chain of components from the microphone at the recording-movement till the sound comes out of your speakers at your home.
Every singel stage ad some sort of distortion, and i think it´s confirmd that 0,1% distortion is appreciable.
Good sound-engineering has benefits for the whole chain and in the end your experience in the favorite listening chair.
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Old 12th March 2009, 01:18 PM   #10
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Bud's whole EnaBl thread is pertinent to all this - here we have a treatment that seems to change the perceived sound from a driver (agreed by most who have heard it) and yet there is no significantly measurable parameter to explain this sonic change.

And the same old arguments flared up on that thread between those who maintain that measurements are God & those who don't. Some people call this the objectivists Vs the subjectivists but I prefer to think of the subjectivists as those willing to concede that science can't explain everything (YET)

Bud has an interesting theory about hearing on that thread, I can't remember what he calls it but it relates to our biological survival mechanisms and the fact that our ear/brain system has been trained to hear a discordant noise among a background of noise - this might be the noise of a snake in the grass. So if there is a discordant noise our attention is immediately drawn to this - the same happens in music & our mind is forced to focus on this discordance = listener fatigue? So identifying what is discordant is the secret, perhaps?

There is another thread on here about a guy who had tinnitus and his theory on hearing after he rid himself of tinnitus by retraining his brain's area of attention in the sound field

I agree with Carlos, the focus of attention should not be on simulators & THD numbers, etc but how the ear/brain truly works.
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