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[Jim Williams]

Please give me one measurement that predicts the perception of what the human hearing registers.
Leave out transducers, that field is even more complicated. Lets narrow the case down to analogue amplifiers.

How about THD+noise? Most people can detect that after about 2~3% in transistor amps with odd harmonic partials. Some do better but have more experience in detecting these errors.

The problem with euphonic selective analysis are the results are in the ear of the beholder. Everyone's hearing is different, everyone's ear shape is different, everyone's taste is different.

Objective tests avoid those variables. Test gear will work very well in finding errors. It will not tell you what you like to listen to.

[Uwe]

"To degrade human perception as subjective and influenced by bias and psycho acoustics is nonsens.
Blind tests based on scientifically and statistacally respected methods give reliable conclusions."

And yet, it is exactly properly conducted (double) blind test which have convincingly debunked the pseudo scientific claims for practically all snake oil claims for the affect of cables, line cords and connectors on audio transmission and perception...

[polypals]

Thanks Jim for your suggestion.
I have to admit my carreer in audio started when vacuum tubes were still being used, not only in high grade microphones.

Soon after the introduction of solidstate amps we found these had to have THD figures at least ten times better than the ones found in tube amps to get similar audio quality.
So much for measurement that gives results on which can be predicted how amplifiers sound.

Noise can be measured and compared, no problem with that.



Uwe,

I am not talking about esoteric gear like cables with silver and gold conductors, parts that were given the cold treatment and so on.

My thesis is about allowing our ears to judge new equipment as final test before this gear is accepted for professional use.
This prevents the kind of disasters I witnessed working for a major record company that had its mixers constructed in house. In house to be understood as designed and made by a sister company.

A junior balance engineer, younger and handsomer in those days. With a collegue we were comparing a
power amp design made by me in one of the control rooms of the studio.
We compared the new design against the standard monitor amp.
To adjust the output levels we used the mixing console just to correct the sound level.
After several hours I found a discrepancy in what we heard. We used other channels more strange things happened.
I suggested to my colleague the channels had audible differences. He laughed hard and said you lost your hearing after too many hours testing, this is state of the art equipment. Impossible.

Next weekend we started from fresh listening to the various channels of this mixing console.
In a blind test I could identyify several channels.

The studio manager heard what we had discovered.
He asked if I could set up a test to proof what we discovered.

What did I need? A maintenance engineer that could align three channels from various generation mixing consoles to give exactly 0 dB amplification. We had a small box containing a threefold selector switch.
The new power  amp design was used with a standard monitorspeaker to play a selection of records, no masters just LP records.

The test was so convincing all my colleagues from recording picked the correct generation channels.

My point is: We are all interested in achieving good audible results for recorded music. Forget about hi fi.
With some exceptions most recordings sound more impressive than the live performance, with an exception for some classical recordings.

Please answer this question:
How could a leader in the industry in those days end up with expensive gear that was unsuitable for professional use?


Please note.
Although this happened several decades ago I choose to be discrete and do not mention the company or persons involved.
Just drop me a PM if you want more information.

 

[David Satz]

polypals, we each make our observations and form our opinions. Human nature is to pay more attention to those occurrences which reinforce our own expectations and beliefs and our sense of how wise and knowledgeable and experienced we are. As a result, each of us will tend to feel well justified in what we believe, and to think that we know better than anyone who would disagree with us.

If audio is your hobby, there's really no reason ever to burst that little bubble. It is very pleasant to live there; many people do. I don't mean to say that you're in that bubble while I am not--although admittedly that is what I tend to feel when I read your posts. I can only expect that you would feel similarly if I posted my (very different) opinions, if you were to read them.

The problem is that neither of us, relying solely on our own senses and intuition, can tell at a given time whether we are inside the bubble of "confirmation bias" or not. We should therefore realize that we will probably tend to feel that we are right (and smarter than others) and that the other is wrong (and we are smarter than them), irrespective of the actual facts. Our senses and intuition give us absolutely necessary, but not sufficient, information for recognizing what we can consider to be true. People fool themselves all kinds of ways when they ignore that distinction.

[polypals]

Thanks for your observations that are touching filosofical areas.

Again I read reluctance to trust human perception. What gives engineers reason to trust the human ear? If I compare this attitude to photography no professional photographer distrusts his eyes.

I know amongst amateurs there is a lot of gimmicking that is not based on sound research and tests.
To conclude this attitude exists likewise amongst professionals is to say it mildly incorrect.

In the early seventies there was a trend to cut records without using tape.
Guys interested in hi-fi agreed these records sounded much better than records that were recorded on tape. During those sessions I once played these records over tape, straight from the playback amp from the recorder. Nobody in the audience noticed this.

I am well aware that suggestion and incorrect methods to compare equipment auraly can give unreliable conclusions.
Still I defend the habit to judge new developments with my ears.
After all we are all interested to get better aural results.

[Jim Williams]

Thanks Jim for your suggestion.
I have to admit my carreer in audio started when vacuum tubes were still being used, not only in high grade microphones.

Soon after the introduction of solidstate amps we found these had to have THD figures at least ten times better than the ones found in tube amps to get similar audio quality.
So much for measurement that gives results on which can be predicted how amplifiers sound.
Noise can be measured and compared, no problem with that.

This is why I said "odd partials" as transistor amps tend to have a bit more 3rd and 5th harmonics than a decent tube power amp which is dominated by euphonic 2nd and 4th harmonics. Most listeners will accept 5% THD from a tube power amp if the harmonics are even ordered, those tend to add a musical 'air' to the sound many find pleasing = euphonic response. I call that the 'aural excitement' effect.  It's also why we electric guitarists prefer tube guitar amps.

Transistor amps require very low THD+noise specs as any odd harmonic partials are easily detected by the listener. You also have other factors like slew limitations affecting the transient response.

Since both topologies have been well designed and developed, it's now really about personnal taste as you can get very accurate transistor power amps and there are some tube power amps with decent specs that also sound rather neutral, the Futterman designs come to mind.

With modern test gear like Audio Precision, one can now days measure and predict with some success the sound of these designs.

[polypals]

Sorry Jim, I do not agree with even/odd harmonics theory.

It depends on what tubes are being used what kind of harmonics are generated.
Triodes give even harmonics, penthodes generate odd harmonics.

In poweramps the distortion generated by the output triodes will be virtually zero provided the output tubes are paired.

I wonder about the 5% figure you quote. Any amp with that amount of distortion no matter what harmonics the 5% consist of is unsuitable for monitoring.
A decent tube amp gives less than 0,1 % harmonic distortion at 1000 CS.

Audio Precision makes excellent gear to measure and analyse distortion.
Nevertheless it is only possible to measure and predict only with limited succes how equipment sounds.

[Jim Williams]

There is measureable THD in matched push-pull tube output devices. That is why negative feedback is applied to reduce it. Modern test gear like Audio Precision has residual THD at -120 db, far below these amps. It's easy to find and measure. Throw the CCIF IMD tests on them and you find other errors like slew limiting.

As I said it's really down to personal choice, I find a very fast current feedback transistor amp design reveals more than the tube/transformer designs do, at least to me. The same applies to mic amps, I prefer the transistor stuff for total accuracy, the tubes for some euphonic treatment. Each has their place.
YMMV.

[polypals]

Jim.

You missed the point I was describing a power amp with output triodes.
With paired output tubes the distortion from the output tubes is virtually zero.
That is a simple matter of mathematics.

Im refering to power amps from the golden age of American design.
Take the Harman Kardon 11 amp. The output tubes are applied half way between penthode and triode inh ultra lineair mode.
This amp uses video penthodes as drivers to assure wide band amplification. That makes NFB in multiple loops possible without risking stability of the amp. One of the best tube amps I ever listened to.

[klaus]

Please keep topics microphone-related, and whenever there is an off-topic argument to be discussed, especially one that may be  outside the interest of most microphone users, please PM each other.
Thanks.