Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: The Effects of Psychology on Evaluation
Hi Bob,
Thank you for taking the time to understand and respond to my post. Just a couple of simple replies to specific comments:
It was not my intent to say that anyone was attempting to control the content or direction of the discussions
My thoughts concerning a test amp were a bit more focused. Being able to swap driver cards with variations of the contested approaches in a stable circuit environment seemed plausible. A kind of physical implementation of your simulations. Pop in an input/driver card, listen, measure and repeat. Once the circuit is designed the rest is governed by straight forward rules. Anyways, I just saw an interesting possibility.
Yes we need to challenge conventional thought, but be prepared for the lack of interest.
I agree with your comments on NFB. I think its audible negatives are magnified by the number of things that it’s required to fix. If it’s kept simple, just nailing down operating points etc., it actually is pretty hard to hear.
I also read the comments on resistor differences, and while I’ve heard differences between resistors I don’t consider them a core driver to the fundamental sound quality, more like seasonings in a recipe. As such, their effect would be subtle (masked) in any attempt to separate and measure their effect. The real culprits in audio design are much simpler in scope and will not be solved through a fanatical quest to minimize the same mechanisms that have been already beaten to death over the years.
While many factors are not readily measured they are hearable, with the ear being far more sensitive than conventional testing. Given time audio testing will catch up to what’s being done in other industries.
I’m not really a negative person; I just created (for myself) an unrealistic expectations of this forum. I remember starting in the semiconductor industry after 16 years in audio. I was expecting to be walking into a high level of technical excellence. It was a bit more fragmented than that.
Mike.
Bob Cordell said:
Hi Bob,
Thank you for taking the time to understand and respond to my post. Just a couple of simple replies to specific comments:
It was not my intent to say that anyone was attempting to control the content or direction of the discussions
My thoughts concerning a test amp were a bit more focused. Being able to swap driver cards with variations of the contested approaches in a stable circuit environment seemed plausible. A kind of physical implementation of your simulations. Pop in an input/driver card, listen, measure and repeat. Once the circuit is designed the rest is governed by straight forward rules. Anyways, I just saw an interesting possibility.
Yes we need to challenge conventional thought, but be prepared for the lack of interest.
I agree with your comments on NFB. I think its audible negatives are magnified by the number of things that it’s required to fix. If it’s kept simple, just nailing down operating points etc., it actually is pretty hard to hear.
I also read the comments on resistor differences, and while I’ve heard differences between resistors I don’t consider them a core driver to the fundamental sound quality, more like seasonings in a recipe. As such, their effect would be subtle (masked) in any attempt to separate and measure their effect. The real culprits in audio design are much simpler in scope and will not be solved through a fanatical quest to minimize the same mechanisms that have been already beaten to death over the years.
While many factors are not readily measured they are hearable, with the ear being far more sensitive than conventional testing. Given time audio testing will catch up to what’s being done in other industries.
I’m not really a negative person; I just created (for myself) an unrealistic expectations of this forum. I remember starting in the semiconductor industry after 16 years in audio. I was expecting to be walking into a high level of technical excellence. It was a bit more fragmented than that.
Mike.
AKSA said:
Hi Hugh,
Thanks for your broadening of my basic observations. I do find it interesting that so few technical people will acknowledge or look for explanations for observations that do not fit the standard world view. Mostly such things are dismissed as irrelevant.
It is also important not to replace things that don’t really need to be replaced. This is what the drive towards mass production breeds. Such well documented advancements are difficult to dispute on the basis that they don’t sound better.
As you know from your experiences designing your amps, there are many curiosities that are real yet don’t fit to the world view. Trying to integrate them into your personal knowledge base is the challenge and what makes life interesting.
As for an answer for your question, a new way of measuring is probably the best approach. A software based version of Bob Carvers null test, only you normalize the input to the output and analyze the various levels of differences, which could be done with actual music and, as Bob has suggested, using a real load. Computers and software are coming along nicely.
Just a thought. Mike.
Re: Re: My $0.02
http://www.diyaudio.com/forums/showthread.php?postid=1411783#post1411783
Plus a pair of Totem Acoustic Model 1 Signature 4 ohm speakers.
As mentioned, I do not own any high end equipment, therefore I have to rely on participants contributions (and hosting).
Terry Demol said:
http://www.diyaudio.com/forums/showthread.php?postid=1411783#post1411783
Plus a pair of Totem Acoustic Model 1 Signature 4 ohm speakers.
As mentioned, I do not own any high end equipment, therefore I have to rely on participants contributions (and hosting).
Jan,
I emphatically agree. Self changes everything. The greater the mind, the bigger the ego, and so the intellect is enthusiastically harnessed for self-justification. This explains the ebb and flow of scientific fads.
Edmond,
Thank you for your post. But you are referring to distortion measured by a very different mode.
Distortion specs are normally given steady state, sinusoidal, constant frequency. The technology is not presently able to give such measures with real world signals. Carver is in fact nulling dynamic distortion with real music, one of the great unknowns. He is using a subtraction process between two amplifiers to isolate the error 'sound', and tweaking until it is 50-70dB below the line signal. I would suspect, but cannot verify, that the dynamical transfer function is rather different to the steady state TF, but I leave this weighty problem to those with more math inclination than me. I would suspect that identical steady state distortions between two amps do not match dynamically, and therein lies the rub.
Granted, they are all distortions, but Carver's technique uses a very much more realistic approach to tease it out, and it's very likely because of the garbled mixture of frequencies and amplitudes which constitutes music that the dynamic distortions are very different.
Mike,
Could this be the DSP approach to which you allude? Yes, I think it's coming, and I suspect that the codec jockeys might hand us the solution to this vexing measurement paradigm.
I applaud Carver's technique, I think it's highly intuitive and nicely empirical. More than that, anecdotally notwithstanding, I learn something......
Cheers,
Hugh
I emphatically agree. Self changes everything. The greater the mind, the bigger the ego, and so the intellect is enthusiastically harnessed for self-justification. This explains the ebb and flow of scientific fads.
Edmond,
Thank you for your post. But you are referring to distortion measured by a very different mode.
Distortion specs are normally given steady state, sinusoidal, constant frequency. The technology is not presently able to give such measures with real world signals. Carver is in fact nulling dynamic distortion with real music, one of the great unknowns. He is using a subtraction process between two amplifiers to isolate the error 'sound', and tweaking until it is 50-70dB below the line signal. I would suspect, but cannot verify, that the dynamical transfer function is rather different to the steady state TF, but I leave this weighty problem to those with more math inclination than me. I would suspect that identical steady state distortions between two amps do not match dynamically, and therein lies the rub.
Granted, they are all distortions, but Carver's technique uses a very much more realistic approach to tease it out, and it's very likely because of the garbled mixture of frequencies and amplitudes which constitutes music that the dynamic distortions are very different.
Mike,
Could this be the DSP approach to which you allude? Yes, I think it's coming, and I suspect that the codec jockeys might hand us the solution to this vexing measurement paradigm.
I applaud Carver's technique, I think it's highly intuitive and nicely empirical. More than that, anecdotally notwithstanding, I learn something......
Cheers,
Hugh
Hugh,
I don't know who was first on the time scale, but this subtractive method was proposed in the 1983 ADI AppNote AN-245: Instrumentation Amplifiers Solve Unusual Design Problems, by Walt Jung and Scott Wurcer (see pages 5&6 for details). The trick (and the problem) is to apply the inverse transfer function at the ouput to obtain a flat gain/phase response and to rigourously filter everithing outside the bandwith of the achieved identity in transfer functions -- otherwise phase shifts (and later, gain differences) will dominate the residual. Stuff like thermal distortion, PIM etc should be identifyable with proper trimming and sophisticated measuring techniques. With two amps, one would need to match the steady state linear part of their output impedances, together with matched simulated speaker loads, in order to see things below the differences in Zout.
I found it actually easier to duplicate the DUTs transfer function in the other leg instead of inverting it in the amp's output, which allows for somewhat easier ciruitry. As an aside, with a similar test-setup I tried to nail down "cable sound" a while ago (DUT is acable, while the REF leg consist of its trimmable equivalent LCR), which was unsuccessful, but at that time I didn't know of time domain averaging before data processing (ie FFTing of HD and IMD signals), which allows to dig some 20...30dB into the thermal noise.
- Klaus
I don't know who was first on the time scale, but this subtractive method was proposed in the 1983 ADI AppNote AN-245: Instrumentation Amplifiers Solve Unusual Design Problems, by Walt Jung and Scott Wurcer (see pages 5&6 for details). The trick (and the problem) is to apply the inverse transfer function at the ouput to obtain a flat gain/phase response and to rigourously filter everithing outside the bandwith of the achieved identity in transfer functions -- otherwise phase shifts (and later, gain differences) will dominate the residual. Stuff like thermal distortion, PIM etc should be identifyable with proper trimming and sophisticated measuring techniques. With two amps, one would need to match the steady state linear part of their output impedances, together with matched simulated speaker loads, in order to see things below the differences in Zout.
I found it actually easier to duplicate the DUTs transfer function in the other leg instead of inverting it in the amp's output, which allows for somewhat easier ciruitry. As an aside, with a similar test-setup I tried to nail down "cable sound" a while ago (DUT is acable, while the REF leg consist of its trimmable equivalent LCR), which was unsuccessful, but at that time I didn't know of time domain averaging before data processing (ie FFTing of HD and IMD signals), which allows to dig some 20...30dB into the thermal noise.
- Klaus
janneman said:
Or my personal favorite, the horse that did mathematics. There are many amusing analogies to high-end audio in that story. The horse could not actually do mathematics under double-blind conditions BTW
.
Yes John, I have experienced the problem myself... in the cable test rig. The trimmable cap in the LCR equivalent circuit was an air type radio tuner style (if that's how it's called), which is very stable and has low distortion. The diff amp was a SSM2019, running at 50dB or so. Every small accidental movement of the DUT cable (especially bending it) changed its capacitance a bit and produced a phase shift, loosing the carefully adjusted nulling.
- Klaus
- Klaus
Uh, back in 1974, at some 9yrs, I used to pull the tubes in my parent's radio, playing my first electric guitar over it
In a "let's see what happens if do this and that", not knowing how dangerous this all was, 300Volts and all...
Actually, if it's not you who deserves the credits, I bet some tube dudes did it first, say back in 1930 or so...
- Klaus
In a "let's see what happens if do this and that", not knowing how dangerous this all was, 300Volts and all...
Actually, if it's not you who deserves the credits, I bet some tube dudes did it first, say back in 1930 or so...
- Klaus
AKSA said:
Oh dear. Robert Cordell has made multiple criticisms of other peoples designs and design techniques / innovations (presumably without listening to them) throughout these threads.
As for the Dartzeel thing, that was rubbished because it was a primitive design with an obscene price tag, the existence of which was justified with a load of pseudoscientific marketing baloney - hardly evidence of any detrimental "syndrome" - just commonsense.
Some people just seem to lack the latter.
Now what was the topic of this sticky thread again??
Hi Guys, sorry I have been off the air the last couple days. There have been some very useful posts. Right now I'm tied up on business in SF and in limited internet contact. I'll try to post some replies soon. I respect you all and am not ignoring anyone. Sometimes that day job just gets in the way!
Cheers,
Bob
Cheers,
Bob
scott wurcer said:
Hi Scott,
I hope we can see each other. I'll be in the High Speed Transceiver session this morning, Session 25, Salaon 9. I'll be in Session 29 this afternoon. I'll also be here tomorrow in the High Speed Transceivers Forum. If you propose a time and place to meet, I'll try to be there. Maybe lunch today if you get this?
Cheers,
Bob
Speaking of feedback, what do y'all think of this this Martin Colloms article about feedback?
If you want a PDF copy to print out and line your parrot cage with, it's available here.
If you want a PDF copy to print out and line your parrot cage with, it's available here.