Mpp

[john curl]

Today I heard the difference between two IC op amps in a phono stage. The AD797, and the OPA611. The 797 won out, but I could hope for better, if it ever comes.

[Joachim Gerhard]

I am just testing this :
http://www.analog.com/static/importe...8-1_4898-2.pdf
it has a very low 1/F corner frequency but there seen to be issues with the feedback resistor.
The AD797 is the best low noise chip i know so far. In the right circuit it is hard to measure distortion, belcher test and noise modulation included.

[Joachim Gerhard]

What is OPA611 ?
If it is the OPA211 then the AD797 is better. Much better driving ability and slightly lower noise. I did not try the OPA1611 though. It´s on the way.

[scott wurcer]

Originally Posted by Joachim Gerhard

Sound Intensity

That refers to single frequency threshold. I have been 30mi from everything in the northern woods myself (@-30F) and in an anechoic chamber and I still feel the circulatory system accounted for all the low frequency "rushing' noise. Here is an interesting reference but I'm not about to spend $31.50 to satisfy curiosity.


The influence of stochastic behavior on the human threshold of hearing

References and further reading may be available for this article. To view references and further reading you must purchase this article.


Ilse Christine Gebeshubera, b, ,

aTU-BioMed, University of Technology, Wiedner Hauptstr. 8-10/1145, A-1040 Vienna, Austria

bPhysics Department, University of California, Santa Barbara, CA 93106, USA

[john curl]

OPA1611 it is. Noise difference is not significant. Sound difference is perplexing. If I could, I would use the OPA1611, it is effectively just as quiet, much cheaper to buy, and has a slightly higher open loop bandwidth.

[Joachim Gerhard]

Ok, i will go more deep into it and will be better prepared to answer.
What researchers at Würzburg told me is that the ear sensitivity goes up by 40dB if a short
high frequency pulse hits the ears so there is some diferentiation of the input signal going on. They measured the nerve firing rate with high frequency pulse input. To avoid impulse disturbance from the loudspeaker they used Manger Transducers (MSW) in a kind of big headphone arangement.
Tomorrow i will call Daniela Manger for more information.
This thread get´s hard work !

[john curl]

You know Daniela Manger? I know both her, and I first met her father in 1975. Great engineers.

[brianco]

Originally Posted by scott wurcer

.............. I have been 30mi from everything in the northern woods myself (@-30F) and in an anechoic chamber and I still feel the circulatory system accounted for all the low frequency "rushing' noise. ...............................

I live in deeper countryside and often hear the passage of blood in/around my ears; most often in the early morning should I wake from sleep unexpectedly. It is not the same as that deepest silence of truly remote locations in still-air conditions when the silence is deafening. At times I also fish in very remote areas and am now well used to the experience! [It can also create unexpected emotional response.]

My own experience is that when either sound or vision reception has no external reference of any sort that one becomes disorientated. Walk deep into a photographers infinity vision chamber - I've forgotten the proper name - and one's whole sense of physical balance and even existence appears threatened. Having seen six sheep being photographed in the total whiteness of this chamber - which is an inverted half oblate spheroid with a totally matt-white finish... it was obvious that they were very distressed indeed by the altered visual context. [They had refused to enter and had to be carried in. Once on their feet again they refused to move and had to be manually placed in position.]

If an object is placed at the correct point in this chamber it visually appears to float. The lighting is such that no shadows are thrown, and there is simply no line or point of visual reference. I have also been in an anechoic chamber, and I imagine that if all visual stimulus were also removed one would would go quite mad in a short period of time!

The point of these observations is that they show, me at least, that a real time reference is a requirement for any form of normal visual or sound experience to be valid.

[scott wurcer]

Originally Posted by brianco

My own experience is that when either sound or vision reception has no external reference of any sort that one becomes disorientated. Walk deep into a photographers infinity vision chamber - I've forgotten the proper name - and one's whole sense of physical balance and even existence appears threatened.

We used to walk about 1/2 a mi into the storm drain system to get total sensory deprivation. I understand the feeling. I still think the brain is reacting to the confusion and it is not simply the "noise floor". Ikoflexer sent me a link to that paper on how stocastic resonance figures into this. This is clearly beyond a casual discussion of anecdotal experiences.

[Salas]

Originally Posted by brianco

The point of these observations is that they show, me at least, that a real time reference is a requirement for any form of normal visual or sound experience to be valid.

Heard that! Says DBT.