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In Reply to: Boyk and Cheever papers shot down... posted by theaudiohobby on March 18, 2007 at 18:42:09:
I have just spent about 10 minutes skimming a report by Boyk and Sussman called 'small-signal distortion in feedback amplifiers for audio' which is not a paper for a techncial journal but looks more like a class project report. Is this the Boyk paper?Obviously I have not checked the details but the results do not look wrong in a way that would trigger one to check and they are reported in a reasonably correct manner. The authors would seem to want the results to support what looks a bit like audiophile beliefs but they are honest enough about what is and is not supported. They do add some doubtful looking speculation but they are honest and call it speculation. Personally, I can see nothing wrong with this report but please feel free to draw my attention to things I have missed.
The Cheever thesis is something else entirely.
I am curious why you feel the papers need shooting down. If you wish to convert audiophiles to the one true path to truth and enlightment do you think they will be swayed by the opposition having a low opinion of what serves to bolster their beliefs?
Follow Ups:
"I have just spent about 10 minutes skimming a report by Boyk and Sussman called 'small-signal distortion in feedback amplifiers for audio' which is not a paper for a techncial journal but looks more like a class project report. Is this the Boyk paper"
Yes, this is what I was referring to as the Boyk paper."I am curious why you feel the papers need shooting down. If you wish to convert audiophiles to the one true path to truth and enlightment do you think they will be swayed by the opposition having a low opinion of what serves to bolster their beliefs?"
The answer to your question is No, Many folks, in this instance audiophiles simply get defensive when confronted with information that runs contrary to their beliefs even when the contrary information is valid and this behaviour is not unique to this hobby. I am pleased that the information in both publications have been scrutinised in the context of existing information on the subject and have been found lacking i.e. the models and some of the key assumptions that form the basis of each of these publications are not applicable real-world devices, which renders them redundant as a valid citations to support reasonable discussions on amplifier distortion, I say reasonable become some folks will simply wave off the valid criticism leveled against both papers and cite them anyway.
Music making the painting, recording it the photograph
> I am pleased that the information in both publications have been
> scrutinised in the context of existing information on the subject and
> have been found lacking i.e. the models and some of the key
> assumptions that form the basis of each of these publications are not
> applicable real-world devices, which renders them redundant as a valid
> citations to support reasonable discussions on amplifier distortion, I
> say reasonable become some folks will simply wave off the valid
> criticism leveled against both papers and cite them anyway.Now the Cheever thesis can and should be condemned for a failure to follow the scientific method. But if much of the work was copied from Baxandall how can the Baxandall work be used to shoot it down? I am not saying it cannot simply that it seems odd.
The Boyk report would seem to be the complete opposite. Here is a music lecturer with, presumably, audiophile beliefs who roles up his sleeves and does some work to show how his expectations map to the scientific domain with some help from an Electrical Engineering prof. The presented work is clear, easy to follow and not distorted in any immediately obvious way. Yes there is some wishful thinking along audiophile lines and some laziness in speculating on psychoacoustic outcomes without taking the small amount of time to look them up but the results look perfectly reasonable and do not seem to support audiophile beliefs in any form I recognise.
If one shoots down the Cheever work on grounds of unscientific work surely one must support the Boyk work for the same reason?
As far as real world devices are concerned the Boyk work is quite clear about what is compared, how and why. To shoot it down for something it does not claim to be seems unreasonable and has strong echoes of audiophile behaviour. To shoot it down because the details are incorrect is another matter but are the details incorrect?
"As far as real world devices are concerned the Boyk work is quite clear about what is compared, how and why. To shoot it down for something it does not claim to be seems unreasonable and has strong echoes of audiophile behaviour. To shoot it down because the details are incorrect is another matter but are the details incorrect?"Hmmm you are going off on a tangent, I said
"the models and some of the key assumptions that form the basis of each of these publications are not applicable real-world devices"
The issue of whether the scientific method is adopted by both papers or not is tangential to my point. If the model or the key assumptions that underscore a given model are invalid, how can the theory formed on the basis of the said model be valid?
> Hmmm you are going off on a tangent,Not wholly. You are lumping together and shooting down what appears to me to be two very different pieces of work which piqued my interest.
> The issue of whether the scientific method is adopted by both papers
> or not is tangential to my point.OK if you say so.
> If the model or the key assumptions that underscore a given model
> are invalid, how can the theory formed on the basis of the said
> model be valid?Obviously it cannot. But the question still remains: what is wrong with the Boyk models which on a quick scan seem reasonable, simple and straightforward to me. Obviously there are further effects that might be introduced into the models to bring them closer to that for real devices but it is not clear that will change anything significant in the analysis. Does Baxandall or somebody else claim that something important is missing and, if so, what?
The results show feedback is feedback and not much else of significance that I can see. Boyk speculates but does not claim anything outrageous. Probably dented his audiophile beliefs a bit but they still seem to be around to flavour the introduction and conclusions. Do audiophiles really cite this report in support of the evilness of feedback or some similar audiophile belief?
"the models and some of the key assumptions that form the basis of each of these publications are not applicable real-world devices"Which would those be? The model a single ended case, a complementary case (used by nearly all transistor amps and many tube amps), and a differential stage (also used by many amps both SS and tube). Seems pretty real-world to me. It is clear from the literature that for at least BJT and triode the models are complete. For FETs there seems to be a small deviation from a quadratic behavior but as John Curl pointed out it appears that the deviation varies from FET to FET. There is no discrepancy with Baxandall in terms of calculating the harmonics, except that Boyk and Sussmann are doing a more throrough job with the help of modern computers. The discrepancy is in the interpretation of what those numbers mean psychoacoustically.
This is the major issue most have with Cheever. His claims about the Aural harmonics and masking are more controversial than this much simpler but not incorrect treatment of how the harmonics are generated. If he did lift this from Baxandall (it is entirely possible he never saw the Baxandall stuff as it is way before his time and not so readily available perhaps. It is possible he derived it on his own) then where is the discrepancy with Baxandall??
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