Hello Amir,
Thank you for your great comments. We worked directly with Dr. Earl Geddes during the implementation of the GedLee Metric into MI Pro. I had corresponded with Earl at the time about his thoughts on NCD vs. that of Gm distortion and he opined that perhaps NCD would prove to be more relevant (but that of course needs to be tested out in a properly run double-blind psychoacoustic study IMO).
Since there has never been a GedLee Metric analyzer ever made (now there is one with MI Pro) it remains to be seen via such aforementioned studies how Gm distortion compares to NCD vs. that of THD and IMD.
I would love to get your thoughts on NCD which MI Pro also does, since NCD has some some well documented empirical research published in the AES by Dr. Sean Olive of Harman and Steve Temme of Listen, Inc. showing in double-blind studies how it was the only objective measurement of audio distortion that correlated with subjective listeners perceptions whereas THD and IMD had no such correlation. Please see the following:
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https://bit.ly/2ITRmCG (AES PDF document)
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https://bit.ly/2IZvDFe (YouTube AES presentation by Dr. Sean Olive and Steve Temme this topic)
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https://bit.ly/2LIhOgc (AES paper...sorry, I can't provide it since it is copyrighted & sold via the AES)
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https://bit.ly/2LaJZ6x (MI Pro PDF manual, please do a quick Adobe PDF key word search for "GedLee" and for "NCD")
So it may well be that Gm distortion is not as relevant as NCD, but again, I would like to get your thoughts / comments on NCD and of NCD vs. THD and IMD too please, (I've always enjoyed reading your exceptionally well researched postings
).
Virtins is now considering, but it not (yet) guaranteed, to incorporate yet another psychoacoustically based objective measure of distortion into MI Pro that Dolby Labs had invented. You can read about this model by reading the below AES paper:
Perceptual Assessment of Headphone Distortion, by Louis D. Fielder, Dolby Labs, AES paper, Oct 2017
Again, it has *not* been firmly decided to incorporate the above into MI Pro, but it appears to be likely, (and if it is incorporated into MI Pro, it would be a 100% free upgrade to all existing MI Pro owners too, i.e., no extra cost).
Please note too that the new headphone / IEM measurement guru (Keith Howard) at the very well known / respected website InnerFidelity will start to measure all future reviewed headphones and IEMs not only with THD and IMD but with NCD and Gm distortion as well, please see:
https://bit.ly/2xsQ5gl And since MI Pro is the only audio analyzer in the world with Gm distortion capabilities, you know which software he'll be using
I think the whole field of audio distortion testing is ripe for a lot more research. Up to now, 99.99% of all the world's audio analyzers only offered THD and IMD but IMO, the audio community at large has to move into doing research and using more relevant objective measures of audio distortion. Now that we have MI Pro with these more advanced ways of measuring distortion, and at such a low cost vs. some of the competition, it is high time for researchers to conduct such studies IMO.
Finally, in answer to your question on cost, the cost of the RTX6001 itself is now ~$2,500 USD plus shipping cost from Europe of between $50 to $100 USD. The cost of MI Pro as part of this GB I hope (depends on # of MI Pro GB who sign up for GB) will end up being $190 USD with free worldwide express shipping of the USB protection dongle. In reality, this is *NOT* a GB discounted price for the RTX6001, it is only a GB discounted price for MI Pro as well as MI add-on modules that are only discounted during this GB special. I suspect a lot of people joining this MI Pro GB will *NOT* own an RTX6001, but most will be using high quality sound cards with MI Pro instead.
Having said the above, the MI Pro GB is not by any means only a great value for RTX6001 owners, (the cost of the RTX6001 [not MI Pro] is a lot of $$$ to pay, but once the custom API for MI Pro is done, making the RTX6001 into a fully capable autoranging / autoscaling audio analyzer it is still less $$$ than other brand new pro class audio analyzers with such functionality IMO, e.g., AP, dScope, etc.).
It is very important to note that MI Pro works with ones' typical sound card to convert it into a high quality audio analyzer too. Sure, if one wants to pay the $$$ to get AP / dScope like professional class results, one can buy an RTX6001 too with the custom API to have it's internal attenuators and gains remotely controlled via the MI Pro software, but most GB MI Pro users will probably not opt to go that route, but instead just buy MI Pro and use it with a sound card much like ARTA, REW, SpectraPLUS-SC, etc.
Thank you again for your great comments and looking forward to hearing back from you on the questions I've asked for your opinions on above. Have a great day!
V/R,
MI Pro