Audio measurement gear

[restorer-john]

That's insanely good. Thank you so much for doing those real world tests. As you say, it's an absolute bargain.

I had considered a lovely R&S analzyer, but combine an ancient interface and a small LCD, I couldn't do it. Even my old AudioLab was PC based in 1995 and it's still going.

The only other question I am wondering is USB power. Clearly it has internal supplies, but with all the talk here on USB power issues/noise (schiit etc), I wonder if there's situations where some PCs/Laptops will be better than others in terms of the USB power delivery. Are you running a powered hub for it as the unit mentions USB power on the top. A USB 3.0 port surely would have decent enough power for it. I wanted to use some older Stinkpads which are nice 15" 4:3 dual cores (easier on my eyes) and they are USB 2.0.

I think I'll order mine in a few weeks.

 

[March Audio]

The 401 does indeed have its own supplies and is isolated however in their blog QA do comment on how noise can still get in.

https://quantasylum.com/blogs/news/qa401-and-usb-noise

Also it does use about 600mA which in theory exceeds the usb2 spec, but is OK with usb 3 which is good for 900mA IIRC. However you can simply use a powered hub if there are issues

 

[restorer-john]

In my case, where I want to run old laptop computers with USB 2.0 ports, I can either parallel the ports (like the old USB HDD connectors) or run a 5.0v 2.0A hub PSU to feed it. Mostly, I think the main PC on my bench (USB 3.0) will be the workhorse.

Thanks again for your insight.

John

 

[mi pro]

Hello Everyone,

I have posted a Group Buy (GB) announcement for audio analyzer software that does the following:

- Traditional, old fashioned, and non-relevant (IMO) THD and IMD, but far more importantly, the vastly more modern and relevant non-coherent distortion (NCD) as well as the Dr. Earl Geddes "GedLee Metric" (Gm distortion).

- If you own an RTX6001 audio analyzer this software has a custom API that controls the RTX's internal attenuators and gains to allow for true autoranging and autoscaling (which is a HUGE deal).

- Even if you don't own an RTX6001 and instead use a soundcard type of approach, the new distortion and other features of this software will prove to be very useful to many IMO.

You can read more about this GB audio analyzer software at: https://bit.ly/2LdMtB9

Please note that in the GB I cite a couple of excellent postings from this forum's founder as well, (he was too spot on IMO not to cite him )

 

[SIY]

I've used Virtins MI software in conjunction with sound cards (write-up was in AudioXpress, March 2016) and though rather difficult to learn, it's amazingly powerful, worth every penny. Looking forward to seeing the latest and greatest from you!

 

[mi pro]

I've used Virtins MI software in conjunction with sound cards (write-up was in AudioXpress, March 2016) and though rather difficult to learn, it's amazingly powerful, worth every penny. Looking forward to seeing the latest and greatest from you!

Thank you very much for your very positive comments! Yes, MI Pro, like any powerful audio analyzer, has a learning curve associated with its use. I like the comments made in posting # 11 (CharlieLaub) and especially # 12 (1audio), # 13 (jan.didden) and # 14 (again, "1audio") that sums up this idea very nicely IMO, see: https://bit.ly/2Ha2hlP

By the way, I have read the wonderful articles you've coined in AudioXpress Stuart, so please keep them coming

 

[SIY]

Many thanks for the kind words. I should add that, unlike some other software I've used (cough, cough, Audiotester), the MI is absolutely stable and crash-free on my computer.

Just for clarity, 1audio is Demien Martin, a very skilled and experienced engineer.

 

[amirm]

Hello Everyone,

I have posted a Group Buy (GB) announcement for audio analyzer software that does the following:

I tried to read through your post on DIY forum but got lost. So what is the total cost of hardware and software for this group buy?

 

[mi pro]

Hello again Stuart,

Yes, I wholeheartedly agree with your comments that Demien Martin (1audio) is a very skilled, exceptionally knowledgeable, and superbly talented engineer. I have followed many of his postings on the diyaudio website throughout the years and he never fails to impress me.

I also have a high regard for Charlie and Jan that I cited above too. The point I was attempting to get across is that any powerful / professional grade audio analyzer software always has a steep learning curve associated with its use. That is why proper documentation is absolutely essential IMO. The URL link I provide in posting # 116 above also shows that Demien Martin, Chrlie and Jan also have the same opinion in this respect.

If one looks at the Virtins website and all the various documentation contained therein they'll see they are not "left to figure it out on their own," e.g., the main PDF manual for MI is almost 400 pages in size for example. In addition to the impressively thorough user's manual the Virtins website also has far more such documentation that anyone can download that will assist end users of MI Pro with respect to how to get great results from it.

As with anything worthwhile, if one doesn't read the manual and other documentation and learn the interface, than obviously they won't end up understanding how to get the most out of it. IMO the same type of thing can be said for other wonderfully power audio analyzer programs too, e.g., ARTA, REW, etc.

The difference between MI Pro and these other wonderful programs for me relate to the custom API to remotely control the RTX6001 to allow for true autoranging and autoscaling as well as the far more perceptually relevant objective means of measuring audio distortion (GedLee Metric [Gm distortion] and NCD) that no other analyzers in the world have.

The psychoacoustically based GedLee Metric (Gm distortion) and NCD are the # 1 reason IMO people without an RTX6001 will want to own MI Pro and get in on the MI Pro GB (typical sound card based users...nothing inherently wrong with this approach IMO as your superbly written articles in AudioXpress make very clear). I think these newer ways of objectively measuring audio distortion, that have a high degree of correlation with how one perceives sound quality (unlike the old fashioned / outdated THD and IMD that lack such correlation) will end up being used a lot for headphone, in ear monitor (IEMs) and loudspeaker DIY'ers and researchers worldwide. I am confident that these newer more relevant ways of objectively measuring audio distortion will eventually replace THD and IMD and that audio manufacturers and standards committes will end up adopting them as well.

For RTX6001 end users, to me it is a no-brainier, i.e., if they want have their RTX6001 work in the same way as "professional class" audio analyzers (e.g., Audio Precision or Prism dScope, etc.) work, than they absolutely need the custom API that the MI Pro GB provides.

Thank you again Stuart for your supportive comments and wishing you all the very best!

V/R,

MI Pro

 

[amirm]

- Traditional, old fashioned, and non-relevant (IMO) THD and IMD, but far more importantly, the vastly more modern and relevant non-coherent distortion (NCD) as well as the Dr. Earl Geddes "GedLee Metric" (Gm distortion).

While Earl's metric is more psychoacoustically aware than THD/IMD, it is still pretty far from what we hear. And at any rate seems to be focused on higher levels of distortion than what we see in audio gear (crossover distortion example given in papers is not the the type of distortion we worry about in 99% of audio gear).

A full psychoacoustic model is needed to evaluate audibility of distortion and even those are not very accurate (although far better than Gm). And at any rate, a correct model would say vast majority of equipment we test has no audible distortion.

What we try to quantify using these measurements are whether there are engineering errors and there, the classical measures like THD/IMD are better to communicate that to the manufacturer.

 

[mi pro]

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:

- https://bit.ly/2ITRmCG (AES PDF document)

- https://bit.ly/2IZvDFe (YouTube AES presentation by Dr. Sean Olive and Steve Temme this topic)

- https://bit.ly/2LIhOgc (AES paper...sorry, I can't provide it since it is copyrighted & sold via the AES)

- 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

 

[amirm]

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!

Thanks for the kind explanation. My comments were in regards to measuring electronics. Measuring loudspeakers/headphones is an entirely different matter. There, I consider linear distortions, i.e. frequency response, to be the dominant factor in listener preference. Distortion ranks way lower than that (other than clear resonances and such which manifest themselves in frequency response variations anyway).

That said, let me spend some time reading the papers you cited and respond back.

 

[derp1n]

Is there a summary of lower cost gear suitable for audio measurements anywhere? I'm tempted to pick up a QA401, but part of me wonders if I'd be better off trying to use a RME ADI-2 Pro FS since I can use it as a real audio interface as well, whereas the QA401 is a bit too specialized (although the coming ASIO drivers might solve that).

 

[bennetng]

Is there a summary of lower cost gear suitable for audio measurements anywhere? I'm tempted to pick up a QA401, but part of me wonders if I'd be better off trying to use a RME ADI-2 Pro FS since I can use it as a real audio interface as well, whereas the QA401 is a bit too specialized (although the coming ASIO drivers might solve that).

Yes, but in Russian, the maker of RMAA.
http://prosound.ixbt.com/interfaces.html

Remember to click the link to see the detailed reports in all of the reviewed products.

 

[March Audio]

Is there a summary of lower cost gear suitable for audio measurements anywhere? I'm tempted to pick up a QA401, but part of me wonders if I'd be better off trying to use a RME ADI-2 Pro FS since I can use it as a real audio interface as well, whereas the QA401 is a bit too specialized (although the coming ASIO drivers might solve that).

I have the ASIO driver for my QA401. It certainly works with Arta and I will try it with REW. If you are interested I am selling it at an attractive price.

 

[March Audio]

I've used Virtins MI software in conjunction with sound cards (write-up was in AudioXpress, March 2016) and though rather difficult to learn, it's amazingly powerful, worth every penny. Looking forward to seeing the latest and greatest from you!

I have been looking for a software package that covers all the bases and spotted your post. Got it on demo at the moment and yes it does seem to cover everything I need. Cant figure out the block length though, its always greyed out, but it changes to appropriate values if you load one of the pre configured measurement options (such as THD).

Motu 8A in loopback

 

[Wombat]

This level of higher digital understanding and application could be high-res audio's death knell in terms of market acceptance. Plug-and-play is the answer. No problem solving ability to get product to be compatible and work out of the box. Buy a modern TV, plug it in and it works. Buy a name-brand video player/recorder and plug it in and it works. Why not digital computer audio? What is so special about it? Bloody 'audiophile' individualism, I would venture.

 

[tomelex]

The simpson is where it is (was) at.

you can buy an brand new one from simpson today, they still make them! I found out when looking for panel meters, what a surprise.

https://metersales.com/catalog/83?g...LQn1X4VpGTimSi4j1JAHR6GAA4tmaoGRoCuMcQAvD_BwE

 

[amirm]

Wow, had no idea they still were in business in the age of digital! Boy did you had bragging rights if you had one of these back in the day...

 

[March Audio]

I have been looking for a software package that covers all the bases and spotted your post. Got it on demo at the moment and yes it does seem to cover everything I need. Cant figure out the block length though, its always greyed out, but it changes to appropriate values if you load one of the pre configured measurement options (such as THD).

Motu 8A in loopback

View attachment 14322

The other very useful thing about the MI software is that it will allow me to bring visual and measurement consistency with Amir's AP measurements. Plus it can save and reload measurements so I can do comparisons to other equipment on the same graph.

Excellent!

I have just replied to myself. Isn't talking to yourself the first sign of madness?