Misleading Measurements

[bluesman]

28 minutes ago, fas42 said:

Thanks. Unfortunately, this still does not distinguish whether the difference tones, created as a real phenomenon, is caused by the air, or by some other object in the recording space ... IOW, what is the most likely candidate for reacting in a non-linear way to the vibrations of the strings, and how do we ascertain that in fact this is what happened?

My mind is open.  What kinds of objects do you think might have done this instead of actual interaction between the tones?  The ~9'x14' room contains bookshelves loaded with heavy books, a large stuffed chair, about 1500 record albums, several computers, 3 pairs of small, powered speakers plus a sub, one guitar amplifier, a Canon printer, a 15' long desk/drawer unit with counter top, and a glass coffee table.

 

Before you get too far into this, I ran the same experiment in our ~25'x30' great room and got the exact same spectrum except for the HVAC noise, which was lower in intensity because I placed the mic at the far end of the room from the HVAC unit.  That room contains a grand piano, several large pieces of furniture, another coffee table, my Focal towers, an 8 seat dining room table, and 2 wall units containing everything from china and silver to liquor bottles.

 

From where I sit, trying to pin this on random inanimate objects looks a lot like this:  

[bluesman]

15 minutes ago, pkane2001 said:

Here's an example of this non-linearity causing harmonic distortion (which is the same as IMD, except measured with a single tone, as we discussed already).

I don't think that's correct.  From the Linear Circuit Design Handbook (2008) by Hank Zumbahlen, harmonic distortion is defined as the ratio of harmonics to fundamental when a (theoretically) pure sinewave is reconstructed.  Intermodulation products are not harmonics of the tones that produce them, but harmonic distortion products are.  So HD tones can be identified as multiples of the fundamental frequency producing them, while IM tones can be identified by their relationships to the tones that produce them (sum & difference frequencies).

[Audiophile Neuroscience]

16 minutes ago, bluesman said:

From where I sit, trying to pin this on random inanimate objects looks a lot like this:  

Frank's specialty 😄

[pkane2001]

40 minutes ago, bluesman said:

I don't think that's correct.  From the Linear Circuit Design Handbook (2008) by Hank Zumbahlen, harmonic distortion is defined as the ratio of harmonics to fundamental when a (theoretically) pure sinewave is reconstructed.  Intermodulation products are not harmonics of the tones that produce them, but harmonic distortion products are.  So HD tones can be identified as multiples of the fundamental frequency producing them, while IM tones can be identified by their relationships to the tones that produce them (sum & difference frequencies).

 

I'll repeat this one more time:  HD and IMD are both the result of exactly the same non-linearity. HD is measured with a single tone, IMD with multiple. The cause of both is the same. 

 

Here's an example. The same exact nonlinearity applied to a single tone and two tone signals using DISTORT app. This is HD:

 

Two tone signal (5kHz and 5.5kHz) going through the same exact non-linearity. Notice the IMD components:

 

Here are the two tones without non-linearity:

 

 

 

[bluesman]

31 minutes ago, pkane2001 said:

The same exact nonlinearity applied to a single tone and two tone signals using DISTORT app.

I cannot find any specifics on your website or your forum (or thread or whatever it is) on ASR.  What exactly is this magical nonlinearity on which you’re hanging all your hats?  Where and how is it applied to the signal?  How have you validated the stated effects of your app?
 

Without validation, there’s no way for us to know that it does what you say it does.  I can’t identify any mathematical model for production of a set of true harmonic frequencies from a single tone but a totally different set of nonharmonic frequencies from two.

[pkane2001]

39 minutes ago, bluesman said:

I cannot find any specifics on your website or your forum (or thread or whatever it is) on ASR.  What exactly is this magical nonlinearity on which you’re hanging all your hats?  Where and how is it applied to the signal?  How have you validated the stated effects of your app?
 

Without validation, there’s no way for us to know that it does what you say it does.  I can’t identify any mathematical model for production of a set of true harmonic frequencies from a single tone but a totally different set of nonharmonic frequencies from two.

 

DISTORT applies a non-linear transfer function to any desired signal. This is a simple mathematical operation. The result is measured using a spectral plot. You can confirm that it generates correct IMD frequencies with two or more tones, as these are easily verifiable by comparing the result with any text on IMD by specifying the same frequencies/amplitudes in DISTORT, or by calculating various sums and differences yourself.

 

I suggest you do some searching and reading before posting more theories on what IM is or isn't, as this topic does not require speculation. Here's the first thing I found when searching. An Analog Devices Op Amp tutorial that discusses IMD. To quote a couple of relevant paragraphs (highlights are mine):

 

Quote

INTERMODULATION DISTORTION (IMD)

When a spectrally pure sinewave passes through an amplifier (or other active device), various harmonic distortion products are produced depending upon the nature and the severity of the non-linearity. However, simply measuring harmonic distortion produced by single tone sinewaves of various frequencies does not give all the information required to evaluate the amplifier's potential performance in a communications application. [...] It is often required that an amplifier be rated in terms of the intermodulation distortion (IMD) produced with two or more specified tones applied.

 

Intermodulation distortion products are of special interest in the IF and RF area, and a major concern in the design of radio receivers. Rather than simply examining the harmonic distortion or total harmonic distortion (THD) produced by a single tone sinewave input, it is often required to look at the distortion products produced by two tones.

 

 

 

[fas42]

1 hour ago, bluesman said:

From where I sit, trying to pin this on random inanimate objects looks a lot like this:  

 

Hmmm, I wasn't aware that air was a live, breathing thing - will have to check that one out ...

[fas42]

Well, might have to go back to basics here, http://superior.lakeheadschools.ca/scvi_staff/childs/web-SPH3U1/downloadable_content/unit-8-Waves/textpdf8/phys11_8_1.pdf

 

To wit,

 

Quote

•     A    vibration    is    the    cyclical    motion    of    an    object    about    an    equilibrium    point.
•     All    vibrations    need    a    medium    to    transfer    waves.
•     A    mechanical    wave    is    a    transfer    of    energy    through    a    medium    by    particle
vibration. Particle vibration is caused by a disturbance to the medium.
•     A    medium    is    a    material    that    permits    the    transmission    of    energy    due    to
vibrations. A medium can be a solid, a liquid, or a gas.
•     The    particles    of    an    elastic    medium    return    to    their    original    location    after    a
wave passes through

 

Now, last time I checked, air was a gas.

 

Next step, which isn't in that document, is that non-linearity of the medium reacting to the energy exciting it is what creates difference tones; intermodulation.

 

Now, it's well documented in plenty of literature, that air is linear in its behaviour, unless extreme pressures are involved.

 

Therefore, ...

[pkane2001]

1 hour ago, bluesman said:

I cannot find any specifics on your website or your forum (or thread or whatever it is) on ASR.  What exactly is this magical nonlinearity on which you’re hanging all your hats?  Where and how is it applied to the signal?  How have you validated the stated effects of your app?
 

Without validation, there’s no way for us to know that it does what you say it does.  I can’t identify any mathematical model for production of a set of true harmonic frequencies from a single tone but a totally different set of nonharmonic frequencies from two.

 

Here's a DISTORT simulation of IMD with two tones:

 

Here's a published plot of what IMD might look like with two tones and some (unknown) non-linearity and how to compute corresponding frequencies. Notice any similarity? 

 

And since you wanted to validate what DISTORT does, here are the frequencies. Please verify against the above calculations. Note that 507Hz on the very left is actually 500Hz, but the screen resolution is too low in the lower frequencies to point to the exact Hz. The rest of the frequencies are spot-on, as far as I can tell.

 

 

[Audiophile Neuroscience]

1 hour ago, pkane2001 said:

2 hours ago, bluesman said:

I cannot find any specifics on your website or your forum (or thread or whatever it is) on ASR.  What exactly is this magical nonlinearity on which you’re hanging all your hats?  Where and how is it applied to the signal?  How have you validated the stated effects of your app?
 

Without validation, there’s no way for us to know that it does what you say it does.  I can’t identify any mathematical model for production of a set of true harmonic frequencies from a single tone but a totally different set of nonharmonic frequencies from two.

Read more  

 

Here's a DISTORT simulation of IMD with two tones:

 

Here's a published plot of what IMD might look like with two tones and some (unknown) non-linearity and how to compute corresponding frequencies. Notice any similarity? 

 

And since you wanted to validate what DISTORT does, here are the frequencies. Please verify against the above calculations. Note that 507Hz on the very left is actually 500Hz, but the screen resolution is too low in the lower frequencies to point to the exact Hz. The rest of the frequencies are spot-on, as far as I can tell.

 

 

 

The issue of validating the tool being used is a legitimate question just as it is for blind listening tests or any other measuring tool - the test of the test parameters eg published sensitivity,specificity, reliability etc. If you cannot produce these numbers in relation to a gold standard reference (and I am not saying you can't) then your tool is not validated.

 

The comparison images you present are IMO hardly convincing without knowing more about the legitimacy of the reference to which you rely. It should be an established gold standard. It does not inspire me thus far to know the reference source is some guy on a blog selling stuff who lists his credentials as

 

"I began posting training videos on YouTube to help teach the volunteer sound team at my church how to learn the sound board. What I didn’t see coming was that God had a much larger plan!

Videos that were intended for only a handful of volunteers have been viewed roughly 4 million times!

I want to do everything in my power to help churches succeed and their volunteers find confidence. Here are 6 ways you can access my knowledge and experience. I have arranged these in order, from those that require the least investment to those that require the most.

1. Search my site. I am continually putting out new posts and content on how to master your audio console. Simply use the search bar in the upper right corner to get started.

2. Subscribe to my updates. By subscribing, you’ll get a notification when I post something new and additional content that I haven’t posted publicly. Learn more…

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4. Buy one of my products. You can find them in the store. I created these products and resources to simplify and help speed up your workflows. I have several other products in development, so stay tuned! Learn more…

5. Work with me on Skype. I have limited availability for 1-on-1 online training & consulting. This is a great option if you have questions on a setup that is complicated and specific. Skype trainings are booked on a per-hour basis. Contact my team to get it set up.

6. Hire me for in-person training. I love working with large teams, face to face, setting up the board and training everyone all at once! Due to the time required, the costs associated with this option are typically very high. If you feel that your team can benefit from a 2 day training, contact my team for more information.

[pkane2001]

3 hours ago, Audiophile Neuroscience said:

 

The issue of validating the tool being used is a legitimate question just as it is for blind listening tests or any other measuring tool - the test of the test parameters eg published sensitivity,specificity, reliability etc. If you cannot produce these numbers in relation to a gold standard reference (and I am not saying you can't) then your tool is not validated.

 

The comparison images you present are IMO hardly convincing without knowing more about the legitimacy of the reference to which you rely. It should be an established gold standard. It does not inspire me thus far to know the reference source is some guy on a blog selling stuff who lists his credentials as

 

"I began posting training videos on YouTube to help teach the volunteer sound team at my church how to learn the sound board. What I didn’t see coming was that God had a much larger plan!

Videos that were intended for only a handful of volunteers have been viewed roughly 4 million times!

I want to do everything in my power to help churches succeed and their volunteers find confidence. Here are 6 ways you can access my knowledge and experience. I have arranged these in order, from those that require the least investment to those that require the most.

1. Search my site. I am continually putting out new posts and content on how to master your audio console. Simply use the search bar in the upper right corner to get started.

2. Subscribe to my updates. By subscribing, you’ll get a notification when I post something new and additional content that I haven’t posted publicly. Learn more…

3. Subscribe on YouTube. If you’re a visual learner, you’ll want to subscribe on Youtube for access to over 100 videos and updates on new training. Learn more…

4. Buy one of my products. You can find them in the store. I created these products and resources to simplify and help speed up your workflows. I have several other products in development, so stay tuned! Learn more…

5. Work with me on Skype. I have limited availability for 1-on-1 online training & consulting. This is a great option if you have questions on a setup that is complicated and specific. Skype trainings are booked on a per-hour basis. Contact my team to get it set up.

6. Hire me for in-person training. I love working with large teams, face to face, setting up the board and training everyone all at once! Due to the time required, the costs associated with this option are typically very high. If you feel that your team can benefit from a 2 day training, contact my team for more information.

DISTORT has been validated, and not just by me. It’s impossible to validate a tool without first understanding of what it does. Once you do understand, the validation becomes extremely obvious. 
 

So, what would you like to see validated?

 

 

[Audiophile Neuroscience]

12 minutes ago, pkane2001 said:

DISTORT has been validated, and not just by me. It’s impossible to validate a tool without first understanding of what it does. Once you do understand, the validation becomes extremely obvious. 
 

So, what would you like to see validated?

 

 

 

A good start would be offering what validation you have. I don't buy 'you wouldn't understand it'. I don't have to necessarily understand all the the technical details depending on how the validation is offered. If a recognized certifying body says it tested the tool and it does what it says on the can, that is one way. Independent publications where the tool is calibrated against a known gold standard is another, if you know for example what is the sensitivity of the tool, quote it - most everyone understands this.

The point is, if you are offering a tool to persuade someone of something,one likes to know if it does what it purports to do.I am not saying your app does not do that. @bluesman asked a question about validation to which I think deserves a reply.

[pkane2001]

21 minutes ago, Audiophile Neuroscience said:

 

A good start would be offering what validation you have. I don't buy 'you wouldn't understand it'. I don't have to necessarily understand all the the technical details depending on how the validation is offered. If a recognized certifying body says it tested the tool and it does what it says on the can, that is one way. Independent publications where the tool is calibrated against a known gold standard is another, if you know for example what is the sensitivity of the tool, quote it - most everyone understands this.

The point is, if you are offering a tool to persuade someone of something,one likes to know if it does what it purports to do.I am not saying your app does not do that. @bluesman asked a question about validation to which I think deserves a reply.

Again, easy to do for anyone interested, and I already replied.
 

It’s up to you or bluesman to understand why my reply was a proper way to validate the tool. You can find an explanation of what IMD is and what frequencies it produces in any basic text on distortion. That chart I linked was a proper example of IMD frequencies, regardless of who posted it, showing the math details. It’s  curious that you’d attack the person who shared it without first asking if the information he shared was accurate. 
 

I’m not here to teach signal distortion analysis, it’s been done a million times, look it up if interested. Many tutorials, textbooks and papers and blogs published on the subject.
 

DISTORT is easy to validate, like any other device that produces distortions: feed it a desired test signal, measure the output and confirm that the expected distortion was added through analysis. No magic, and you can chose your own tools to do the analysis, since you don’t trust mine.

[Audiophile Neuroscience]

16 minutes ago, pkane2001 said:

DISTORT is easy to validate

apparently not

[pkane2001]

13 minutes ago, Audiophile Neuroscience said:

apparently not

 

Some basic understanding is required. No getting around that fact.

[Audiophile Neuroscience]

4 minutes ago, pkane2001 said:

 

Some basic understanding is required. No getting around that fact.

 

I agree 🙄

[bluesman]

8 hours ago, pkane2001 said:

When a spectrally pure sinewave passes through an amplifier (or other active device), various harmonic distortion products are produced depending upon the nature and the severity of the non-linearity.

I’m probably more knowledgeable about this than you think I am.  And I think you may have bonded the wrong content - so I fixed it for you.  The last phrase is the exact reason I asked you to tell us what you’re doing to the signal, along with how and where in the path between input & output  The nature of the signal manipulation is critical to knowing exact what effect it’s likely to have.  
 

I also note with interest that I got the same IM products just mixing two tones that you got by “treating” two tones with your app. So how would we know that your app did anything, especially if you won’t tell us what it does.

 

8 hours ago, pkane2001 said:

Intermodulation distortion products are of special interest in the IF and RF area, and a major concern in the design of radio receivers.

Absolutely.  IM products can and do directly affect radio reception directly, eg by creating side bands that suck bandwidth and even affect the SQ of reception.  And it’s not only reasonable but highly likely that they do the same thing in the audio band.  It’s the source of that IM that you continued dispute with me.

 

I did not realize that you were using your own “black box” app to support your assertions until last night.  As we’re clearly not communicating well about this, and you won’t even consider that some of your arguments might be less than 100% correct, I’ve said my piece.

 

If I’m wrong, so be it.  You simply haven’t offered a single piece of evidence or data that I am.

[bluesman]

8 hours ago, fas42 said:

Now, it's well documented in plenty of literature, that air is linear in its behaviour,

So if nonlinearity causes IM and you agree that air is linear in its behavior, why do you think that it’s the “source” of IM products?

[Audiophile Neuroscience]

7 minutes ago, bluesman said:

I did not realize that you were using your own “black box” app to support your assertions until last night.  As we’re clearly not communicating well about this, and you won’t even consider that some of your arguments might be less than 100% correct, I’ve said my piece.

But it is up to you to validate Paul's app 😄

[pkane2001]

1 minute ago, bluesman said:

I’m probably more knowledgeable about this than you think I am.  And I think you may have bonded the wrong content - so I fixed it for you.  The last phrase is the exact reason I asked you to tell us what you’re doing to the signal, along with how and where in the path between input & output  The nature of the signal manipulation is critical to knowing exact what effect it’s likely to have.  
 

I also note with interest that I got the same IM products just mixing two tones that you got by “treating” two tones with your app. So how would we know that your app did anything, especially if you won’t tell us what it does.

 

Absolutely.  IM products can and do directly affect radio reception directly, eg by creating side bands that suck bandwidth and even affect the SQ of reception.  And it’s not only reasonable but highly likely that they do the same thing in the audio band.  It’s the source of that IM that you continued dispute with me.

 

I did not realize that you were using your own “black box” app to support your assertions until last night.  As we’re clearly not communicating well about this, and you won’t even consider that some of your arguments might be less than 100% correct, I’ve said my piece.

 

If I’m wrong, so be it.  You simply haven’t offered a single piece of evidence or data that I am.

 

Between the input and the output is f(x) where f is a non-linear function. Is that clear enough? That's a definition of non-linearity. X is the signal in, f(x) is the signal out.

 

There are no additional tones being individually added, or any frequency domain manipulation in DISTORT when applying non-linearity. It works exactly like any non-linear analog device would, by changing the transfer function, except that it's done using calculations rather than hardware. f(x) is then measured using spectrum/FFT and other analysis tools. You can output f(x) result to a digital file or to a sound device driver and then analyze it using whatever other tools you want. REW is the one I often use. APx500 software that Chris is looking into would also work. Or even my own DeltaWave. As I said, no magic. Simple non-linear distortion causing HD and IMD.

[bluesman]

2 hours ago, pkane2001 said:

 

Some basic understanding is required. No getting around that fact.

If, as you seem to be suggesting with your “demonstration” above, the same nonlinearity produces both harmonic and intermodulation products, how in the world could you use it to add only one or the other (as you suggest can be done with your app)?

 

[pkane2001]

9 minutes ago, bluesman said:

If, as you seem to be suggesting with your “demonstration” above, the same nonlinearity produces both harmonic and intermodulation products, how in the world could you use it to add only one or the other (as you suggest can be done with your app)?

 

Sorry, but if you keep ignoring what I write, then this whole conversation is pointless. HD is generated with a single sine wave test signal, the x in f(x), IMD with multiple tones. DISTORT lets you pick your test signal, or even feed your own, so you don't have to depend on it to generate it. You can read the test signal setting in the screen captures, All the settings, including the test signal used, are listed in the panel on the left.

 

Here's that same non-linearity applied to a 32-tone signal:

 

 

 

[bluesman]

3 minutes ago, pkane2001 said:

Between the input and the output is f(x) where f is a non-linear function. Is that clear enough?

It’s not nearly enough.  Y=X squared is a nonlinear function. Maybe that’s what your app does.

[Audiophile Neuroscience]

9 minutes ago, pkane2001 said:

You can read the test signal setting in the screen captures, All the settings, including the test signal used, are listed in the panel on the left.

 

so long as settings are listed in the panel on the left, all good !

[pkane2001]

1 minute ago, bluesman said:

It’s not nearly enough.  Y=X squared is a nonlinear function. Maybe that’s what your app does.

 

It really doesn't matter. Nonlinearity of all kinds causes the same effect. My app allows you to create infinite number non-linearities, and in fact, even simulate those of real devices. And you can verify that it's doing it by applying a test signal to input and measuring the output.