Misleading Measurements

[pkane2001]

4 minutes ago, sandyk said:

 I repeat

Neither have I seen any S/W signal generator that has distortion as low as you would require, not even the best of the Analogue generators such as the Wien Bridge Oscillators .

 

I don’t require anything, Alex. Frank explained what generates IMD. That’s all. 

[sandyk]

6 minutes ago, pkane2001 said:

I don’t require anything, Alex. Frank explained what generates IMD. That’s all. 

Everything that we do in the Analogue and Digital areas results in some degree of IMD.

 

[pkane2001]

7 minutes ago, sandyk said:

Everything that we do in the Analogue and Digital areas results in some degree of IMD.

 

And increasing bit size of the internal calculations in digital domain moves digital IMD to lower and lower levels. That’s what Frank said. Another way to reduce it is dithering.

[sandyk]

18 minutes ago, pkane2001 said:

And increasing bit size of the internal calculations in digital domain moves digital IMD to lower and lower levels. That’s what Frank said. Another way to reduce it is dithering.

And dumbing it down to playable bit rates again,  increases it again.

[bluesman]

20 hours ago, fas42 said:

Again, modulation doesn't occur "in the air" - it may in the driver, but that's a completely separate issue.

 

Using two tones, over two drivers, is in fact how high quality microphones are checked for misbehaviour - microphones are going to be orders better than speakers for distortion, so how do you measure how good the mic actually is? 🙂

 

The answer, https://www.listeninc.com/products/test-sequences/free/microphone-intermodulation-distortion-measurement/

 

That doesn't address what we're talking about at all.  The stated intent of the linked article is clear and concise:  "The purpose of this sequence is to measure the Intermodulation Distortion (IM) of a microphone." 

 

We're not talking about distortion created by a device - we're talking about natural intermodulation products among tones generated by musical instruments, and how well and completely they're captured by microphones and incorporated into recordings.  And these tones do occur "in the air", if by that you mean as audible compression waves.  

 

Here's a wav of simultaneous plucking of an A 220 and a B 246 played on the 3rd and 4th strings of one of my guitars.

220_IM_test.wav 

 

You can clearly hear the 30 Hz "difference" intermodulation product, so it's "in the air" and on the recording. It's real and not only in our brains.  I didn't bother tuning perfectly to A440, so the exact frequencies are a bit off of 220 and 246.  Here's the spectrum to show the fundamentals and the IM products:

 

I know of no way to explain the ~26 Hz tone except intermodulation.  The rest of the spectrum content is from sympathetic resonance of the other strings, which are undamped and resonating.

 

[pkane2001]

9 minutes ago, sandyk said:

And dumbing it down to playable bit rates again,  increases it again.

Maybe. But that’s still outside of what was being discussed. The error in digital is due to quantization error in the last bit. It’s small to begin with, but dithering and noise shaping reduce it even further. Now, compare that to IMD levels in an audiophile amplifier, say an SET.

[bluesman]

1 hour ago, fas42 said:

If there are intermodulation frequencies created then it's because the analogue circuitry is distorting

No it's not. Natural intermodulation products are not distortion and they're not products of nonlinear or otherwise imperfect circuitry.  See my post #580 for an audio recording that clearly demonstrates natural intermodulation, along with a spectrum analysis that shows its presence in the recording.

[fas42]

5 minutes ago, bluesman said:

That doesn't address what we're talking about at all.  The stated intent of the linked article is clear and concise:  "The purpose of this sequence is to measure the Intermodulation Distortion (IM) of a microphone." 

 

The point I was making was that the pure tones, reproduced over two separate speakers, in close proximity, could each only produce harmonics, of the specific frequency fed to each - no intermodulation products would emerge from either speaker driver. And the usefulness of the test was the knowledge that intermodulation does not then occur in the air, therefore if the microphone registered any it was due to imperfections of the mic.

 

5 minutes ago, bluesman said:

 

We're not talking about distortion created by a device - we're talking about natural intermodulation products among tones generated by musical instruments, and how well and completely they're captured by microphones and incorporated into recordings.  And these tones do occur "in the air", if by that you mean as audible compression waves.  

 

Any intermodulation products must be created by some non-linearity in other than the air, otherwise the above testing technique could not be used.

 

[fas42]

12 minutes ago, bluesman said:

No it's not. Natural intermodulation products are not distortion and they're not products of nonlinear or otherwise imperfect circuitry.  See my post #580 for an audio recording that clearly demonstrates natural intermodulation, along with a spectrum analysis that shows its presence in the recording.

 

Yes, it's there, but it was created by the instrument itself - some part of it resonated at that frequency, provoked by the plucking of the strings - it's part of its intrinsic nature, its character - not added by the vibrations in the air interacting.

[bluesman]

2 minutes ago, fas42 said:

The point I was making was that the pure tones, reproduced over two separate speakers, in close proximity, could each only produce harmonics, of the specific frequency fed to each - no intermodulation products would emerge from either speaker driver.

I never said they would.  The natural intermodulation of two tones does not happen at the speakers.  The IM tones are generated by the interaction of the two waves in the air.  They're real, audible airborne compression-rarefaction waves resulting from addition of the two fundamental waves.  It's a very simple version of the summation of multiple instruments into the orchestral waveform - and the IM products among all the instruments are in there too.

[fas42]

1 minute ago, bluesman said:

I never said they would.  The natural intermodulation of two tones does not happen at the speakers.  The IM tones are generated by the interaction of the two waves in the air.  They're real, audible airborne compression-rarefaction waves resulting from addition of the two fundamental waves.  It's a very simple version of the summation of multiple instruments into the orchestral waveform - and the IM products among all the instruments are in there too.

 

Therefore, that test procedure I linked to is invalid - if intermodulation occurred in the air, the microphone would register it - and we still wouldn't know how well the microphone performed, as regards internally generated IMD ... does this make sense?

[bluesman]

9 minutes ago, fas42 said:

 

Yes, it's there, but it was created by the instrument itself - some part of it resonated at that frequency, provoked by the plucking of the strings - it's part of its intrinsic nature, its character - not added by the vibrations in the air interacting.

There is simply no way that a 26 Hz tone was generated by any part of the guitar (which is a solid body of neck-through construction with no resonances within 2 octaves of 30 Hz).  And I get the same spectrum from the same maneuver on 4 other guitars, including a big body hollow flattop, a 17" archtop, a National tricone, and a 3/4 size Kubicki Express.  I just don't see how your explanation could possibly be correct.

[bluesman]

17 minutes ago, fas42 said:

 

Therefore, that test procedure I linked to is invalid - if intermodulation occurred in the air, the microphone would register it - and we still wouldn't know how well the microphone performed, as regards internally generated IMD ... does this make sense?

Sure - but distortion in microphones is pretty far afield from acoustic intermodulation among instruments.  I’m not even sure how it got into the discussion.  Then again, it’s a great example of a misleading measurement in the context of acoustic intermodulation. 🙂

[sandyk]

46 minutes ago, pkane2001 said:

Now, compare that to IMD levels in an audiophile amplifier, say an SET.

An Audiophile amplifier is supposed to be more like a straight wire with gain.. 😉

[fas42]

22 minutes ago, bluesman said:

Sure - but distortion in microphones is pretty far afield from acoustic intermodulation among instruments.  I’m not even sure how it got into the discussion.  Then again, it’s a great example of a misleading measurement in the context of acoustic intermodulation. 🙂

 

It got into the discussion, because we're talking about how IMD would be registered by a mic. First of all, the mic itself must not misbehave, to any significant degree, because then if we got a reading we wouldn't know whether it was a true picture of what was happening, or the mic intermodulating, in its workings. So we need to test for this. Which is what that above test is about. Now, you said,

 

Quote

The natural intermodulation of two tones does not happen at the speakers.  The IM tones are generated by the interaction of the two waves in the air.  They're real, audible airborne compression-rarefaction waves resulting from addition of the two fundamental waves

 

Which means that even if the microphone was in fact perfect, that it would register IM, from those two speakers. So, running this test is useless for the purpose of detecting whether the microphone is misbehaving, adding IM from internal poor quality - by your thinking. Therefore, why do microphone manufacturers use this for a test?

 

[Clockmeister]

Good Grief

Are you chaps still discussing the finer nuances of which measurement is quintessentially required for choosing a dac and which analogue signal generator is preferable for viewing said IMD? and does a dac produce big staging or deeper soundscape? 😂

 

For all intense and purposes it looks like a early 1980's freshman debating society (entry level pyrotechnical collage) attempting to ascertain whether a large celestial body moving at near right angles to a star system causes a cup of tea to brew slightly better than using the uncertainty principle 🤔

 

I remember not so long ago PM of infamous Hifi news once stated during a particular audio show he could accurate predict the sound of any digital to analogue converter by purely viewing the side-band FFT spectral plot regardless of which system it was attached to 🤣

 

With regard to certain makes of dac exaggerating the reproduced sound, indeed some do, though that is how the designer wished the finial product to deliver the sound. This will appeal to a group of people that appreciate an 18 foot Eric Clapton (🤐) preforming for them through the big Wilsons, Magico's, Logan's or JBL's great if that is what you desire, job done.

 

Other prefer a more realistic approach to sound reproduction and will purchase another device of their choosing which they find more suitable for own tastes.

 

One contributor made a valid point of concerning mastering of recording and how they manipulate effects sounds in relation to sound staging  and perceived depth in the recorded material.

 

Some dac's have better channel separation and IMD than others, some have dual independent power supplies not just for analogue and digital sections but dual mono channel supplies. Some use tube followers, other op amps, though a fully discrete current to voltage section correctly designed and instigated does takes some beating. Though most dac designs do tend to have issues with correct digital and analogue grounding in relation to both the dac chips, receivers, SRC's and other associated supporting circuit structure.

 

All of these features can and do affect the way the finished products, very easy to produce a dac with wide open staging and cavernous depth, though does it actually have the correct tonal balance, textural rendering and articulation................?

 

As I have mentioned before measurements are your guide, how you interpret and use them to achieve the end result is down the the experience of the individual design team.

 

The are many ideas and creativity used in coming up with dac designs, some firmly believe in the NOS approach feeling its the one true close to analogue way. Some find that a plethora of PFGA's are the way to go, 1 million taps LOL is a Chord Dave truly capable of producing music or just an impressive two dimensional sound that can be grating? (answers on a post card). Just think 4 amps running a round inside a dac casework with all that RFI lovely 🙃. Ladder dac's?, piling up as many dac chip chips in dual differential configuration to achieve ultra low THD and S/N ratio's (or stuffing 8 dac chips on one substrate) or just looking at the whole aspect of a digital to analogue converter and making sure you are addressing the issues that really matter to produce a sound that will be desirable to potential purchases at a price that is appealing.

 

Providing you have decent implementation of digital and analogue grounding in the design, paid careful attention to RF ingress and circuit board layout and connection screening and selecting a suitable interface between dac and transport.

Then the majority of the finalized sound will come from the power supplies, routing on the board, decoupling isolation plus a quality I/V stage. Some of the most desirable dac's are not ruler flat 20hz-20Khz  with immeasurable IMD or S/N in excess 138dB or with distortion figures of less than  0.0001%. The fact that human hearing is limited to around 130dB never mind the frequency roll off as we progress through life is chasing the sonic dragon a life or death situation 😵

 

Remember your system is only as good as the weakest link no matter how good the rest of the system, does you amplifier have a S/N of least 128dB and is not anodyne or dry? Can your speakers actual resolve all of the information that dac has the potential to deliver? Never mind the  quality of the actual software music files or streaming services.  We have not touched on transmissions lines, amplifier speaker impedance's or let alone the most import aspect of all to quality sound room / speaker interactions.

 

Audio is a funny old game it really brings out the best and worst in people much like opposing football team (soccer) supporters in a local derby.

 

 

 

 

 

 

[Audiophile Neuroscience]

4 hours ago, fas42 said:

 

It got into the discussion, because we're talking about how IMD would be registered by a mic.

 

Yes but unless I've just entered the twilight Zone (distinctly possible) @bluesman is not talking about what you keep arguing about.

 

4 hours ago, fas42 said:

 Therefore, why do microphone manufacturers use this for a test?

 

for testing microphones?

 

I and David (bluesman), he more expertly than I, are playing with the idea that Tartini tones are not [exclusively] creations of the cochlea but as reported elsewhere, actual physical sound wave interactions occurring in air.

 

The question is can superposition of sound waves do this. There can be nodes and anti-nodes and beats but I am not sure about continuous separate modulated tones

[Clockmeister]

On 7/10/2020 at 7:20 PM, tapatrick said:

As a possible member of an 'amorphous' group and as someone only mildly interested in measurements, if this statement is true (i.e. putting me off a BM DAC) can anyone explain why I should be more interested in measurements? Honest question.

tapatrick

 

As someone who spends his life with measurements of some form or another for various EE work they are important to greater or less degree according to the project involved or the end product being designed.

With regard to audio, the accepted holy grail is a ruler flat 20Hz-20Khz frequency plot, ultra low distortion/IMD and high signal to noise ratio. All of the traits are desirable yes, do they tell you the whole story no, are the helpful yes without question.

 

I own all three BM dac's  which one do I prefer the MK2 for myself it produces a more pleasing sound that i can listen to for longer periods. Where as the MK3  has improved detail, slightly better separation and deeper bass. In that respect the later device is superior. In terms of enjoyment and wanting to listen to it personally the MK2 is the preferable model.

 

The system they have been used in can display more than sufficient resolution to delve into the very top digital products from DCS/Esoteric/MSN/MBL/TAD/Bricasti etc.

 

From your own point of view and others my suggestion would be do not dismiss any products until you have auditioned them in your own listening environment and lived with it for a good week or so, then only you can make the decision on whether you wish to purchase said device. My other suggestion would be take your time, do audition a few other devices never make knee jerk reactions and always consider yourself the prime mover in the decision to buy, not five chaps  from a forum who swear its great, only you can  do this within your own time and your own listening space, have faith in your own convictions. But most of all enjoy your music

[fas42]

3 hours ago, Clockmeister said:

All of these features can and do affect the way the finished products, very easy to produce a dac with wide open staging and cavernous depth, though does it actually have the correct tonal balance, textural rendering and articulation................?

 

 

So, it's possible to build a DAC which for a recording where the performer is in a tiny sound booth, will make it sound as if he is in a cathedral ... I'm curious if you can point to some guidelines of how one can do this ... ?

[fas42]

3 hours ago, Audiophile Neuroscience said:

 

I and David (bluesman), he more expertly than I, are playing with the idea that Tartini tones are not [exclusively] creations of the cochlea but as reported elsewhere, actual physical sound wave interactions occurring in air.

 

 

I think other people are in a Twilight Zone ... where IMD can occur in the air, and people can hear this; but mechanical devices like microphones can't ...

[pkane2001]

3 hours ago, Audiophile Neuroscience said:

The question is can superposition of sound waves do this. There can be nodes and anti-nodes and beats but I am not sure about continuous separate modulated tones

 

This is not the first time it's been mentioned here. Beating and the "superposition" of sound waves is not intermodulation. Intermodulation has a very specific definition in audio and signal theory, and addition of sine waves causing troughs and peaks or even completely canceling each other is not it. I suspect that a lot of this discussion is going in orthogonal directions simply because the wrong terms are being used.

[Audiophile Neuroscience]

51 minutes ago, fas42 said:

So, it's possible to build a DAC which for a recording where the performer is in a tiny sound booth, will make it sound as if he is in a cathedral ... I'm curious if you can point to some guidelines of how one can do this ... ?

 

Oh, making a performer in a tiny sound booth sound as if he is in a cathedral is child's play. There is is a guy here on this very forum who just by allowing his brain to focus can make any bad recording sound like a masterpiece. Not only that but he can do it by tinkering with the cheapest of gear ! Its unbelievable ! 🙄

[Clockmeister]

59 minutes ago, fas42 said:

 

So, it's possible to build a DAC which for a recording where the performer is in a tiny sound booth, will make it sound as if he is in a cathedral ... I'm curious if you can point to some guidelines of how one can do this ... ?

 

Fas42

 

Pretty basic requirements there, if this is want you wish for then DSP is your friend I believe its been on the market for one form or another for many years in many products, whether it accurately does this is another matter 🤔

[John Dyson]

The confusion between 'intermodulation' and simple addition of waveforms starts happening because there are so many sources of IMD, that it seems to happen in so many places.  For example,  I seem to remember that  human hearing does make a kind of IMD based upon multiple signals, but that doesn't mean that much IMD exists in the air (unless levels become extreme), or the transducer/vibrating device has movement.

 

In reality, when two sine waves are added in air -- say, 100Hz and 1kHz, there isn't a 1.1kHz/900Hz product produced in the air, unless pushed to extreme signal levels.   If the vibrating media producing 1kHz is influenced by the 100Hz signal, it is very likely to produce distortion from doppler effect, or nonlinear effects in the vibrating device itself (and probably other effects that I don't know much about.)

When not pushed to extremes, air itself is linear, but there are strange real-world effects that create mixing products.

 

I could be wrong, but I do remember that there are cases where hearing will produce false/misleading distortion products in certain cases, or the various characteristics of vibrating strings, etc -- they can mutually affect each other.  This is akin to a single speaker cone, it can easily produce IMD (doppler distortion specifically.)   Doppler can happen even without nonlinearity, but simply because of movement (the doppler effect.)

 

John

[Clockmeister]

On 7/8/2020 at 10:04 PM, pkane2001 said:

 

Why? When Amir started measuring Schiit equipment, their performance was mediocre at best (that's the measurable performance). After getting criticized and after seeing poor results from a third party, Schiit implemented a test regime to QA all their equipment using an AP analyzer. They also started publishing detailed measurement reports for each product. Not only did these published measurements improve their image, but the performance of their equipment rose by an order of magnitude, from mediocre to top of the line. Instead of spending time and effort to defend the poor quality of their older products, their products now get a recommendation from Amir because they perform well. And the consumer gets a confirmation that the manufacturer isn't exaggerating by seeing independent measurements. A little third-party verification can work to the benefit of the consumer. Not a bad thing, IMO.

Hello pkane2001

 

 

Apologies I did not see your reply.

 

I am sorry but this is just basic R & D that should have been performed before it got anywhere near asr (or public domain access media).  I appreciate they have rectified the situation now, however it should have never have got to that point in the proceedings in the first place, which projects sloppy business practices.

 

Yes the fact they have put things right and make sure acceptable QA in place is good move, but then it was business suicide to let your product loose with an agenda filled third party. Hence why preventative action was taken

 

Also demonstrating you have installed your own meas suite and are prepared to publish this date is noteworthy and more companies should do this agreed.

 

Caveat here is this though:- not difficult to fudge the readings by anyone with half the knowledge required to make the end result look good. I am not suggesting for one moment they have done this (or anyone else).

 

This is my rational for independent UNBIASED approved test house to conduct tests for say magazines both printed and online, that way any possible cronyism and suggestions of we will loan you a pair of DartZeel mono blocks, Tad CR-1's or Taiko master streamer on a long term loan would never enter into the equation.

 

Manufacturers using these tools to improve their products I would expect as a matter of course in the electronics area and it gives them confidence that their products do exactly what it says on the tin.

 

For example I am working on a new power supply and currently running through EMC pre compliance testing, am confident when this device is presented for official CE certification examination I will have only minor issue (s) to resolve and working with a flexible testing house also pay dividends when you wish to use equipment even we do not own!

 

CE testing is not an expense many firms at this level realize in their budgeting  strategy it can cost from £300 -£5K a day for testing and in some cases (testing houses) if you fail the clock starts again right back at the first test! ouch in the wallet.

 

So by performing all of the conceived testing possible, you can dramatically cut down on testing costs and through up bonus items especially with ac noise.

 

Having worked for a few US audio companies I can say CE testing they really have no concept of they see it as  'wasting my tax dollars' or ' Government conspiracy to leech your funds'

 

remember no CE no sales in the EU, the company can type approve no problems and the phrase 'all due diligence' is banded about quite a lot, have a two foot thick build manual, BOM's etc Though as my legal representative points out ' Type approve, onus is on the company to prove its safe' CE marked the state has to prove its unsafe.

 

Anyway I do understand your point thanks.