[XenHeadFi]

So, tell me your list of tests that should be used to characterise a DAC & "prove" that it is "audibly transparent"

Even Floyd Toole's talk said that IMD is way more informative than THD as THD may add "pleasant distortion" while IMD is usually adds "unpleasant distortion."

 

[mmerrill99]

You don't consider IMD to be on the list of things to test for in a DAC?

Do you bother to read the link before assuming that IMD & multitone tests are one & the same thing & asking a question which is already answered in the link??

 

[mmerrill99]

So, tell me your list of tests that should be used to characterise a DAC

Even Floyd Toole's talk said that IMD is way more informative than THD as THD may add "pleasant distortion" while IMD is usually adds "unpleasant distortion."

As I said to RROD - read the link first & inform yourself about what is meant by multitone test

 

[RRod]

Do you bother to read the link before assuming that IMD & multitone tests are one & the same thing & asking a question which is already answered in the link??

 
It says right in there:

"And…in terms of standard measurements, this DAC blew everything we’ve ever measured away. I mean, vanishingly low noise floor, virtually undetectable power supply harmonics, insanely low THD, flat frequency response…

…until you looked at the IMD, which gave numbers a bit higher than you’d expect, given the THD results. And the numbers weren’t related to the 1K spike…they appeared down low, below 100Hz."

 
They ran the multitone test AFTER the got an aberrant IMD result. What would they have done had they not?

 

[watchnerd]

  You don't consider IMD to be on the list of things to test for in a DAC?

 
So when you get bottom of the thread:
 
1. He notes that it had high IMD.
 
2. His multitone test is basically another type of IMD test
 
This seems reasonable to me.
 
The next questions are:
 
3. How well does this correlate with audible differences?  To Stoddard's credit, he doesn't claim a strong correlation
 
4. How much do other SD ADCs exhibit this?  Is this characteristic of the breed or just the Perfect DAC test subject?
 
And yet if you look at the IMD for the Schiit Gungnir DS vs MB, you see:
 
Gungnir
 
IMD: <0.002%, CCIR
 
Gungnir Multibit
 
IMD: <0.004%, CCIR
 
Okay, so the SD DAC actually has lower IMD...
 
So Stoddard might have found something, or it might be a red herring.  To Schiit's credit, Stoddard isn't claiming strong proof.
 
Seems pretty inconclusive at this point.

 

[mmerrill99]

Do you bother to read the link before assuming that IMD

It says right in there:

"And…in terms of standard measurements, this DAC blew everything we’ve ever measured away. I mean, vanishingly low noise floor, virtually undetectable power supply harmonics, insanely low THD, flat frequency response…


…until you looked at the IMD, which gave numbers a bit higher than you’d expect, given the THD results. And the numbers weren’t related to the 1K spike…they appeared down low, below 100Hz."

This is all about experience & interpretation - the IMD result was slightly higher and not related to the harmonics looked at when running a two tone IMD test - not something that normally raises any alarm bells?

They ran the multitone test AFTER the got an aberrant IMD result. What would they have done had they not?

I'll give you another data point about multitone tests from Scott Wurcer - the famous designer at AD & they haven't used these tests on audio DAC boards - this is what he's talking about in his quote, his testing of DAC boards

The multitone really separates the sheep from the goats. I'm using 30 1/3 octave tones at about 12db crest factor. Artifacts show up on even the best boards.

 

[mmerrill99]

 
You don't consider IMD to be on the list of things to test for in a DAC?

So when you get bottom of the thread:

1. He notes that it had high IMD.

Let's try to be accurate "…until you looked at the IMD, which gave numbers a bit higher than you’d expect, given the THD results. And the numbers weren’t related to the 1K spike…they appeared down low, below 100Hz.

2. His multitone test is basically another type of IMD test

Look at my quote from Scott Wurcer

This seems reasonable to me.

The next questions are:

3. How well does this correlate with audible differences?  To Stoddard's credit, he doesn't claim a strong correlation

4. How much do other SD ADCs exhibit this?  Is this characteristic of the breed or just the Perfect DAC test subject?

And yet if you look at the IMD for the Schiit Gungnir DS vs MB, you see:

Gungnir

IMD: <0.002%, CCIR

Gungnir Multibit

IMD: <0.004%, CCIR

Okay, so the SD DAC actually has lower IMD...

So Stoddard might have found something, or it might be a red herring.  To Schiit's credit, Stoddard isn't claiming strong proof.

Seems pretty inconclusive at this point.

Again, let's try to be accurate - Stoddard said "What? We ran through our multitone test (it’s easy to do digital multitones on a Stanford as well, not sure about other analyzers) and the low-frequency numbers went bonkers. As in, there was a broad range of non-harmonically related distortion components from 10-90 Hz, at a fairly high level (-50dB or so). -50dB is potentially audible. And it was up nearly 90dB from the baseline measurement."

 

[charleski]

So you missed that he used a multitone test & found the problem in this "non-standard" measurement - do you still want the flawed pseudo-scientific DBT "proof" or did you want him to set up a large scale, rigorous & carefully administered blind test that has some semblance of scientific rigour?

For those interested Stoddards post is here

And the relevant section is at the bottom
So, tell me your list of tests that should be used to characterise a DAC & "prove" that it is "audibly transparent"

You've completey mis-represented Stoddard's post. They were given a DAC from another manufacturer, did some measurements, and found that, while most were quite acceptable, it suffered high IMD. He doesn't even mention any form of subjective listening test.

 

[RRod]

This is all about experience & interpretation - the IMD result was slightly higher and not related to the harmonics looked at when running a two tone IMD test - not something that normally raises any alarm bells?
I'll give you another data point about multitone tests from Scott Wurcer - the famous designer at AD & they haven't used these tests on audio DAC boards - this is what he's talking about in his quote, his testing of DAC boards

 
The IMD number was high enough to worry them: the standard test worked. It seems what you need to give us is a scenario where there is an actually (not potentially) audible IMD issue that the multitone test will pick up but that will past the standard IMD test without alarms.

 

[mmerrill99]

This is all about experience

The IMD number was high enough to worry them: the standard test worked. It seems what you need to give us is a scenario where there is an actually (not potentially) audible IMD issue that the multitone test will pick up but that will past the standard IMD test without alarms.

There's not enough detail in either of these reports to talk in absolute terms about what is a worrying IMD figure & what isn't but I'll put it to you that Scott Wurcer was using DAC evaluation boards in his multitone tests - do you really think DAC manufacturers release such boards (meant to showcase their DACs) with "worrying" IMD test results?

 

[charleski]

There's not enough detail in either of these reports to talk in absolute terms about what is a worrying IMD figure & what isn't but I'll put it to you that Scott Wurcer was using DAC evaluation boards in his multitone tests - do you really think DAC manufacturers release such boards (meant to showcase their DACs) with "worrying" IMD test results?

The IMD Stoddard measured was -50dB. That's 0.3%, shockingly bad for a DAC and almost certainly audible.
 
I'm bemused as to what point you think you're making here.

 

[mmerrill99]

So you missed that he used a multitone test

You've completey mis-represented Stoddard's post. They were given a DAC from another manufacturer, did some measurements, and found that, while most were quite acceptable, it suffered high IMD. He doesn't even mention any form of subjective listening test.

Yes, you are right, I should have gone back to the post instead of relying on my obviously bad memory - I mixed up this bit at the end of his post with what came before "That’s why we still listen. And measure. And come up with new measurements. And listen again."

But I still ask you what is your list of tests that you would use to "prove" that a DAc was transparent?

 

[mmerrill99]

There's not enough detail in either of these reports to talk in absolute terms about what is a worrying IMD figure

The IMD Stoddard measured was -50dB. That's 0.3%, shockingly bad for a DAC and almost certainly audible.

I'm bemused as to what point you think you're making here.

No that was not the IMD measured - that was the result of their multitone test
"What? We ran through our multitone test (it’s easy to do digital multitones on a Stanford as well, not sure about other analyzers) and the low-frequency numbers went bonkers. As in, there was a broad range of non-harmonically related distortion components from 10-90 Hz, at a fairly high level (-50dB or so). -50dB is potentially audible. And it was up nearly 90dB from the baseline measurement."

 

[mmerrill99]

This is all about experience

The IMD number was high enough to worry them: the standard test worked. It seems what you need to give us is a scenario where there is an actually (not potentially) audible IMD issue that the multitone test will pick up but that will past the standard IMD test without alarms.

Is anybody seriously going to try to maintain that a distortion which is non-harmonically related @ -50dB isn't going to be audible?

there was a broad range of non-harmonically related distortion components from 10-90 Hz, at a fairly high level (-50dB or so). -50dB is potentially audible. And it was up nearly 90dB from the baseline measurement.

 

[RRod]

Is anybody seriously going to try to maintain that a distortion which is non-harmonically related @ -50dB isn't going to be audible?

 
Of course it is, but in this case what caused it also caused the regular IMD test to bomb. I'm saying find me a phenomenon where it doesn't.