[Jason Stoddard]

Where are there specs for Asgard, Magni, Modi, Lyr, Valhalla? These are the old products I'm talking about.

This was mentioned in the past and I believe Jason said he would consider putting them back.

Aha, yep, no time to, unfortunately. It's on the list, but it's a LONG list.

 

[Tuco1965]

No problem. Just happy to hear it's still on the list.

 

[StanD]

 
Aha, yep, no time to, unfortunately. It's on the list, but it's a LONG list.

My wife has a list too. My requests get appended to the rear and stay there, it's a UTGD Queue, (Unlikely To Get Done).

 

[Currawong]

The multi-tone IMD test follows a thought I've had for a while. I've always wondered why an IMD test would only use two tones, rather than a spectrum of them, since music covers a spectrum. It'll be interesting to see what results down the track if this catches on as something manufacturers experiment with. 

 

[jcx]

like I suggested - most analog circuits aren't "smart enough" to recognize complex multitones and do something different
 
 
high number of frequencies in random multifrequency tests should be done - but really we have the experience in analog electronics to know not to expect much from them compared to the more focused, structured, higher intensity few tone stimulus testing
 
 
usually single and 2 tone tests are adequate to see most analog circuit's nonlinearity - IMD with swept and maybe wider frequency limits can be justified
 
the general principle for generating "hidden distortion" - distortion not found with a single tone - is that the analog circuit has 2 or more frequency dependencies that are combined in a nonlinear multiplier type distortion process
 
the common one is thermal modulation of gains - SMPTE aims at that - could be improved by using even lower low frequency tone, IMD testing in general does include sweeping the frequencies as a standard technique
 
RF has some specific structured 3 tone measurements, audio also has some "load soak" tests to look for thermal transient effects, may also catch weak power supply, poor psrr or protection circuits that distort well before going into protection mode
 
 
but with complex multitones as you go up in number of tones you have a crest factor problem - you have to keep the instantaneous sum below your circuit's max clipping level
 
that means the individual frequencies with random multitones have to be reduced in level roughly by the number of frequencies used - and their IMD products are functions of the individual input tone levels so your IMD per tone quickly goes down 
 
 
and that's before applying human hearing psychocacoustic principles of Masking and Critical Band Theory
 
Masking by adjacent frequencies is strong - 30 log spaced audio frequency test signals put signal in every human hearing critical band - and its hard to hear even 1% variation alongside another tone within the same hearing critical band

 

[jimvibe]

  unless you’re of the “current output” frame of mind, which I won’t discuss—but if it works for you, have fun!

 
Are you referring to current driven amplifiers? Is it just hard to lower the impedance in such designs or do they think it would sound better with higher impedance?

 

[artur9]

 
[size=small]... [/size]Of course, pure objectivists will say we’re fooling ourselves on that one. But hey, maybe if we can convince ourselves that there are differences when there aren’t, maybe they can convince themselves that there aren’t differences when there are. Neener. ...
...
So…while we putter around confidently with all of the accepted measurements, maybe there are still realms out there where “here be there monsters.”
 
That’s why we still listen. And measure. And come up with new measurements. And listen again.

 
Thanks again, Jason, for the insider's take.  The above is my favorite part, obviously, but begs a question.
 
Besides the human factors aspects, like the scratchy volume pot, what sort of things do you listen for?
 
I've read of a speaker manufacturer that keeps some musical instruments in the shop for comparison purposes.  Do you ever do anything like that?

 

[catspaw]

On the THD, correct me if Im wrong, but as far as I see it, its something that it rises exponential if you calculate the THD in all the audio chain.
 
What Im trying to say is, that while 1% THD total does not sound too bad in a headphone, if you have more in the audio track, the DAC the amp, and you add some noise into the mix, you can get some really nasty sounds.
 
Lets assume that a particular headphone is not great at the 4Khz mark.
If the THD of the audio track dac and amp does not touch that mark, the damage will be limited (in terms of audio quality) to the headphone THD.
 
However, what if the audio track has a strong 4Khz note that repeats from time to time, the DAC interprets it slightly wrong (sigma-delta), the amp makes it louder and distors it a bit more, and then it gets to he HP?
 
Well, thats a song you wont "like" on the HP as far as I am concerned.
 
Since no amp, dac and audio track has stable THD all across the 20hz-20Khz audio spectrum, its quite important to know as much about measurements as possible in my book.
 
Unless I am reading this wrong (correct me if that is the case).
 
So while I agree that in principle you wont hear THD much, its not the same to have THD where it wont hurt, and where its already hurting.

 

[johnjen]

One thing about these sorts of measurements I've come to understand is…
 
THD and its cousins tell you the amount of added energy at those frequencies, but not
And this is the kicker,
What the waveform shape at those specific frequencies is.
 
The analog signal shape at those frequencies is going to be different based upon which device is doing the contributing, ie. an amp is going to behave differently, vs. a DAC, or HP's etc.
This can all to easily have a compounding effect in that when the total of these interactive differences between these devices don't 'mesh well', it can sound rather 'unnatural'.
IOW their added harmonic contributions may not match well with those that happen when music is being played.
Think non-euphonic…
 
Which is why it seems to me that a test that uses the natural harmonic series of say strings, either being plucked, bowed, or struck would make a decent starting point for a multiple frequency test.
Of course other sound sources could also be used (reeds, percussion, horns, etc.) and lets not forget the richness of the human voice itself.
 
Of course coming up with a set of 'standards' for cross comparison would be a formidable task in and of itself.
 
Still, it seems to me, these sorts of tests using more natural harmonic series instead of those 'techincally derived' chosen frequencies, would provide a 'better' correlation to what we actually hear.
 
Just a thought or 2…
 
JJ

 

[judmarc]

Jason, thanks.  That was obviously a tremendous amount of work.  Couple of things particularly caught my interest:
 
- Noise way, way below what we can hear in any normal room (between -100db and -130db) could be a sign of instability in (rare?) real world situations.  I wonder if that might also imply real world situations in which the piece might, short of instability, become noisier or not sound so great.
 
- The multitone test: The piece of this that interests me is I've read several people comment about DACs with good reputations not sounding correct or natural to them, *especially in the bass*, and they (and I) wonder why that is when all the attention seems to be focused on the high end of the audible range and the near-ultrasonic (aliasing, ringing).
 
Edit: By the way, where did the idea for trying the multitone test come from?  Just "Hey, let's throw something a little more complex at it and see what happens," or something more sophisticated?

 

[jcx]

multitone testing is historical, "ancient" in electronics years - comes from Noise Power Ratio in radio - when you start fill the spectrum with close spaced frequency carriers then large power with high distortion in one channel, the harmonic and IMD products look like interfering noise in nearby frequency channels - so radio was the 1st place IMD and Harmonic distortion math was done
 
Black's invention of high negative feedback amplifiers was motivated by Bell wanting to use frequency multiplexing in long distance telephone lines which (eventually) required hundreds of amplifiers to  keep boosting the (wide band, multiplexed audio) signal across the width of America - early tube amps before his negative feedback invention had too much distortion to use even dozens in series for even a few frequency multiplexed voice channels
 
http://www.ieeecss.org/CSM/library/1993/aug1993/w04-HistoricalPerspectives.pdf
 
so Bell Labs was the next to work on distortion/IMD even if only for "voiceband" audio they still were the 1st for lots of important results, techniques - nearly all of the now recognized as "audiophile" passive components were pioneered by, then bought in massive quantity by Bell for their network for solid objective engineering reasons
 
with such long history multitone testing has been worked over in the math and extended in application - "System Identification" is another major application https://www.google.com/#q=system+identification so much so that you can view audio measurement theory today as a subset of System Identification Theory

 

[wink]

Quote:Jason Stoddard

 Maximum Power. This is how much power an amplifier can put out, usually expressed in watts RMS into a specified load, or multiple specified loads. For example, “15W into 32 ohms,” or “60W into 8 ohms and 100W into 4 ohms.”

FTFY.

 

[NA Blur]

"Because measurements are absolutely meaningful—it’s just that what measurements are meaningful changes at which part of the product development and production process you’re in. Without measurements, it would essentially be impossible to develop our products…and without deep, high-quality measurement capability, the products wouldn’t be as good as they are."
 
-- Jason Stoddard
 
 

 
 
I would add that measurements go beyond subjectivity and add to the quantifiable quality of a piece of gear.  Measuring something gives rise to repeatability in manufacturing as well as how each build and their myriad components work together.  Try designing an amp or headphone without taking any measurements or using any design tools.
 
It seems the big push against measurements these days is because they are hard to understand and when we think we have it down something comes along saying that the measurements we use to make comparisons, such as the sensitivity for headphones, is not really what we thought it was to begin with.  I would love to see more engineers and scientists alike come to this forum and show the public what to look for, how to interpret the specs, and how they may be used in determining sound quality.
 
The entire industry relies on subjectivity so the uneducated makes purchases based on gut and instinct rather than true measurements / comparison.  If we buy something that is supposed to be an improvement over something we already use, then it would make sense to either subjectively compare it side by side or take some measurements which is at a fundamental level what subjectivity is.

 

[jacal01]

Interesting insight for me to learn that transducers govern the audible impact of frequency response and harmonic and aharmonic distortions.  Makes me second guess myself for sneering at newbies who post about which TOTL headphones they should purchase for their dinky DAPs, iphones or entry level desktop rigs.  I think I've posted more than once to first upgrade their upstream components before trying to address any SQ deficiencies, detected or otherwise, at the 'tailpipe' component in the chain.

 

[mithrandir38]

Interesting insight for me to learn that transducers govern the audible impact of frequency response and harmonic and aharmonic distortions.  Makes me second guess myself for sneering at newbies who post about which TOTL headphones they should purchase for their dinky DAPs, iphones or entry level desktop rigs.  I think I've posted more than once to first upgrade their upstream components before trying to address any SQ deficiencies, detected or otherwise, at the 'tailpipe' component in the chain.

that's very humble of you to admit that. Most head fi /hifi junkie would double down and argue the point