Oh I really do understand how it works Arny, btw most of the tests proposed into looking at IM forget musical content (putting keys to the side) is at least 40db-70db lower at ultrasonic levels, this is further compounded that IM will be at least 60-80db lower in sub 20khz region for a good product.
I don't think that how IM works is much of a mystery to those who are technically well-informed. But, for the average audiophile...
I find it hard to believe that so much equipment has been indicted by my little test for HF IM, but the facts are the facts. For instance, the PC I'm using right now passes the test. It uses an Asus Xonar DG audio interface (net price about $30), and the headphones are Superlux HD 668 the infamous Beyer DT 990 clones (net price $40).
The justification for the severity of the IM test that is included with the Keys Jangling file is that the Jangling Keys file itself is itself so severely composed of ultrasonics.
Here's a spectral analysis of the Keys Jangling file:
As you can see, it is highly atypical.
The background for this file is that I intended it to be a training file for some ABX sample rate tests involving more typical music, some 14 years ago. Things we
nt cattywumpus when a file this severe stumped my listening panel, and apparently the 100's or 1,000s of people who downloaded from my old www.pcabx.com web site. There were no, zilch, zip reports of reliable detection at the time and for 3-5 years thereafter until I took the site down. I have posted it infrequently since then, and no change.
Another aspect compounding this is to hear the sub 20khz IM one has to really turn the volume up, so hence you are now seriously stress testing an amp that has near full ultrasonic energy while the IM spectra amplitude is much lower than even normal music (again lets take keys out of this for now).
Modern amps should have no problem with these files. I'm worried about people going wild with their volume controls and taking out some tweeters. There are reports of AVRs going into protect mode due to enthusiastic playing of these files.
Everyone I have read on various forums using that test had to turn up the volume really loud; meaning they are seriously stress testing/or clipping the amp/or pushing it into non-linear behaviour due to the high crest factor-energy difference between audible sub 20khz and the extreme ultrasonic tones (usually close to or at 0dbfs).
The purpose of the test tones is to identify substandard monitoring chains and the people who are abusing good ones. Amir has been lavish with heaping criticism on my current hearing abilities, but if I use a monitoring chain that fails with the test tones, even I can reliably hear a difference with the Keys Jangling file.
BTW which product headphone amp failed your measurements and are those measurements on the web; am seriously interested to know.
Palindromic brand name should be a big hint! ;-) You oppo(sic) be able to figure it out! I don't recall if it was a 103 or 105.
Furthermore did that headphone pass the 19+20khz standard when pushed to same limit as higher tones therefore extreme loud volumes?
Send me an Oppo 105 and I'll test it! ;-)
The tests you do seem (I appreciate IMO) to comply with Dr David Griesinger conclusions that to hear IMD caused by ultrasonics even from keys one has to push a good/well designed product into clipping/non-linear behaviour.
Yes, even the best equipment will fail my test tones and show spurious audible differences if pushed into clipping. This program material is highly atypical in the interest of obtaining a positive result at almost any cost.
As I showed earlier with the Asus integrated DAC-Headphone it has exceptional low IM measurements (albeit using organisation international standards test measurement for IM rather than ones proprosed on forums).
One of the surprises is that some equipment will fail with some test tone pairs, and not others. They way they fail is also inconsistent with failures being either the generation of a spurious but fairly pure 4 KHz tone, or generation of a nasty sounding rather impure 4 KHz tone, or something else such as random sounding noise or squiggly sounds, or all of the above. Furthermore, IM has been traced to both electronics and transducers.
Asus is a good example to use because they are one of the worlds largest PC component manufacturers out there including critically motherboards with integrated audio/lan/usb/etc.
I think that many know that my day job is as a developer, builder, installer and servicer of PC-based system ranging from laptops to high performance desktops, to LANs I've been using and recommending primarily Asus products for over 2 decades. This policy has hurt my business because of their reliability. I was just repairing a LA where all the Asus-powered desktops and server had been in daily service for over 12 years, and other than the minor failures I addressed (primarily with the LAN wiring after a new phone system was installed).
Just to add though, should be noted Amir and maybe a couple of others (appreciate again not conclusive from a mass test but one meaning some seem to be identifying differences that were not meant to exist so one has to look at more than just IM) also did the ABX with music, which one would have to accept would not have the unusual ultrasonic amplitude/energy such as jangling keys or near 0dbfs dual ultrasonic tones.
Right. But when many try and only one seems to succeed, you don't have a new global rule, you have cause for more investigation.
While we cannot say this for all, we do know Amir mentions he did playback closer to normal listening levels than extreme loud/stress test component level.
Edit:
Just to add, I am not categorically saying IM is not the cause, but it is very unlikely compared to other possibilities and especially if those doing the ABX are using well designed products and listening in a way to not push components into clipping or non-linear behaviour.
For the record, no test of the Keys Jangling file is valid unless the test tones at the end of the file have been also tested without changing any volume control settings. The correct files may be downloaded from this URL:
https://www.dropbox.com/s/ylrjezd7vc11leo/keys jangling with test tones.zip and only this URL. All other files and all other testing procedures are invalid.
