@Miska
Why not measure into the GHz range ?
In the many EMC tests I have done often there is a lot of life well above 5MHz.
I measure also higher, but there's usually nothing because the analog reconstruction filter cuts out. Typical analog filter is 2nd order with
fc=100kHz so it has rolled off dirty output by 5 MHz already.
Taking one of the dirties devices I have (in that respect), Focusrite Forte. Almost all the the junk is in first 10 MHz band.
Most amplifiers do start to roll-off above 100kHz though some do not. granted this is mostly 6dB or 12dB/octave as input filters are generally only 6dB/octave and the amp itself as well.
Same for DACs. I used 4th order (24 dB/octave) for my own design though.
Do you have any practical shots/analyses of certain (preferably often used/well known) amplifiers loaded with actual speakers/headphones that clearly show problematic behavior of amplifiers when fed signals in the audible range and say around 1MHz combined which seem to show that when the 1MHz signal (preferably not a multiple of the test tone) is included or not that the output of the amp differs within the audible range ?
Without starting to write my own story here now, here's one example from other people:
https://www.diyaudio.com/forums/class-d/321632-hypex-ncore-nc400-input-anti-alias-filter.html
Why not multi-tone? Images are correlated multi-tone because they reflect music spectra around multiples of sampling rate.
Preferably with the main frequency say -6dB and the higher frequency at -60dB or so.
Where does this -60 dB come from? It is not necessarily even that much down.
I mean one can measure well outside of any audible threshold. What one can measure does not need to be audible. Some claim vice versa as well but I am not one of those people.
And I'm not one of those people who make claims about what other people can hear...
If it can be measured - it matters. If it cannot be measured, it still matters, but measurement resolution needs to be improved...
Is this your experience ?
Can you clearly correlate this ?
What amplifier / transducers are you using to listen for this (so I can avoid that one) as you clearly state they MAY create it I assume you own one to test.
One of the things you can simulate...
You seem to suggest that the often reported 'synergy' between DAC's and amps (almost infinite possibilities here) could (maybe) be related to this.
And loudspeakers. Metal dome tweeters combined leaky DACs is good example. Those tweeters have strong (typically at least +20 dB) ultrasonic resonance. Makes me feel like dentist drilling my teeth, or a bit like sound of the ultrasonic teeth cleaner they use (you may know what I'm talking about if you have experienced it).
This should be very possible to capture with an RME after an amp when loaded with a real load.
RME is not very voltage tolerant for such, unlike my measurement gear.
I don't like to make positive assumptions about amp behavior, rather negative worst-case scenarios. So I aim for clean DAC output that represents proper reconstruction instead of "half-assed" one.
Do you correlate listening tests with measurements ?
Are those listening tests 'blind'.
It's one thing to measure HF content but another thing to perceive it.
Yes, my own listening tests. Not blind. When I have two algorithms at hand, I have no reason to prefer A over B. I have my favorite algorithms based on listening. Some other people prefer other ones, that's completely OK for me. I offer options to choose from.
What's your current age (may I ask) and what is the max. frequency you can hear and what is the max. bandwidth you need to correlate recorded and actual sound quality ?
No you may not.
I don't know why what I hear matters to anybody else except me in first place. I usually don't talk much about my listening experiences unless specifically asked. Sometimes if people ask what are my favorite settings, then I tell my current favorite.
Do you have plots/graphs/examples indicating this within the audible band (preferably using nulling) ?
What I was talking about when this shit storm started, was
@Blumlein 88 's test tracks and the oversampling filter in question there.
Original reference track, here you can clearly see the transient hitting Nyquist due to typical "modern" halfband decimation filter used:
This creates aliasing band at the top, inside the transient. So this is the new form of TIM I was referring to.
Then the one that has gone through D/A - A/D loop. Since the DAC seems to have used ESS' "Hybrid" digital filter, it has largely removed that aliasing band and thus cleaned up the crap from the reference track:
Difference in that about 2 kHz wide band is tens of dB's.
At other point in time, on other forum I was referring for example to original CD version of Pink Floyd DSOTM that looks like the lower plot here. While the latest "modern" remaster looks like the upper one.
As I said earlier, this is what I mean the DAC in question is fixing with the choice of digital filter. Some other ESS filter choices are halfband and thus leave that aliasing band intact in the output.
Now what I don't understand is why this particular thing has caused this kind of shit storm towards me. I was just sharing my point of view about this detail based on spending 20+ years designing digital filters.
My products are not involved in this case. They could be and you have choice of both types of digital filter there, just like with ES9038 if the DAC offers option to choose the filter (like for example Pro-Ject Pre Box S2 Digital does). One test these things on their own if they like.