Actually this plot shows otherwise. That there is Frequency distortion as low as 5khz to 15khz. Granted there is very little granularity.Because distortion above 10K issupersonicultrasonic . What the multitone test shows is (at least at 5W) that higher frequency distortion is largely above 20KHz, even including IMD products folding back into the audible spectrum.
This brings partial light as to why but then it begs to ask why do Class-D amps get special testing?As I understand it, with a 40 khz filter as used by Amirm when measuring class D, everything IMD above about 13.khz are filtered out.
Asking this can only create an inflammatory disposition with the community. Not my objective.
This however leads to further scrutiny of Class-D designs with their known Phase Linearity issues and more specifically this Frequency Distortion above 5k. Generally it likely comes from the LC output filter(coil/choke capacitor) integral at the core of its design.. Since it shows it has frequency reactivity then it likely also has phase issues. I believe currently Harman Citation and Purifi are trying to address this in Class-D foremost at the moment.
Tons of AES papers on the properties of phase linearity in audio. Many companies extolled its value from the 70's on wards. Harman Citation designs called for High Bandwidth to 300khz or higher to address this so that the 1khz to 20khz were not phase shifted. Mark Levinson employs this discipline in design as well. Phase linear(the company) which became Carver I believe were clearly inspired. Benchmark isn't the only company that acknowledges it's importance in Amp Design Discipline.Your reference is a person who just happens to sell equipment marketed as having low phase distortion. At no point did you or him reference a study backing the claims on the audabilty of phase distortion at high frequencies.
Here's an example of a poor performing class a/b at Sinad 65db https://www.audiosciencereview.com/...on-2004-mk-ii-review-vintage-amplifier.29248/
This matches its frequency distortion plot and actually shows mostly linear frequency distortion. Even in poor performing designs Frequency distortion is mostly Linear.
NOTE:The Topping PA5 almost matches this level of frequency distortion plot at 10khz and 15khz and it clear that as frequency increases above 5k so does distortion in a frequency specific way.
Arguably the IMD is superior on the PA5 but we are told it these are special "Class D" filtered plots. More important is that Phase Linearity isn't tested/plotted and we can only extrapolate from the Frequency Distortion that it may lack linearity.
We all want to believe Topping made audio Nirvana for $350 but Topping did not design the TI TPA32XX chip with its potential SNR 111db THD they just implemented it well with its known inherent Phase frequency flaws and frequency distortion. Check TI TPA32xx Data Sheets.
I cannot dismiss what I see with my eyes nor hear with my ears.
What is most disconcerting is that many new people to audio will buy a PA5 as the new Budget "benchmark" reference thanks to ASR SINAD and become biased that this is the way Audio "transparency" should sound. Yet if the PA5 was implemented in a Multichannel ATMOS configuration with its potential phase linearity flaws it would become apparent. Especially if mixing amps.
I know this a long thread but a lot of your previous posts regarding sonic impressions and a few others correlate to exactly the issues I am addressing.Thanks J-Sine for this well written post. That Benchmark AHB2 would be nice, one day it will be mine. This PA5 has a lot going for it, most of the time it sounds really great. Sometimes, something sounds off to me but I am also comparing it to more expensive amps, Class AB designs...
For a stereo setup the PA5s flaws will likely bring a new clarity to certain instruments. Yet knowing that the sound stage is altered as an artifact the naturalness of many tones will be skewed. Other Class A/B designs with lower ranking SINAD with phase linearity will sound more natural but likely more generic. Knowing ones gear and its limitations allows you to use it more effectively. Much like home theater systems vs a 2 channel playback setups.
The PA5 exposes the "One SINAD to Rule them all" as potentially flawed and Class-D amps need further phase tests included.
Despite my aging ears I still listen above 1KHZ and the harmonics to at least 15khz and relative phase coherency matters. Speakers are still the greatest offenders and constant directivity design is trying to address them.
As a whole phase linearity does matter but to what degree is currently a hot debated topic. Class-D has brought it to the forefront again.