Yes, dbr measurements require me manually setting the reference and it seems I did not do that for the first graph.Amir, can you please explain something about these two graphs? They should be portraying the same phenomenon, but it seems to me that the dB scale on the Khadas one is either wrong or it was measured differently, since the -40 dB and -30 dB tones are peaking at -10 dB and 0 dB respectively.
Oh, so the NAD M51 graph is incorrect? I thought it was the other way around.Yes, dbr measurements require me manually setting the reference and it seems I did not do that for the first graph.
ref: https://kenrockwell.com/audio/apogee/duet-2.htmLow-Level Linearity measurements top
A -60 dB to -120 dB glide of a dithered 500 Hz sinewave into noise sounds fine, with no distortion. With the Ultrasone Edition 8 plugged in the front, I could hear a clean 500 Hz tone out to 0:24, or -108 dBFS, in a 16-bit track (CBS CD-1 track 20).
Apogee tells me that the analog levels are all controlled in the analog circuitry, with the DACs always run at full level, however listening to this and other very low-level sine-wave tracks, increased distortion is quite audible when the headphone gain is set around the -30 to -40 dB range with very low-level test tones (especially on CBS CD-1 Track 19, dithered 1 kHz at -70 dB FS), suggesting that Apogee might be getting some of the gain range by truncating the digital signal to the DAC. I don't know; 63 dB attenuators aren't that difficult to implement, and I do know that I tested the frequency response also at -20 and -40 dB attenuation, and it was exactly as it was at 0 dB attenuation, which is critical for professional monitoring.
I don't know, but I do know that the Apogee Duet 2 sounds great with music, and with high-level and with low-level test tones at the levels you'd listen to them, and that test signals are for dweebs. The fact that I can break it with very low-level tones set to a narrow range of lower output levels simply serves me right: so what if the Duet 2 isn't very good at doing something no one buys it to do?
There is no distortion audible with normal test signals or music at attenuated settings; it sounds great!
It may. I may try to same listening test to see if I can hear the distortion.
We hope that in 2-3 weeks , we will do very extensive testings on Ess hump and getting rid of it . As per H , special attention was given to the clocks , decoupling of the opamps , feedback R (we will try multiple values) and noise on opamp rails (maximum 1uV).. I think key to solve it its a combinations of all of the above especially clocks (I still think that syncronous clock is a must and all DACs whitout the issues seem to be syncronous) and opamp rails. If you look at any DACs that do not show the hump , they have one thing in common . Very good engineering (along with higher price) . Most companies approach implementing Ess SOC with minimum requirements (to be low priced) and get good THD numbers at 1Khz while exhibiting the hump.
This hump , its clearly solvable. The challenge is to make a unit that its competitive with Topping , Khadas .
Thanks for the update. We are all waiting holding our breath that you succeed and tell us how.We hope that in 2-3 weeks , we will do very extensive testings on Ess hump and getting rid of it . As per H , special attention was given to the clocks , decoupling of the opamps , feedback R (we will try multiple values) and noise on opamp rails (maximum 1uV).. I think key to solve it its a combinations of all of the above especially clocks (I still think that syncronous clock is a must and all DACs whitout the issues seem to be syncronous) and opamp rails. If you look at any DACs that do not show the hump , they have one thing in common . Very good engineering (along with higher price) . Most companies approach implementing Ess SOC with minimum requirements (to be low priced) and get good THD numbers at 1Khz while exhibiting the hump.
This hump , its clearly solvable. The challenge is to make a unit that its competitive with Topping , Khadas .
Hardware change (major) is needed.Johan,
I guess that
Thanks Johan,
I guess that this will not be solved via Firmware upgrade... Can you please confirm this point?
Regards,
Manuel.
I think key to solve it its a combinations of all of the above especially clocks (I still think that syncronous clock is a must and all DACs whitout the issues seem to be syncronous) and opamp rails. If you look at any DACs that do not show the hump , they have one thing in common . Very good engineering
Amirm would you include this two files into measurements for ess devices in the future?Thanks for the update. We are all waiting holding our breath that you succeed and tell us how.
Would you try the 2 files I posted? Thanks.Hi there, I do not follow that thread but if anyone interested in the root cause of that "hump" phenomenon I have to show something. The attached plot is power sweep vs THD+N my tiny ES9038Q2M USB->DAC->HPA dongle on real planar headphones loaded Fs=44.1kHz 24b. 100MHz named curve correspond reg#0 value 2’b00: MCLK = XI (default), 25MHz at 2’b11: MCLK = XI / 8. As you can see the blue 100MHz curve has no hump at all, and you can ask me why some DACs uses lower MLCK value? Check this out(note: FFT after 40db notch), harmonics distortions
distribution is quite different for 100MHz vs 25MHz, however THD+N very close for both modes. 25MHz mode has nearly perfect harmonics set - 2, 3, 5.. and nothing more, then 100MHz has lot's of small nails at 15, 17 and 19khz. I made some buttonless "easter eggs" hidden interface for my #9038S USB->DAC->HPA dongle to let user switch between 3 modes:
1) Normal-mode 100MHz
2) Performance-mode 25MHz
3) SE-mode 100MHz+.25% of 2nd harmonicView attachment 25726View attachment 25729View attachment 25730