• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Topping D90SE Measurements (DAC)

OP
VintageFlanker

VintageFlanker

Major Contributor
Forum Donor
Joined
Sep 20, 2018
Messages
2,996
Likes
9,171
Location
Paris
Can you run same 44.1k multitone test with your Cosmos running at 384kHz and show the full 192k bandwidth of multitone result? I am seeing something with my Cosmos and wanted to see if it is anti aliasing filter related or something else.
There you go :
Capture d’écran (1007).png


PS: It is the Matrix, not the D90SE.
 

bennetng

Major Contributor
Joined
Nov 15, 2017
Messages
1,454
Likes
1,392
Not the first time. Likely MQA related.
 

theREALdotnet

Active Member
Joined
Mar 11, 2022
Messages
262
Likes
313
I wonder why we’re still seeing anti-aliasing (the slope starting around 20kHz going down towards the left until it sinks into the noise floor around 600Hz) with 384kHz sampling rate?
 

theREALdotnet

Active Member
Joined
Mar 11, 2022
Messages
262
Likes
313
IMD caused by ultrasonic artifacts can reflect into passband as well.

Ok, but starting at 192kHz, shouldn’t they be way, way down at 22kHz? The plot above looks very much what I’d expect from a 44.1kHz sampled signal. Isn’t the point of higher sampling rates that those artifacts are much further up high and therefore much easier to filter (i.e without having to resort to aggressive filters)?
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
2,844
Likes
1,551
Would be nice if @amirm 's multitone's for DACs could always show up to 100kHz, to see this kind of crap (crap = not part of test signal) that gets hidden when plots stop at 22kHz

Right around the corner from 22kHz... can be nice surprises like this.
 

bennetng

Major Contributor
Joined
Nov 15, 2017
Messages
1,454
Likes
1,392
Ok, but starting at 192kHz, shouldn’t they be way, way down at 22kHz? The plot above looks very much what I’d expect from a 44.1kHz sampled signal. Isn’t the point of higher sampling rates that those artifacts are much further up high and therefore much easier to filter (i.e without having to resort to aggressive filters)?
Pay attention to the Matrix plots from both VintageFlanker and manisandher. The MQA filter is much more relaxed than some of the "fast" ESS filters. For example the ESS linear phase fast filter has 120dB attenuation beyond 24.1kHz for 44.1kHz sample rate.

192kHz is the ADC measurement bandwidth, not the input sample rate to the DAC.
 

theREALdotnet

Active Member
Joined
Mar 11, 2022
Messages
262
Likes
313
192kHz is the ADC measurement bandwidth, not the input sample rate to the DAC.

Exactly! And exactly! The rate that the DAC is operating at would likely be much higher than 192kHz, probably at 384 or 768 (or whatever the equivalent to the SDM rate is the DAC is actually working at). Anti-aliasing artifacts at this amplitude should not occur during high-rate D/A conversion, they should have died down way up in the ultra-sonic. Perhaps @Miska can be bothered to weigh in, he seems to understand these things.
 

theREALdotnet

Active Member
Joined
Mar 11, 2022
Messages
262
Likes
313
Then again, zooming in on the Y axis it appears that the artifacts top out at -135dB or so. So perhaps this is what we should expect from a 384kHz test signal after all. I’m not going to lose sleep over something at -135dB ;)
 

bennetng

Major Contributor
Joined
Nov 15, 2017
Messages
1,454
Likes
1,392
Anti-aliasing artifacts
There is no such thing as "Anti-aliasing artifacts". We are talking about Cosmos ADC's anti aliasing filter. DAC artifacts beyond 22kHz for 44.1kHz sample rate are called imaging artifacts, not "Anti-aliasing artifacts".

If the DAC is infected by a botched MQA firmware, then the issue should be fixed first before looking into other upsampling methods.
 

bennetng

Major Contributor
Joined
Nov 15, 2017
Messages
1,454
Likes
1,392
The multitone result in post #81 is at least strange. PC re-sampling?
An MQA issue:
 

pkane

Major Contributor
Forum Donor
Joined
Aug 18, 2017
Messages
3,247
Likes
5,723
Location
North-East

theREALdotnet

Active Member
Joined
Mar 11, 2022
Messages
262
Likes
313
DAC artifacts beyond 22kHz for 44.1kHz sample rate are called imaging artifacts, not "Anti-aliasing artifacts".

Ah, I’m talking about the stuff below 20kHz, not above.
 

theREALdotnet

Active Member
Joined
Mar 11, 2022
Messages
262
Likes
313
Then they are IMD, not "Anti-aliasing artifacts".

Pardon my muddled terminology, if anything it would be aliasing, not anti-aliasing artifacts. But yes, from what I understand, aliasing is the result of intermodulation between the signal and the sampling frequency.
 

pma

Major Contributor
Forum Donor
Joined
Feb 23, 2019
Messages
3,005
Likes
6,036
Location
Prague
Yes, mirror images should not get below 0.5 Fs. Even worst case should not. (No aliasing in case of DAC). Nonlinear distortion, as mentioned by @bennetng

1649334668586.png
 
Top Bottom