Really bad resampling of 44.1kHz/16bits files with Fixed Resoultion SPDIF setting

[erazortt]

Dear all,

I have tested the output quality of the resampling which is being performed when Fixed Resoultion is selected for SPDIF Output Resolution. The Wiim Ultra is connected to a DAC via Optical and I measured the RCA output of the DAC. I tested the maximum setting of 192kHz/24bits with four files of the CCIF 19kHz & 20kHz dual tone, where these files differed only by sampling rate (44,1 vs 48 kHz) and bitdepth (16 vs 24). I played the files using the Wiim App.
The files with 44.1kHz/24bit, 48kHz/16bit and 48kHz/24bit are resampled correctly, however the file with 44.1kHz/16bit is not!
See the measurements below. (I am using the newest Firmware: 5.2.704665)

Greetings!


44.1kHz/16bits file: not ok


44.1kHz/24bits file: ok


48kHz/16bits file: ok


48kHz/24bits file: ok

 

[EddNog]

Impressive first post!!!

-Ed

 

[Burnside]

Dare I ask, can you hear the difference?

 

[canard]

It's annoying because it corresponds to the most common case "cd resolution"... such distortions on just one ccif...

 

[canard]

resampling should be avoided for the moment if this is confirmed...
A long time ago onlyoneme had already observed the strange impact of resampling...
if confirmed....it's up to wiim to investigate

 

[merifon]

Maybe there are dithering problems, passing from 16 to 24 bit and for not exact multiple sample rate.
Could you test even more combinations?

 

[Burnside]

Have you submitted your findings to WiiM via the more/feedback section in the app so they can inspect your logs and comment on your findings? Again, is this “bad resampling” audible?

 

[onlyoneme]

What happens if you reduce test signal RMS level slightly, let's say by 3 dB?

 

[erazortt]

Dare I ask, can you hear the difference?

Have you submitted your findings to WiiM via the more/feedback section in the app so they can inspect your logs and comment on your findings? Again, is this “bad resampling” audible?

Yes, this can be very clearly heared! The original file has tones only at 19kHz and 20kHz which due to my age I cannot hear, however what I hear in the case of 44.1kHz/16bit are all the other tones below 16kHz which are produced by the lacking resampling. Especally that group of four tones at around 10kHz are really obvious (look at the first spectrum in my first post).
Of course this is a constructed test case because I wanted to make the issue as clear as possible, however, this test is really a standard test for all music equipment. And think of what happens if you have not only two tones in the input, but a recording of a whole orchestra...

What happens if you reduce test signal RMS level slightly, let's say by 3 dB?

When the singnal is reduced, so are the artefacts, by the same amount.

Maybe there are dithering problems, passing from 16 to 24 bit and for not exact multiple sample rate.
Could you test even more combinations?

I can do more tests tomorrow, now it's already way too late to put my test setup back into place.

 

[erazortt]

Also, I want to make clear that the low frequency peaks at 60Hz, 120Hz, 180Hz, and 240Hz are not due to the Wiim but only due to my crappy equipment. I have just used a soundcard to record this. Nevertheless, the crapy soundcard does not invalidate my findings, since I also show the results where the resampling works as expected.