Issue with Distortion at Very Low Volume When Using WiiM Ultra with External DAC

[bherren]

It would give you a chance to understand the meaning of the citation.


It tells that if an incoming signal is marked as 24 bits, but the stream is in fact in 16 bits, then 16 bits are shown as coming from an analysis of the stream.

"Analysis of the stream" is not a very precise definition ... What does it actually do ? Look for all samples containing zero in the 8 low bits ? Again so what ? All that your interpretation says is the DAC may decide the stream contains fewer useful bits than what's advertised.

How can that possibly lead you to believe that somewhat the WiiM is sending more than 16 useful bits of data even when it pretends to only send 16 and that the DAC will somewhat retrieve those bits and use them even while only displaying 16b are being received ?

You just don't make any sense here.

Fact is that it does not happen.

I still have to see any actual evidence of this rather outlandish claim since it would imply that both the WiiM and all the DACs out there are violating the protocol standard.

I instead what we so have a logical explanation as to why attenuation of 16b into 16b will by necessity lose resolution along with some users observing this via audible distortion at very low volume which correlates.

 

[bherren]

The Wiim does not output 24bits for 16bits inputs, as long as it is not forced to do so via the "Fixed Resolution" setting. The reason why there is this beleif is that somewhere in the documentation, it is mentioned that the CALCULATION is done in 32 bits. This might be the case, however, this caluclated result is then rescaled back into the same bitdepth as that of the input as long as the "Fixed Resolution" setting is not enabled.

Thanks @erazortt , this is good data

 

[onlyoneme]

"Analysis of the stream" is not a very precise definition ... What does it actually do ? Look for all samples containing zero in the 8 low bits ? Again so what ? All that your interpretation says is the DAC may decide the stream contains fewer useful bits than what's advertised.

You can ask RME for details if you need it. Anyway, RME DAC ignores the metadata in the spdif stream and relies on the sample data instead.

How can that possibly lead you to believe that somewhat the WiiM is sending more than 16 useful bits of data even when it pretends to only send 16 and that the DAC will somewhat retrieve those bits and use them even while only displaying 16b are being received ?

I've no idea what are you talking about. DAC will use all the data in the sample.

I still have to see any actual evidence of this rather outlandish claim since it would imply that both the WiiM and all the DACs out there are violating the protocol standard.

I analyzed the metadata of the spdif stream sent by the WiiM in the past and I know what I've seen. By the way, there was the time when even the sample rate was not sent and it has been added when I asked for it.
It's up to you if you believe or not.

 

[onlyoneme]

The entire point of the conversation was about the effect of volume control, mate. Of course converting 16b to 24b isn't going in itself to change anything to the signal, nobody ever argued that.

The argument here is that large attenuation will cause a significant loss on 16b content if it's also transmitted as 16b content over spdif. It can be avoided using fixed resolution to force a bump to 24 provided WiiM does the bump before the attenuation which you seem to indicate they do, good. Though using fixed resolution unfortunately brings resampling into the picture too which in that case isn't desired

I see your point but my point was to show that there won't be any conversion from 16 to 24 bits if there is no audio data alteration. That's all.

 

[onlyoneme]

to support DAC level attenuation when on USB

Bad idea, no headroom again. Using a volume attenuator before the DSP chain in the WiiM is also needed for PEQ to avoid clipping.

 

[onlyoneme]

to support upscale to 24b without resampling as an option

Good idea indeed. I would say, to use 24 bit depth in case of any data alteration defined.

 

[erazortt]

to support upscale to 24b without resampling as an option

Good idea indeed. I would say, to use 24 bit depth in case of any data alteration defined.

There is actually no need for a user-visible option, this could be done automatically.
I have just opened a bugreport, suggesting to automatically increase the bitdepth for 16 bit streams whenever "Fixed Volume Output" is disabled and the 24 bits support is enabled by the user in the "Output Resolution" setting of the digital output. This would then be done without resampling as long as the "Fixed Resolution" is disabled.

 

[onlyoneme]

It might be needed even if the fixed volume is enabled but volume limit is used.

 

[bherren]

Bad idea, no headroom again. Using a volume attenuator before the DSP chain in the WiiM is also needed for PEQ to avoid clipping.

Do we know for a fact that attenuation happens before EQ in the WiiM stack ?

 

[bherren]

You can ask RME for details if you need it. Anyway, RME DAC ignores the metadata in the spdif stream and relies on the sample data instead.


I've no idea what are you talking about. DAC will use all the data in the sample.


I analyzed the metadata of the spdif stream sent by the WiiM in the past and I know what I've seen. By the way, there was the time when even the sample rate was not sent and it has been added when I asked for it.
It's up to you if you believe or not.

We are going to have to agree to disagree here and leave it at that

 

[bherren]

There is actually no need for a user-visible option, this could be done automatically.
I have just opened a bugreport, suggesting to automatically increase the bitdepth for 16 bit streams whenever "Fixed Volume Output" is disabled and the 24 bits support is enabled by the user in the "Output Resolution" setting of the digital output. This would then be done without resampling as long as the "Fixed Resolution" is disabled.

While I agree in principle, I think marketing won't because of the "bit perfect" monnicker

 

[bherren]

Bad idea, no headroom again. Using a volume attenuator before the DSP chain in the WiiM is also needed for PEQ to avoid clipping.

But that would be the only way to avoid the distortion at low volume for 16b content unless of course they switch to the suggestion of alway going to 24b in that case.

 

[onlyoneme]

Do we know for a fact that attenuation happens before EQ in the WiiM stack ?

Of course. Well... I know that, you don't.

 

[onlyoneme]

But that would be the only way to avoid the distortion at low volume for 16b content unless of course they switch to the suggestion of alway going to 24b in that case.

You said yourself that it is not the only way.

 

[onlyoneme]

While I agree in principle, I think marketing won't because of the "bit perfect" monnicker

It may activate in scenarios when bit perfectness is not maintained anyway.

 

[Musician]

Onlyoneme, can you do some measurements with 16 bit source material ( with output resolution to 24 bit in the Wiim menu ) , no fixed sampling frequency output , volume control used and spdif out ?

Digital volume control using spdif at 100, 80, 60, 40, 20, 10 and 1 ?

 

[Musician]

For anyone connecting to an external DAC, but not willing to use the volume control of that DAC, and instead using the volume control on the Wiim Ultra:
Use the SPDIF outputs (either Optical or Coax) and then enable Fixed Resolution at 24 bits and with any sampling rate your DAC supports apart from 192khz. This will enable the Wiim to always use 24 bits for its output, and thus enabling a high quality volume control.
This is not possible for the USB connection, so this follows the same logic as when Fixed Resolution is not enabled for the SPDIF outputs, meaning that the output bitdepth depends on the input bitdepth (If your input is 16 bits, so is your output to your DAC. Playing back mp3 is also done in 16 bits, while ogg and aac in 24 bits. Lossless formats like flac are obviously done in whatever bitdepth the file was created from.)

This is now possible as the resampling inside the Wiim Ultra was fixed with the firmware v5.2.705437.

Problem is that the Ultra sounds worse using fixed resolution 24 bit 96 kHz with 16 bit material, using spdif out during normal use to a dac, i.e having the volume control above 20.

Or have they fixed that in the new firmware ?

 

[erazortt]

While I agree in principle, I think marketing won't because of the "bit perfect" monnicker

It may activate in scenarios when bit perfectness is not maintained anyway.

As long as "Fixed Output Volume" is disabled, we can assume that the user wants to decrease the volume in the Wiim, so on the digital outputs the signal is anyhow not bitperfect anymore.

 

[onlyoneme]

Onlyoneme, can you do some measurements with 16 bit source material ( with output resolution to 24 bit in the Wiim menu ) , no fixed sampling frequency output , volume control used and spdif out ?

Digital volume control using spdif at 100, 80, 60, 40, 20, 10 and 1 ?

What for?

 

[slartibartfast]

Onlyoneme, can you do some measurements with 16 bit source material ( with output resolution to 24 bit in the Wiim menu ) , no fixed sampling frequency output , volume control used and spdif out ?

Digital volume control using spdif at 100, 80, 60, 40, 20, 10 and 1 ?

The recent measurements were provided by @erazortt who I am sure will oblige if you ask him nicely