I didn’t believe the difference would be noticeabe (or that my ears would notice) until I replaced my HifiBerry hat with a very affordable Topping D10S, but the improvement was obvious and significant.
You will be back at square one, S/PDIF does not have hardware volume…
But Bluesound Node digital RCA can use Hardware Volume as far as I know…
Where did you read that? Link?
My brother owns one and is using it with RCA digital for connecting hypex active LS that way
Okay. I still don’t.fully understand. The USB Dac would be working as the port has a mixer that can be controlled by Volumio? If that is the case why do I need an additional DAC as I convert in the Hypex Module anyway? Would be an USB Coax/SPDif adapter suitable?
Thank you
Andreas
the S/PDIF is a very old standard protocol, it does not allow to send values and/or commands for volume control to the receiver side.
If the Bluesound Node has volume control capabilities on the S/PDIF interface, it means the output stream is sent already attenuated to the receiver. Thus, it is a SW volume control, not an hardware one. You can obtain the very same result enabling SW volume control on Volumio.
I thought that the DAC is changing the volume information in the digital output. Like an EQ on all frequencies. But I obviously have no clue. 
So a software volume control…
Also think, that in order to control the volume on S/PDIF, the digital (RAW) signal needs to be converted to PCM first.
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I’d like to elaborate a bit more on what I claimed before, with a high-level explanation on how HW volume control works
-
When using a I2S DAC with Hardware volume control
** the audio stream is sent “as-it-is” to the DAC via I2S interface, so bit-perfect / full-scale at 100%
** the volume value is sent by the linux driver via I2C interface to the DAC, and the DAC makes use of this value to adjust the level of the analog output ath the very end of the signal chain -
When using a USB DAC with Hardware volume control
** USB is a universal interface, it can be used for different things, also simultaneously
** the audio stream is sent “as-it-is” to the DAC via UAC protocol, so bit-perfect / full-scale at 100%
** the volume value is sent by the linux driver to the DAC via HID or similar protocols, and the DAC makes use of this value to adjust the level of the analog output at the very end of the signal chain -
When using a S/PDIF interface
** S/PDIF is a very old standard protocol, with well defined structure for the data.
** The S/PDIF protocol does not have the volume/attenuation information in the data structure
** It’s not possible to send the volume value to the receiver DAC, to be used for HW volume control as done for I2S and USB.
** if it’s possibile to have volume control on the Bluesound Node connected via S/PDIF, it means the audio stream is sent attenuated (so it’s manipulated, not bit-perfect) to the DAC, because it’s not possible to do otherwise.
Hello Dario,
thank you for the summary. What happens when I use a digital RCA or SPDIF out on the USB DAC? Can that be controlled by the Volumio hardware mixer?
Best
Andreas
if the output is a digital S/PDIF signal, it is not a DAC (digital-to-analog converter), but a digital-to-digital converter
even if you can control the volume of that device via volumio, the output will be a manipulated (attenuated) digital signal, basically exactly what you will get with a Hifiberry DIGI with software volume control.
I would suggest you run some tests to determine if you can actual hear that SW volume control is used.
We all try to do everything or, strive, bit perfect, but to be honest I don’t think there is a person in the world who has actually heard it. As every bit perfect stream needs to become analog for us to hear.
Good idea. I will try to do so. Thing is that I am now happy that I have a (perfect) digital signal from Network/CD to the DAC,Amp,DSP,Crossover in my self build active LS. Hypex FA123 (and 122 modules in my office). No needless multiple conversions. People pressing MQA or other digital studio on LPs. High End Phono Equipement making digital output of this very basic analog information. :).
I use quite decent chassis (Satori). And there is a very, very huge difference between this new setup and my old NAD AMP / 1500 EUR bought speakers before. I had the new self build LS running with analog input from the NAD amp and it was way worse. So it is not only the speakers. It is the chain that makes the huge improvement. Thus I could imgagine that I hear some difference
I use the DSP volume in Roon solves that problem for me, its converted to 32 bit priolr so no dynamic loss form attentualtion. Im runnong a passive preamp now from the output of the Protodac no gain and manright into the XTZ REDGE A2-300 sounds superb compared to my tube pre.
little snippet from my Yputube channel.
Maybe this could be interesting to you.
If there was a virtual mixer available that would do all the gui part of volume control, disregard the final step of actually changing volume.
An extension could be an IR mixer that added the IR control to the end of the gui volume control.