I’m using RoPieeeXL to a Benchmark DAC3 via USB.
I’ve noticed that the DSP volume is actually in the RoPieee side, but I was expecting that it was on the Roon side, alongside with DSP convolution and volume levelling.
If I select Device Volume I’m getting an Enhanced audio path, but I’m not really clear where the “Hardware” part is taking place. Someone can explain it to me?
I’ve also noticed that in RoPieee config, it states that “hardware mixer is not supported”. How does this work? Is it the hardware mixer used only for Roon, or it’s not supported from the DAC? If the later, what does “Device volume” mean in Roon?
This is the mixer status:
Simple mixer control 'Benchmark DAC2 Audio 2.0 Output Playback Sw',0
Capabilities: pswitch
Playback channels: Front Left - Front Right
Mono:
Front Left: Playback [on]
Front Right: Playback [on]
Simple mixer control 'Benchmark DAC2 Audio 2.0 Output Playback Sw',1
Capabilities: pswitch pswitch-joined
Playback channels: Mono
Mono: Playback [on]
Simple mixer control 'Benchmark DAC2 Audio 2.0 Output Playback Vo',0
Capabilities: volume
Playback channels: Front Left - Front Right
Capture channels: Front Left - Front Right
Limits: 0 - 127
Front Left: 127 [100%]
Front Right: 127 [100%]
Simple mixer control 'Benchmark DAC2 Audio 2.0 Output Playback Vo',1
Capabilities: volume volume-joined
Playback channels: Mono
Capture channels: Mono
Limits: 0 - 127
Mono: 127 [100%]
Hardware mixer support is only supported on HAT’s.
And this is for XL services only (it is on the XL tab).
Roon/RAAT takes care of things when you’re doing Roon.
Wrt to your earlier remark:
Roon’s DSP volume is on the server side. There you have the power to do the calculations to make that possible.
@spockfish thank you for you answers!
So, in terms of sound quality, the best solution would be to use Roon using DSP volume, and with this setting calibrate the system to 75/77 db SPL with Pink Noise full range -20db using the DAC’s volume? Or is preferable to use Roon’s Device volume?
That is one is always tricky.
It highly depends on how the volume control is implemented on the DAC side. Is in in the analog domain? Then I suggest you go for that route (general rule of thumb: analog volume control is better then digital volume control).
If it’s digital (which I suspect in this case) I tend to choose Roon: purely because it’s done in software, on a powerful platform (your Roon server) and thus is more advanced than the digital in your DAC.
But then again… 
Thanks!
FYI this is an excerpt from the DAC3 instruction manual Page 6:
“The HGC system uses an active analog gain control for analog inputs and a 32-bit dithered volume
control for digital inputs. Both types of inputs leverage the low-impedance passive analog attenuation system at the XLR outputs.
The dual-domain HGC system combines the high dynamic range of Benchmark’s HDR analog control (used in the DAC1 HDR) with the low distortion and accuracy of a digital control. HGC outperforms traditional analog or digital volume controls, including the two- stage DAC1 HDR system. Musical details are preserved over a very wide range of output levels. Analog inputs are controlled in the analog domain. Digital inputs are controlled in both domains.”
@spockfish I’ve found this explanation from the Roon Hardware team on the DSP volume Device volume control
It seems that the DSP volume is done on the endpoint and not on the core, therefore requiring another 24bit -> 64bit -> Volume -> Dither to 32/24bits process. I’m not sure if this double volume levelling (i.e in core for the LUFS and in the endpoint for final volume) is compromising the sound quality. If I’m needing a fixed volume control (e.g. -5dB, which is what I need for 75db FS with the DAC at unity gain), would it be better to set the LUFS to a relative -5?