16 bit PCM upscaled to 32 bit Mystery

Core Machine (Operating system/System info/Roon build number)

Intel i7 Kaby lake Windows Server 2016 Roon 1.8

Network Details (Including networking gear model/manufacturer and if on WiFi/Ethernet)

Etherregen Switch

Audio Devices (Specify what device you’re using and its connection type - USB/HDMI/etc.)

I have a Roon connected to an Esoteric N-03T via EtherRegen switch. N-03T is connected by USB cable to an Accuphase DC-950 DAC

Description Of Issue

I have no problems with DSD but all PCM is output at 32 bit irrespective of whether it is 16, 24 or 32 bit source. ( Accuphase DAC reads actual frequency and Bit depth of of the incoming signal). It is not the Esoteric causing the problem because it faithfully transfers audio streams from an attached USB drive without alteration.

I am not a fan of upscaling with this DAC and I simply want to play PCM as it was recorded and not changed in any way. Does anyone have any idea what could be causing this?

Bit-depth is not like sample-rate conversion (where actual interpolation of sample points is required). “Converting” 16bit to 32bit just means padding by zeroes — an operation which has absolutely zero effect on anything except the bandwidth used to transmit the data.

(In fact, if you check the Signal Path, I think you will find that Roon has — at an intermediate stage — converted to 64bit-float, which is where it does all of its operations.)

Thanks Jacques. I assume the zeroes would be added in case someone wanted to use software volume control ?

The reason is dumber than that. As I said, at an intermediate stage, Roon converts to 64-bit float. If you do any DSP, those manipulations are done at that stage. The result is then converted back to integer at the highest bit-depth accepted by your DAC (32bit, in the case at hand),

If you don’t do any DSP (including volume-leveling or headroom management), then the net effect of 16bit → 64bit float → 32bit is just to pad each original 16bit sample with zeroes.

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