Bluesound NODE2 to connect to Phantom

[Pleyel]

You can play down to -48 dB and loose no information from a 16-bit CD.
Right?

Hi, Pleyel.
This is wrong, with improbable exceptions.
There is no way to tell the DAC to reduce volume (unless you . DAC doesn't do volume control, the amplifier does.

If you are not changing the amplification in the amplifier, then you want the output from DAC to be lower level.
Signal from DAC is always output at same absolute levels. So if you want reduced levels you need to start zeroing some of the bits.

If your source upconverts your 16bit stream into 24bit and then applies the gain, you may really be ok until -48dB, but most consumer equipment does not upconvert audio signals, and if it does, upconversion and gain is not done with high precision, thus adding noise to the signal. Most equipment when given 16bit signal will just forward that as-is. A 24-bit DAC will accept a 16bit stream fine, and reconstruct it with appropriate dynamic range for 16bit. If only 10bits of those 16bits are used, the dynamic range resulting will be that of 10bit signal. The amplifier will then amplify whatever signal the DAC outputs, and, as a side note - most amplifiers respond much worse (higher distortion) close to their maximum than at lower levels. So you lose fidelity by reducing bit-depth or gaining noise during upconversion/neg-gain in the source and possibly lose fidelity again by driving the amplifier at it's maximum, amplifying maximally the reduced noise floor.

Just as a reference, read this paper by ESS regarding digital volume control, but note that the solutions mentioned are not applicable if you reduce bit-depth at source, as the data path between the source and the DAC is limited by the optical interface, through which you HAVE to send the zeroes, to attain the volume-control effect. So the DAC never sees the original data, just zeroes, so there's nothing that can be done to repair the signal.

http://www.esstech.com/files/3014/4095/4...ontrol.pdf
TLDR: First couple of slides (1-9) is what happens when you apply volume control at source.

Hi iliapa,
I respectfully, yet fully disagree, but will need more time to explain a little later.
Difference between resolution and quantization noise will need to be addressed.
I really confirm that lower resolution streams are LSB-padded to operate higher resolution DAC at full scale (wherever in between). This extremely simple operation is even not called upsampling, but part of the interfacing. Non power-of-2 gains are another story, as pointed, but do not impact resolution before -48 dB: they add in-band noise if no dithering is applied. The paper does not address the case of 16-bit music into 24-bit DAC, which specifically provisions 8 bits for attenuation.
More to come when I can.

PS: On another subject, h_u_g_e kudos for your Phantom protocol deciphering.