To me it is very easy to tell warmth to neutral in sound signature. It comes down to digital music in basic and it principles.
1/ digital musics and files with multi-bit and PCM such as WAV, FLAC, needs algorithms and DSP to come into a DAC which convert by Sigma-Delta system and come out as Analog signals. The implementations and designs around this architecture will affect the outcomes.
2/ DSD files is a 1 bit direct stream. It was called direct stream because it can no longer be processed and Add or subtract, or losses any informations any further. It only comes to the high-pass and low pass filter before being amplified. This is the end of it chain, the analog output.
So, having a file of the same track which is FLAC and then compare to the same FLAC but is processed by Xivero or HQplayerPro to DSD. You will expose 2 different situations
A/ FLAC being processed with DSP and algorithms of the DAP maker
B/ DSD processed by your PC.
The DSD is the most neutral one because it is offline converted by the algorithms itself. Even if different programs and algorithms is using different Sigma-Delta Modulators, it shouldn’t be too different from neutral. The most trust worth algorithms are HQplayerPro and Xivero, but with HQplayerPro, you can tinker around the algorithms, you choose what DSP you want and or pure Delta-sigma modulator only. I chose HQplayerPro and referred to the DSD file as Neutral. I also deemed it Neutral because I compared the same FLAC and using different software algorithms, and the HQplayerPro on the same player is always more neutral.
Now, with all of that out of the way, a FLAC and DSP by the Manufacturers will sound significantly different than an offline DSD processed FLAC, and there are many reasons for this. So, if the FLAC has a lot of warmth ? That means the DAP itself is warmth....if the FLAC itself is similar or close to the DSD, then it is neutral......and if it is brighter than the DSD then it is a brighter DAP. Period
Yes, I understand sound is subjective , but there is a limit guide lines to everything, and this is what I used and deemed something to be neutral