ah my bad, I misinterpreted your comment to mean "it has a DAC, so it can use DSP".

But what you said was that since the USB-C connection can be digital, this allows to put digital devices (like a DSP) in between the USB connector and the analog connection to the headphone.
Which is correct of course.

to companies that specialise on that aspect of product design.

> Well it being a type C version would mean that it has its own DAC, allowing them to DSP correct to whatever FR they want.

a DAC doesn't necessarily have DSP capability. You would need a dedicated IC for that.

> does moondrop have experience in this sort of field?

These things are easily (and commonly) outsourced.

> First i tought most people would rather have bassy gear like Bose or Beats.

Most people buy after the brand name, not after sound quality - even though they sometimes follow what they think a certain brand promises in sound.
Few people are save from that - yourself (no disrespect to you, I'm sure you are a good listener) being not excempt either: Both Bose and Beats have made bass-light products! Yet the myth that "bose = bass" and of course "beats = bass" persists (not entirely unfounded eiher of course)

> A quick search showed me that the most sold earpiece was apparently the airpods (i couldn't fact-check), which have a treble bias.

Most likely not because of sound quality though, but because of the ease of use and also the brand name, as you said yourself:

> To me it only show that people react more to brand recognition and/or to the "fashion" element of their gear.

> But whether most people would rather want unbiased gear or not is left to be proven.

There's been quite a lot of research on that matter actually, plenty of controlled listening tests having been done with different ways of formulating essentially the same question: Do people prefer unbiased/"good"/neutral/uncolored sound, or have they gotten used to something else?
In general, most research (that I'm aware of) does in fact point towards the average person preferring what would be considered "good" sound (neutral, uncompressed, uncolored, ...) - as long as they're given the option.

> neutral sound means that all frequencies are perceived at the same volume. i.e the sound doesn't lean toward one nor in the other direction.

That's exactly it though - you get a rotary button to control the amount of bass, and you get asked to dial it in until it sounds correct, as in "it sounds the way it should sound".
You repeat this with many, many people go get a meaningful average.

"neutral" does not mean "flat on a measurement".

> Harmon, Ief neutral,. .. can be thought as some widely popular neutral colors like Navy and khaki.

That comparison falls flat, because the question is not "tell me a neutral color" (for colors) or "tell me a neutral amount of bass" (for sound).

The question that the research answered was: "here's a control wheel, dial in the amount of bass that sounds correct while listening to music".
Which is the equivalent of: "here's a control wheel to control the amount of yellow in this picture of a sunflower, dial in the amount of yellow until it looks correct to you".

> it still isn’t neutral because the bass and treble are amplified.

That's hypothetical, because the preferred sound of most people is not V-shaped (when given the option).

The word "neutral" comes from latin "ne utrum", meaning "neither of both".
In this context it refers to "neither too little nor too much".

If the average person (in a properly conducted listening test, which is hard to do) prefers a sound, then by definition it is neutrum, meaning it leans neither in one direction nor in the other direction.

> Is there a headphone that is lighter than the NDH30 but perform similarly?

HD560S :) (in terms of bass extension. It's quite a bit brighter than the NDH30 at the top, which in this case is a good thing since that's where the NDH30 is lacking)

> Or most people, honestly

By definition, "neutral" is what most people want. "neutral" meaning "neither of both", as in "neither too little nor too much".

they're all open-back. Out of the box I prefer the HD560S, they come the closest to what I consider neutral sound, at least out of those three. But when using them with EQ, those differences become miniscule.
However in terms of comfort, the NDH30 and DT900X both beat it, the HD5xx-shape just doesn't completely fit my head.

Nice. These are enormously comfortable. A tad brighter than the DT880, and generally an improvement. Very easy to EQ!