GPD Pocket 4 Speaker DSP: Configuring PipeWire so laptop speakers sound better

I couldn't find any mentions of what audio codec it uses in an initial search, but I see "HD Audio" and other sources online say it's a Realtek, so this seems to be a standard Intel HD Audio codec. What's lesser-known is that most if not all of them have a built-in EQ function which can be used to accomplish this (and perhaps the original vendor's Windows drivers already do), but it's not well-documented. Linux has some code for that too (search for EQ in here):

https://raw.githubusercontent.com/torvalds/linux/master/soun...

It's an AMD platform, so it's the native AMD HD Audio Controller (17h/19h/1ah), with a Realtek ALC245 codec behind it. I have no idea what other hardware is involved, presumably an external Class-D amplifier IC (but I don't know as there doesn't seem to be a datasheet for the ALC245 available).

Note, this is not all about EQ. A lot of other techniques are also used, e.g. limiter, exciter (to shift the energy from mid to low), and some psychological tricks to make you believe it's making a fat bass sound, etc.