This is how Apple addressed audio hardware and do something similar for speakers. Instead of trying to make speakers that have the desired frequency response or microphones that produce the desired signal, they let the analog hardware do whatever it does.
Then in software they use digital signal processing. For speakers they modify what gets sent to the hardware so that the actual output then does match the frequency response, and for the microphones they do this work to extract the desired signal.
If Linux addressed the speakers as is, you would get unpleasant sound, and if it read the microphones as is, it would get a lot of noise. That is why Asahi had to add digital signal processing to the audio input and output, to get the "correct" audio.
It does mean the processing is specific to the analogue audio hardware in each of the different Mac models.
The processing could be done in additional hardware, but why bother when you have a very good CPU that can do the work.
> For speakers they modify what gets sent to the hardware so that the actual output then does match the frequency response
As I understand, this is not a magic pill: it probably won't help to pull out frequencies which are suppressed by 30-40 dB and I assume that if the frequency response graph is too wavy (lot of narrow peaks and dips), it won't help either.
Also, you need to have calibration files to use this method, right?
Yes you need calibration files for supported models. You can see the details and explanation at the asahi audio repository. They also criticize the MacOS curves, and point out how some Windows vendors are doing the same DSP approach.
By the way I now realized that simply adding an equalizer before the amp might be not enough; speakers typically produce different sound in different directions, so for a perfect sound you need to somehow track location of the head and adjust filter curves.
Interesting, does that means Mac speakers may be great for certain sounds, but not others.
I mean, Apple uses high quality speakers to begin with, as far as laptops go. I'm sure they're not making 40 dB corrections, that would be ginormous.
Yes, I would be very surprised if they weren't using specific calibrations for each model. That's pretty basic.