Nice, some measurements with these.
Looks like rtings uses an adjusted Harman Target (2017) for their compensation which calls for a 10dB bass boost and DF for the treble regions. The nice thing is that you can quickly convert this over to the DF normalization (something similar to what an Etymotic would be based off of). Granted it's more of an old school compensation, but it shows a lot of what Apple was targeting. I've adjusted the bass for the DF normalization below at some points and connected them: 3 points < 20, 20, 30, 40, ~58, 80, 100, 200. Everything after the ~200 regions is clean for DF since they use DF for everything past this point.
The right earphone looks to be having a worse seal if you look below 20Hz, though it doesn't make that big of a difference, the midrange also looks a little wonky. I drew a line at max(left, 20 Hz, 4kHz) + max(left, 20Hz, 4kHz) / 2. What does this show? From 20 Hz all the way through 4kHz, the AirPod Pros are within 2.5dB from DF neutral. More specifically, < 2k the response is about 2.5dB above that line (except for the dip at 1k) and above 2k, the response is about 2dB below that line once you hit 5k with strong spikes through to the 10k range. If they had evened out the spikeyness > 4k Hz, removed the large increase at 10k and average it out, you'd actually get something
very close to the Etymotic target curve. I know there was a blog post (don't remember the source) that talked about how Etymotic originally targeted DF then found out that treble was too harsh with DF due to loudness in recordings. They lowered the treble response in their originals in twice as they were trying to get it right. This resulted in 3 IEMs, the ER-4B, ER-4S, and ER-4P which were released in that order. There curves can be seen in
Rin Choi's blog.
The Harman target has really taken the audiophile community by storm in the past 5 years and with good reason, it helps further mask out the recording issues (due in part to the loudness wars) that Etymotic battled years past. Etymotic tried to do it by reducing treble, Harman does it by increasing bass. The end goal is to remove those elements of the recording that are "harmful" to the enjoyment of music while maintaining everything else. The Harman curve gets close to this and does it pretty well. That being said, Apple has never really targeted the Harman curve in their IEMs. Their ADDIEM were remarkably very close to DF like the APP are.
) in the sound, typical on high details like hi-hat/cymbals.
)
