It happens on some songs. Not all. Also, not only on songs.
I can't remember a specific example, but hear this:
Are you familiar with the situation when sometimes you hear a song, then you play an Instagram video simultaneously, and the IG lowers the music's volume?
Now let's say that this specific IG video is silent in most of it, so it results in a low volume music + low music video (because the video lowers the music volume). When it goes below a certain threshold (too low), the iPhone speakers will reduce the volume even more, and on the moment the IG video will have a louder part, both the IG video and the Music will jump up in volume.
Every time you hear something that's below a certain threshold, the iPhone will reduce the volume and filter it - and jump back up when the audio source passes the threshold again.
It has nothing to do with the music dynamics or anything like that. If you have a new iPhone (or a new IOS version, because I believe this is not a hardware but a software issue) you have to notice it on certain occasions, and if you don't, well, I don't think it helps when you keep trying to show people how this issue doesn't exist (I saw this behavior on some of your comments), because it DOES exist, and you clearly just don't have the ears to notice that, although it's pretty noticeable.
You can try listening in full volume to songs like: "IU - Love Poem" (volume jumps up the moment she starts to sing), "LeeHi - HOLO" - (Also jumps up when she starts singing), "Alan & JJ & May Twik - טאק בום בום" It's in hebrew but you can find it on one of the artists' pages (All the start jumps up and down in volume, and you can clearly hear the bass sound coming back to life when all the other instruments come in on 0:08).
Try hearing those songs on speakers of an iPhone that has the latest IOS version (optimally iPhone 17) and then hear it on your PC or connect the phone to a Bluetooth speaker. You'll immediately hear the difference.
Honestly, I can't believe this is still going for so long and Apple didn't fix it.
