I will try to be very specific: I have an AAC 256-bitrate file purchased from iTunes ; it's one of a bunch of files in the performance of Elliott Carter's Clarinet Concerto, recorded digitally in 1999 and offered, presumably, as a well-encoded AAC on iTunes.
Here's the problem: the clarinet -- which is almost a square wave in its core sonic signature -- sounds fine soloing at mid volume level, but if there is a sustained note at either really low volume, or a sustained note at peak volume, I hear this "warble" in the note that sounds (to me) annoying and unrealistic.
It's less obvious played through a set of warmer headphones than through a set of IEMs. It is more noticeable at higher volumes, and at the louder, high-pitched sustain note.
I've since noticed, perhaps sensitized by this, similar warbliness (it's almost like old analogue tape flutter) in high-volume, high-pitched sustained notes in, say, operatic soprano singing.
It seems entirely absent in non-classical iTunes music. Which is the thing that confuses me.
It sounds a little bit as if an LFO (low frequency oscillator) had been applied to the note to modulate its volume (not pitch).
I also sometimes notice this warble in the noise floor of quiet analogue passages, what would, pre-lossy-compression, simply have shown up as hiss.
Does anyone have a good, technical explanation of what's happening here? It only seems to show up on some instruments, particularly the clarinet, and sometimes horns, and sopranos, in classical recordings purchased from iTunes.
Has there been sloppy encoding, or is this just an unavoidable artifact of lossy compression, even with 256 AAC? Or is it in the IEM itself, some kind of induced in-ear-canal resonance produced at certain frequencies by a balanced armature driver?
Any true insight would be most welcome, thanks in advance!
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