Something I’ve always wondered about lossy audio compression like AAC, MP3, ATRAC, and the like.
Is it possible to have a high enough bitrate such that you are guaranteed to lose nothing?
From my understanding of how most of these work, you take an input signal, and then transform it into another representation, then prune away parts that the listener will likely not notice (this decision based on sophisticated modeling of how human’s percieve sounds).
Is it such that, in order to be able to reproduce the original input signal completely, the resulting stream of one of these algorithms would need to have the same bitrate as it took to generate the original signal? I mean, for most mp3, ogg, encoders, I can’t tell the difference between 320kbps encodings and the original full WAV encodings. Granted, I might not have the most rediculously accurate and high fidelity listening setup in the world, but still, I consider my ears to be more sensitive than many others I know. Isn’t it the case that a 512kbps mp3 or AAC could actually represent the original signal? or does it just not work that way?
I wonder because, you look at the lossless format, and realize that in fortunate cases, you can shave 50% of the data without losing a single bit. That means in the PCM represntation space, half of the data is actually redundant. Can you shave off this ‘half’ by using any other encodings?
This is really in relation to a post I wrote earlier about the ideal iTunes/iPod functionality, where your PC stores high-bitrate versions of files, and they get automatically converted down to lower ones when you put them on the iPod (to save space). If you want to keep original cd-quality data around on your PC, it makes such a scenario difficult, since you’d have to do a real conversion from ALAC to AAC each time, not just shaving some bits off of the AAC signal.
But then again, maybe the whole thing is moot. These UE in-ear monitors have really changed my expectations in terms of what I’ll be able to hear when I’m on the road. They totall put my car’s stereo system to shame balance-wise. Even the Beatles CD’s that I’ve listened to hundreds of times, I’m noticing new things when they come through the UE’s from the iPod. So maybe wanting low bitrate on the iPod is just pointless. It’s probably better to just wait around for storage technology to get good enough so that it just doesn’t matter.