iPhone AAC vs. Aptx and Aptx-hd real world
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pstickne

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https://habr.com/en/post/456182/

I don't know enough to say if everything in this article is correct, but the little I know seemed to align.
it certainly is very informative.
Thanks for the link, it is great consolidated reading!

And this makes me :anguished::

"AAC has many extensions to the standard encoding method. One of them—Scalable To Lossless (SLS)—is standardized for Bluetooth and allows you to transfer lossless audio. Unfortunately, no SLS support could be found on existing devices. An extension to reduce transmission delay AAC-LD (Low Delay) is not standardized for Bluetooth.", so much more could be had.

"The situation with AAC is ambiguous: on one hand, theoretically, the codec should produce quality that is indistinguishable from the original, but practice, judging by the tests of the SoundGuys laboratory on different Android devices, is not confirmed. Most likely, the fault is on low-quality hardware audio encoders embedded in various phone chipsets. It makes sense to use AAC only on Apple devices; with Android you'd better stick with aptX/HD and LDAC."

And some article conclusion :anguished::

"People who do not hear the difference between codecs while testing via a web service claim they hear it when listening to music with Bluetooth headphones. Unfortunately, that is not a joke or a placebo effect: the difference is really audible, but it is not caused by difference in codecs."

"The marketing of alternative codecs is very strong: aptX and LDAC are presented as a long-awaited replacement of the “outdated and bad” SBC, which is far from as bad as it is commonly thought of." .. "As it turned out, the artificial limitations of Bluetooth stacks on SBC can be bypassed, so that the SBC will be on par with aptX HD."
 
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SergeSE

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According to my recent research SBC at high bitrates (SBC XQ) is on a par with aptX HD.
 
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SVO

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"Most wireless audio devices have a maximum bitrate of 320 kbps for AAC, some support only 256 kbps. Other bitrates are extremely rare.
AAC provides excellent quality at 320 and 256 kb/s bit rates, but is prone to generation loss on already compressed content, however it’s difficult to hear any differences between the original and AAC 256 kb/s on iOS, even with several consecutive encodings. For MP3 320 kbps encoded into AAC 256 kbps the loss can be neglected."

As an iOS user who has done some fairly critical testing, this is exactly what I found. ALAC rip to AAC produces output that is indistinguishable from lossless wired, at least for me/most. I could hear degradation on MP3 rips below 320 kbps to AAC.
 
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bigshot

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Generation loss may not be the best way to describe it because the loss all occurs in transcoding from one codec to another. You can encode back and forth from WAV to AAC a whole bunch of times with no loss at all. The trouble comes when you transcode from MP3 to AAC.
 
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