For context, LDAC is one of the few wireless audio codecs stamped Hi-Res by the Japan Audio Society and its encoder is open source since Android 8, so you can see just how long Windows is sleeping on this. I'm excited about the incoming next gen called LC3plus, my next pair is definitely gonna have that.
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I definitely love it for the "it just works" (or rather, you have full control to make it work) factor!
I'm not familiar with the latest in BT audio, but isn't the standard still sub-par in that it has very limited overall frequency bandwidth, resulting in deep sacrifices to fidelity?
I recall a detailed analysis of different BT audio codecs a while back, and the spectrum analysis always showed relatively high noise floor and frequency roll-off (hi-cut/low-cut) within the threshold of human hearing (though admittedly close to the limits). Also, I recall (and this could just be the 2016 tech I am familiar with) that overall bandwidth was limited in that if you played something with low frequency tones, the upper frequencies were dropped, or vice versa. I used to confirm this by using a flat EQ setting, then boosting any range, and you could easily detect the loss of frequency response in the adjacent or distant ranges.
Is this a thing of the past now?
No, soundguys made an anlysis. LDAC is still worse than direct contact and just makes some other sacrifices than aptX.
It is worse than uncompressed, but 990Kbps LDAC is the closest codec to totally transparent I've heard for Bluetooth audio. AptX HD is nearly as good to my ears, and is better than 660Kbps LDAC. The differences are very small though, especially when compared with the differences on the analog side, e.g. the amp, and particularly the headphone design.
Apple side-steps the problem by, at least when you're listening to Apple Music, simply sending the AAC stream as-is to the headphones and has them decode the audio. I don't know why that isn't a more common approach.
I'm still somewhat bemused that we're talking about Bluetooth codecs at all. It surely can't be that difficult technically to get 1.5Mbps actual throughput on Bluetooth and simply send raw 16-bit/44.1Khz PCM. 2.4Ghz WiFi is capable of hundreds of times that speed. Bluetooth has been stuck at the same speeds for decades.
Do they actually though? Everything I can find says that's just a myth. If it can play multiple things at the same time, they can't possibly do that.
they dont. this is a myth. it's more or less incompatible with how bluetooth works, sure it could be kind of possible, but reliability would be out of the window
I could well be wrong about the AAC passthrough, and I should have hedged that statement with "allegedly" as I've not tested it myself.
To your other point though, I disagree - there are plenty of ways you could pass through an unchanged AAC bitstream, but still mix in other sounds when required. For example, having the sender duck the original bitstream out temporarily and send a mixed replacement bitstream while the other sound is playing. Or (and this would only work if you control the firmware on the receiver, but if you're using Apple headphones with an Apple device, that's not a problem) sending multiple bitstreams to the receiver and letting the receiver mix them.
this isnt even correct, AAC beats 990kbps LDAC, aptx-HD and SBC-XQ matches or beats 660kbps (which is normal listening usecase).
however even after all of that, SBC-XQ, AAC, LC3Plus are all audibly transparent to the vast majority of people at normal listening bitrates with the major difference being vendor tuning
I can only comment on my experience with my own equipment and ears, but in my experience, 990Kbps LDAC is noticeably more transparent than 256Kbps AAC for Bluetooth audio.
I can fairly reliably guess whether or not I remembered to switch my Sony XM4s out of multipoint mode the last time I used them (when in multipoint pairing mode LDAC is not supported and 256Kbps AAC is usually what gets negotiated). The difference is small, but over a few minutes of listening, the sonic signature when it's using AAC is just a little bit "off" and my ears don't like it as much.
Could I ABX the difference using the usual ABX setup with short samples of music I'm not familiar with? Probably not. Can I tell the difference over an extended period using music I know well, and that I often listen to uncompressed? Yes, pretty easily.
LDAC is not a particularly sophisticated codec, but it doesn't have to be when it has a 990Kbps bitrate. It's also possible that the FDK-AAC codec that I think both Pipewire and Android use for real-time AAC encoding is not the best tuned for 256Kbps CBR. AIUI in 256Kbps CBR mode, FDK-AAC has a hard low-pass filter at 17KHz, and I can still hear above 17KHz.
if you tested on android then I wouldn't be surprised, android is notorious for having sketchy AAC settings https://www.soundguys.com/the-ultimate-guide-to-bluetooth-headphones-aac-20296/
FDK-AAC on linux is considerably better, I dont think I did a bitrate mod on it but I may have? I think pipewire by default caps AAC at 320kbps and can hold it reliably, and at 256k both opus and FDKAAC are transparent to the vast majority of people even on high end audio setups.