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Topic: All about bluetooth audio (Read 2219 times) previous topic - next topic
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Re: All about bluetooth audio

Reply #1
yes that was an interesting read.

Re: All about bluetooth audio

Reply #2
thank you for the link, I certainly learned a lot.

Re: All about bluetooth audio

Reply #3
Thanks, that was good. This statement jumped at me cause I've been thinking that the Roku Ultra 2016 (and maybe all Rokus?) does something like this for DD+:
Quote
When listening to music in AAC format, it is first decoded by the OS, then encoded into AAC again, for transmission over Bluetooth. This is necessary to mix several audio streams such as music and new message notifications. iOS is no exception. You can find a lot of statements that iOS does not transcode music in AAC format for transmission via Bluetooth, which is incorrect.

The Roku outputs to DD+, for example Netflix content which is also in DD+, but I haven't seen mentioned anywhere that it must be reencoding into DD+, because the menu sounds are mixed into the audio as well. The Apple TV 4K in contrast, outputs in LPCM as expected.

Re: All about bluetooth audio

Reply #4
Thanks for the link. It's a very good article. A wealth of information collected on just one site.
marlene-d.blogspot.com

Re: All about bluetooth audio

Reply #5
I'd be slightly more impressed with that link if it wasn't suggesting that you subtract the encoded and lossless versions of files and check the low pass frequency cutoff to determine audio quality. 

Re: All about bluetooth audio

Reply #6
I'd be slightly more impressed with that link if it wasn't suggesting that you subtract the encoded and lossless versions of files and check the low pass frequency cutoff to determine audio quality. 
The article does not suggesting that. There's only a spectrograms of already encoded files, without the subtraction.
And there's no low pass filter in SBC. It just utilizes available bitpool from lower to higher frequencies. If bitpool is not enough for high frequencies, they won't be encoded. But they are not getting cut off on purpose, but some filter.

You can use spectre subtraction to see the difference between original and encoded audio with simple codecs like SBC or aptX if you want. While you won't get any proper results with complex psychoacoustic codecs like MP3 or AAC, you can use this method for non-psychoacoustic codecs.

Re: All about bluetooth audio

Reply #7
I also created the patch for Android to improve audio quality on SBC codec. It's merged into LineageOS alternative firmware, but I want it to be merged into mainline Android. You can help by leaving a star (top left icon) in this feature request at Android public bug tracker: https://issuetracker.google.com/issues/136342164

Re: All about bluetooth audio

Reply #8
I'd be slightly more impressed with that link if it wasn't suggesting that you subtract the encoded and lossless versions of files and check the low pass frequency cutoff to determine audio quality.
Here is more elaborated method to determine audio quality of SBC XQ [http://soundexpert.org/articles/-/blogs/audio-quality-of-sbc-xq-bluetooth-audio-codec]. Its quality is on a par with aptX HD.
keeping audio clear together - soundexpert.org

Re: All about bluetooth audio

Reply #9
I'd be slightly more impressed with that link if it wasn't suggesting that you subtract the encoded and lossless versions of files and check the low pass frequency cutoff to determine audio quality.
Here is more elaborated method to determine audio quality of SBC XQ [http://soundexpert.org/articles/-/blogs/audio-quality-of-sbc-xq-bluetooth-audio-codec]. Its quality is on a par with aptX HD.
> ... 328 kbit/s (44.1/16) for high quality mode. This mode provides just acceptable audio quality according to SE ratings.
so, according to these ratings, SBC@328 is already transparent, if that's true then what's the point of increasing bitrate?

Re: All about bluetooth audio

Reply #10
> ... 328 kbit/s (44.1/16) for high quality mode. This mode provides just acceptable audio quality according to SE ratings.
so, according to these ratings, SBC@328 is already transparent, if that's true then what's the point of increasing bitrate?
While the overall rating is 6.14 (with 10% accuracy), one of nine SE sound samples has only 4.5 score. So, there could be some other samples that have 4.0 rating or even lower. This is definitely not already transparent but just acceptable audio quality and some quality margin will be helpful.
keeping audio clear together - soundexpert.org

 
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