Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

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Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

2022-06-11 19:35:03

Abstract:
Personal blind sound quality comparison of the Bluetooth codec, AAC and LC3, at 160 kbps, at 44.1 kHz(except for liblc3).
As of 2022, Bluetooth earphones and speakers often support AAC codec.
LC3 is a new codec, which will be mandatory in the upcoming LE Audio in Bluetooth 5.2.
Two AAC encoders were tested; one engine is CoreAudio, used by the Apple, and the other engine, FDK-AAC is used by the Android.
Two LC3 encoders were tested; the latest LC3plus encoder available from ESTI, and google / liblc3, which is actively developed by Antoine SOULIER as of June 2022.
The original lossless tracks were first encoded by Opus 128 kbps, decoded, and then re-encoded by the AAC and LC3. This is meant to replicate how online streaming services are used with Bluetooth.
MP3 encoded with LAME CBR was also tested, as anchors. MP3 was directly encoded from the original, not from Opus.

Encoders:
Opus 1.3 via opus-tools-0.2
CoreAudioToolbox 7.10.9.0, via qaac 2.73 (x64 version).
FDK-AAC 2.0.2, via ffmpeg version N-102573-g9d4c018497.
LC3plus Floating Point Software V1.6.3ETSI, ETSI TS 103 634 V1.3.1.
google / liblc3, Apr 20, 2022 version (older version, as of June 2022).

Opus settings:
opus-tools-0.2-opus-1.3\opusenc --bitrate 128 in.wav temp.opus
opus-tools-0.2-opus-1.3\opusdec --float --quiet temp.opus temp.wav
qaac_2.73\x64\refalac64 temp.wav --rate 48000 -D -b 16 -o temp.48kHz.wav
qaac_2.73\x64\refalac64 temp.wav --rate 44100 -D -b 16 -o temp.44kHz.wav

Opus ⇒ AAC Settings:
qaac_2.73\x64\qaac64 --cbr 160 -o out.mp4 temp.44kHz.wav
ffmpeg102573 -y -i temp.44kHz.wav -c:a libfdk_aac -b:a 160k out.mp4

Opus ⇒ LC3 Settings:
LC3plus -E -q -v temp.44kHz.wav out.lc3 160000
liblc3\bin\elc3 -b 160000 temp.48kHz.wav out.lc3

MP3 Settings:
lame3.100.1-x64\lame -b 128 in.wav out.mp3
lame3.100.1-x64\lame -b 64 in.wav out.mp3

Sample tracks:
15 sound samples from Kamedo2's samples.
12 sound samples from IgorC's samples.
Total 27 diverse music and speech sound samples.

Hardware:
Sony PSP-3000 + RP-HJE150.

Results (AAC and LC3 only):

Results (including MP3):

Conclusions & Observations:

AAC offered very high fidelity at 160 kbps. Most scores were better than 4.0 (Perceptible, but not annoying) in this particular situation. So were Opus.
LC3 encoder, provided by ESTI, did not offered fidelity comparable to the commonly used AAC codec at 160k in this particular situation.
LC3 encoder, developed by Google, did not offered fidelity comparable to the commonly used AAC codec at 160k in this particular situation.
It's not clear which LC3 encoder was better from this test alone.
An original track first encoded by Opus 128kbps, decoded, then re-encoded by LC3plus is still better than the LAME MP3 CBR 128kbps encoded once.

Anova analysis:

Code: [Select]

FRIEDMAN version 1.24 (Jan 17, 2002) http://ff123.net/
Blocked ANOVA analysis

Number of listeners: 27
Critical significance:  0.05
Significance of data: 0.00E+000 (highly significant)
---------------------------------------------------------------
ANOVA Table for Randomized Block Designs Using Ratings

Source of         Degrees     Sum of    Mean
variation         of Freedom  squares   Square    F      p

Total              161         132.90
Testers (blocks)    26           7.81
Codecs eval'd        5         114.05   22.81   268.52  0.00E+000
Error              130          11.04    0.08
---------------------------------------------------------------
Fisher's protected LSD for ANOVA:   0.157

Means:

AAC(FDK) AAC(Appl LC3plus  liblc3   LAMECBR1 LAMECBR6 
  4.36     4.35     3.99     3.89     3.56     1.90   

---------------------------- p-value Matrix ---------------------------

         AAC(Appl LC3plus  liblc3   LAMECBR1 LAMECBR6 
AAC(FDK) 0.926    0.000*   0.000*   0.000*   0.000*   
AAC(Appl          0.000*   0.000*   0.000*   0.000*   
LC3plus                    0.227    0.000*   0.000*   
liblc3                              0.000*   0.000*   
LAMECBR1                                     0.000*   
-----------------------------------------------------------------------

AAC(FDK) is better than LC3plus, liblc3, LAMECBR128kbps, LAMECBR64kbps
AAC(Apple) is better than LC3plus, liblc3, LAMECBR128kbps, LAMECBR64kbps
LC3plus is better than LAMECBR128kbps, LAMECBR64kbps
liblc3 is better than LAMECBR128kbps, LAMECBR64kbps
LAMECBR128kbps is better than LAMECBR64kbps


FRIEDMAN version 1.24 (Jan 17, 2002) http://ff123.net/
Friedman Analysis

Number of listeners: 27
Critical significance:  0.05
Significance of data: 0.00E+000 (highly significant)
Fisher's protected LSD for rank sums:  26.945

Ranksums:

AAC(Appl AAC(FDK) LC3plus  liblc3   LAMECBR1 LAMECBR6 
143.00   141.00    98.00    87.00    71.00    27.00   

---------------------------- p-value Matrix ---------------------------

         AAC(FDK) LC3plus  liblc3   LAMECBR1 LAMECBR6 
AAC(Appl 0.884    0.001*   0.000*   0.000*   0.000*   
AAC(FDK)          0.002*   0.000*   0.000*   0.000*   
LC3plus                    0.424    0.050*   0.000*   
liblc3                              0.244    0.000*   
LAMECBR1                                     0.001*   
-----------------------------------------------------------------------

AAC(Apple) is better than LC3plus, liblc3, LAMECBR128kbps, LAMECBR64kbps
AAC(FDK) is better than LC3plus, liblc3, LAMECBR128kbps, LAMECBR64kbps
LC3plus is better than LAMECBR128kbps, LAMECBR64kbps
liblc3 is better than LAMECBR64kbps
LAMECBR128kbps is better than LAMECBR64kbps

Raw data:

Code: [Select]

AAC (Apple)	AAC (FDK)	LC3plus	liblc3	LAME 128kbps	LAME 64kbps
%feature	5	Opus ⇒ AAC	Opus ⇒ AAC	Opus ⇒ LC3	Opus ⇒ LC3
%feature	7	 	 	 	 	MP3	MP3
%feature	10	CoreAudioToolbox 7.10.9.0, via qaac 2.72	FDK-AAC 2.0.2	V1.6.3 ETSI (floating point ver.)	liblc3 Apr 20, 2022	LAME 3.100.1-x64	LAME 3.100.1-x64
%feature	11	--cbr 160	-c:a libfdk_aac -b:a 160k	160000	-b 160000	-b 128	-b 64
%feature	12	from Opus 128kbps	from Opus 128kbps	from Opus 128kbps	from Opus 128kbps	from original	from original
%genre Kamedo2's 15 sample
4.300	4.400	4.100	3.700	3.200	1.800	
4.700	4.500	4.200	3.700	4.100	1.700	
4.500	4.300	3.900	4.100	4.400	1.600	
4.500	4.400	4.100	3.900	3.700	2.100	
3.800	4.100	3.500	3.600	2.500	1.700	
4.300	4.200	3.700	3.400	3.800	1.700	
4.400	4.500	4.100	3.900	2.900	2.400	
4.400	4.500	3.600	4.100	3.900	1.700	
3.900	3.800	4.300	4.400	4.100	2.700	
4.500	4.400	3.900	3.500	3.600	1.800	
4.400	4.300	4.100	4.200	3.100	1.600	
4.200	4.100	3.900	3.700	3.300	2.200	
4.400	4.500	3.800	3.700	3.600	1.700	
4.200	4.400	3.900	3.800	3.600	1.600	
4.400	4.300	3.600	3.700	4.100	1.800		
%genre IgorC's 12 sample
4.400	4.500	4.100	4.000	2.700	1.800	
4.100	4.400	4.600	4.500	3.600	1.600	
4.600	4.500	4.100	4.200	3.200	1.700	
4.300	4.400	3.900	3.800	3.600	1.900	
4.500	4.200	4.400	3.800	3.600	1.900	
4.300	4.200	3.800	3.700	3.200	2.100	
3.900	3.700	3.400	3.500	2.800	1.600	
4.100	4.400	3.900	4.300	2.600	1.900	
4.500	4.600	3.900	3.700	4.100	2.100	
4.200	4.300	3.800	3.500	4.100	2.200	
5.000	4.800	4.700	4.400	4.500	2.300	
4.700	5.000	4.400	4.300	4.100	2.200	

%samples	41_30sec	Perc.
%samples	finalfantasy	Strings
%samples	ATrain	Jazz
%samples	BigYellow	Pops
%samples	FloorEssence	Techno
%samples	macabre	Classic
%samples	mybloodrusts	Guitar
%samples	Quizas	Latin
%samples	VelvetRealm	Techno
%samples	Amefuribana	Pops
%samples	Trust	Gospel
%samples	Waiting	Rock
%samples	Experiencia	Latin
%samples	Heart to Heart	Pops
%samples	Tom's Diner	Acappella

%samples	01 castanets	inst.
%samples	02 fatboy_30sec	Techno
%samples	03 eig	Techno
%samples	04 Bachpsichord	inst.
%samples	05 Enola	Techno
%samples	06 trumpet	inst.
%samples	07 applaud	Live
%samples	08 velvet	perc.
%samples	09 Linchpin	Rock
%samples	10 spill_the_blood	guitar
%samples	11 female_speech	Speech
%samples	12 French_Ad	Speech

Bitrates:
All encoders were tested with CBR settings, therefore every tracks of AAC and LC3 is very close to 160kbps.

Code: [Select]

%bitrate
AAC (Apple)	AAC (FDK)	LC3plus	liblc3	LAME CBR 128kbps	LAME CBR 64kbps	
162387	161978	161014	161659	128285	64154
162562	162020	160979	161667	128230	64196
162879	162365	160984	161655	128372	64266
162679	162084	161015	161646	128319	64214
162749	162340	160981	161652	128368	64267
162989	162338	160987	161719	128440	64278
162974	162222	161016	161679	128458	64286
162331	162011	160989	161658	128271	64202
163932	163180	161141	161773	128827	64534
162628	162092	160980	161683	128295	64199
162327	161897	161024	161667	128244	64205
163037	162391	161182	161834	128553	64319
162736	162244	161050	161634	128353	64260
162391	162100	160983	161628	128304	64185
162832	162343	161019	161702	128470	64276
165547	163738	161116	161762	129023	64827
162311	161976	161009	161624	128336	64161
163482	162617	161070	161709	128613	64406
162476	162136	160979	161669	128396	64204
162317	162027	161015	161648	128300	64203
164590	163095	161051	161759	128666	64466
165505	163638	161164	161773	128851	64589
164116	162966	161075	161768	128639	64396
163213	162632	161036	161696	128588	64332
162477	162004	161025	161649	128264	64195
162842	162243	160988	161630	128432	64282
163657	162689	161047	161716	128663	64396

Other tests:

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #1 – 2022-06-11 21:12:48

Thanks for the test!

Extrapolating a little bit, LC3 looks to be similar in audio quality to MP3, possibly worse. It might need 200+ kbps for high quality. (And a stable 200+ kbps Bluetooth connection is not guaranteed even when just moving around the room, IME.)
It didn't do great on the few vocal/speech samples, either.
I hope that at least it has really low latency.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #2 – 2022-06-12 04:24:59

fix: LC3, the tested version of google / liblc3 is 67dcc7c, Apr 19, 2022.
6 commits on Apr 20, 2022 were not reflected in the tested binary.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #3 – 2022-06-12 11:59:26

Great test Kamedo.
I appreciate all the hard work you are putting into these tests.

I have one question for you. What is your preferred encoder for AAC-LC at around 144 or 160 kbit/s?
(From lossless sources. No re-encoding.)

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #4 – 2022-06-12 13:44:45

Quote from: Markuza97 on 2022-06-12 11:59:26

What is your preferred encoder for AAC-LC at around 144 or 160 kbit/s?

The Apple's CoreAudio engine. You can use it via qaac on Windows, and afconvert on Mac. This engine is mature and very stable.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #5 – 2022-06-14 06:31:23

Very interesting, it looks like CoreAudio is no longer the definitively superior AAC encoder. I believe it hasn't been updated since 2010, so FDK-AAC (which is Android's AAC encoder, is it not?) has had plenty of time to catch up.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #6 – 2022-06-14 10:33:38

No "quality" difference.
There is two ways of development:
1. refresh patent license.
2. avoid patent royalty.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #7 – 2022-06-17 16:13:21

Quote from: whitepuzzle on 2022-06-14 06:31:23

Very interesting, it looks like CoreAudio is no longer the definitively superior AAC encoder.

This was a Bluetooth codec test, so CoreAudio was forced to be CBR, while FDK-AAC is CBR on default.
Probably CoreAudio will be even closer to original on CVBR. That's the setting CoreAudio has been extensively used and tested.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #8 – 2022-06-17 16:51:32

I'd ask why this was being done on a PSP? A really nice headphone amp and DAC are only £100. Do you have measurements for the headphone amp and DAC in the PSP?

This seems like a huge oversight to me. All it says is that when I pay x on a PSP, I can't tell the difference.

Will HA ever understand the rest of the chain is important?

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #9 – 2022-06-18 02:24:02

Quote from: NateHigs on 2022-06-17 16:51:32

I'd ask why this was being done on a PSP? A really nice headphone amp and DAC are only £100. Do you have measurements for the headphone amp and DAC in the PSP?

This seems like a huge oversight to me. All it says is that when I pay x on a PSP, I can't tell the difference.

Will HA ever understand the rest of the chain is important?

I wondered the same thing, considering how old the PSP is, but that doesn't make me doubt the results. If the DAC is so important, feel free to provide ABX results demonstrating that you can hear a difference between different DACs when all other factors are equal. The PSP isn't nearly old enough to be from the era when D2A and A2D conversions were dicey. The burden of proof lies with anyone who claims the PSP's DAC is lacking.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #10 – 2022-06-18 10:53:24

Here there are significant differences on equal hardware, so the playback chain is good enough for those to be clear.
There is no plausible reason that cheap hardware should create differences.

Had the results been no difference consistently, it could have been due to one or a combination of more of the following
codecs being equally good to most users
codecs being indistinguishable to this particular user who doesn't have the best ears
playback chain being so bad that it erases all audible differences
... and one would have wished for some other user on some other hardware to try to replicate the study, right?

(Which of course isn't a bad thing in any case - replication, I mean.)

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #11 – 2022-06-18 11:42:37

At 100-200kbps these codecs only have no more than 30dB of SNR, except for simple synthetic signals like sine waves and such, DAC quality is irrelevant here. Poor combination of headphone and amp could be an issue though, if someone delibrately wants to do so.

https://hydrogenaud.io/index.php?topic=39970.0
For the record I was able to ABX 320CBR mp3 with LAME 3.96.1 and 3.97b2 and the sample used was not considered as a killer sample by other members, and that test was done on an $128 sound blaster and $25 Sony earbud (not even IEM) in 2005.
[EDIT] The audio sample in the link above is dead, for those who want to try, download the attached flac.
[EDIT2] Strange. "Your file is too large. The maximum attachment size allowed is 0 KB." Can @Peter or @spoon help?

Lossy codecs are based on exploiting psychoacoustics, not about typical "SINAD" and such. This article should be a good starting point:
https://izotope-rx.livejournal.com/5760.html

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #12 – 2022-06-18 13:45:00

Quote from: bennetng on 2022-06-18 11:42:37

At 100-200kbps these codecs only have no more than 30dB of SNR, except for simple synthetic signals like sine waves and such, DAC quality is irrelevant here.

Are the SNR ratio and THD percentage figures that informative on good codecs? After all, those are developed to make the "N" and the "D" less annoying, rather than good looking.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #13 – 2022-06-18 14:08:01

Quote from: Porcus on 2022-06-18 13:45:00

Are the SNR ratio and THD percentage figures that informative on good codecs? After all, those are developed to make the "N" and the "D" less annoying, rather than good looking.

My observation on several codecs is that opus often has poorest performance on simple tones. Sometimes can be improved by changing framesize as mentioned here:
https://hydrogenaud.io/index.php/topic,122093.msg1007920.html#msg1007920

LAME for example, when using the older versions with some debug switches, can be forced to use only long blocks to optimize tonal performance. A very detailed thread, in a sarcastic way:
https://hydrogenaud.io/index.php?topic=4457.0

Of course, measuring tonal performance alone is deceiving and many long time HA members know about these things very well. Things like pre-echo and stereo separation cannot be ignored too.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #14 – 2022-06-18 16:48:11

Interesting, thank you for the test!
Do we know for sure 160kbps is a representative bitrate to test LC3 in future Bluetooth LE Audio scenarios? I'm only asking because the codec it replaces (SBC) is typically running at 328kbps. Halving the bitrate makes sense, but I haven't seen any document about this yet.

Mod: I've found this chart. This does include 160kbps, but at the low end. Wonder what will be the typical bitrate.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #15 – 2022-06-23 14:22:08

It looks like 160kbps is too low for the production quality. (3.89 for liblc3)

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #16 – 2022-08-14 07:23:10

It has been a few years since I looked into it but I *think* there are a few nit-picks with this test.

1. Opus 128kbps being the Source. I think 256Kbps AAC or Opus would have been a better representation. Or straight up using lossless as original. Unless you are using the Web version on a free tier, subscription Music or even YouTube offers 256Kbps AAC files if not higher.

2. Most bluetooth earphones dont do AAC pass through, contrary to popular believe despite the devices itself support AAC like the Apple AirPod. i.e If you are listening an AAC files it will still get (Hardware) re-encoded if you are listening on AirPod. I am assuming LC3 will have mandatory pass through on BT 5.2. But I never had time to check on it. That means testing AAC software encoder against LC3 wouldn't be an accurate use cases, especially with CoreAudio.

3. Would have been nice if the test was on LC3 256kbps, which is sort of the sweet spot for this codec. And again contrary to popular belief having a consistent low latency 256kbps connection in modern bluetooth isn't unattainable.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #17 – 2022-08-14 09:19:25

Quote from: iwod on 2022-08-14 07:23:10

1. Opus 128kbps being the Source. I think 256Kbps AAC or Opus would have been a better representation. Or straight up using lossless as original. Unless you are using the Web version on a free tier, subscription Music or even YouTube offers 256Kbps AAC files if not higher.

I kinda agree. I think using a lossless source would make the most sense.

Quote from: iwod on 2022-08-14 07:23:10

I am assuming LC3 will have mandatory pass through on BT 5.2.

What makes you think so? Passing through a lossy stream directly is a significant technical and usability challenge, mainly because you can't mix OS sounds (you'd need parallel streams...). I doubt it's going to be a thing outside of hacky 3rd party implementations. The target audience for this feature is just too small.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #18 – 2022-09-13 07:04:04

Quote from: iwod on 2022-08-14 07:23:10

1. Opus 128kbps being the Source. I think 256Kbps AAC or Opus would have been a better representation. Or straight up using lossless as original. Unless you are using the Web version on a free tier, subscription Music or even YouTube offers 256Kbps AAC files if not higher.

I agree, in that the choice should've been between 256 kbps AAC or Lossless.
Most people stream these days, so a practical usecase would be reflected by the former choice.
However, if the goal is to simply compare state of consumer wireless tech from an experiential perspective, the latter is ideal.

Either way, Opus 128kbps only reflects the incredibly tiny sliver of users who might download music in FLAC, encode it to Opus@128 AND own a wireless pair of headphones.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #19 – 2022-09-13 07:18:34

Quote from: Razor54672 on 2022-09-13 07:04:04

Quote from: iwod on 2022-08-14 07:23:10
1. Opus 128kbps being the Source. I think 256Kbps AAC or Opus would have been a better representation. Or straight up using lossless as original. Unless you are using the Web version on a free tier, subscription Music or even YouTube offers 256Kbps AAC files if not higher.
I agree, in that the choice should've been between 256 kbps AAC or Lossless.
Most people stream these days, so a practical usecase would be reflected by the former choice.
However, if the goal is to simply compare state of consumer wireless tech from an experiential perspective, the latter is ideal.

Either way, Opus 128kbps only reflects the incredibly tiny sliver of users who might download music in FLAC, encode it to Opus@128 AND own a wireless pair of headphones.

So users of YouTube are an incredibly tiny sliver?

I think the reasoning here is sound: Spotify uses Vorbis, Youtube uses Opus. AAC is a codec being tested, so it makes sense not to use that. Streaming lossless is not affordable for a lot of people.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #20 – 2022-12-03 17:48:09

Quote from: ktf on 2022-09-13 07:18:34

AAC is a codec being tested, so it makes sense not to use that.

That's not a good reason to ignore it. It's going to be used, a lot. And it's also not obvious/guaranteed that generational loss within the same codec has a huge advantage, especially so when encoder flavors are different.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #21 – 2023-01-26 12:07:33

Hello. My name is Alexander from Fraunhofer IIS.

Thx to Kamedo2 for doing this extensive listening evaluation and sharing it in this forum. It looks reasonable that in this test setup, AAC-LC performs better than LC3. However, there are a few things to consider.

Bitrate:
LC3 was specifically developed for isochronous transport channels within Bluetooth LE Audio. For TWS ear buds (and likely for any other audio device), each audio channel is transmitted via individual transport channels. AAC-LC uses joint stereo coding which means that the payload sent to each device contains both channels (e.g., 160 kbps) while with LC3 just the corresponding channel (80 kbps) is sent to each ear-piece. At this point the Low Energy factor kicks in as energy consumption is mainly related to the payload size sent over the air. Even if LC3 is using a higher bitrate (e.g., 96 kbps or 124 kbps per channel), the payload size sent through the air is lower compared to AAC-LC (160 kbps per channel).

Delay:
AAC-LC has a delay of 59.5 ms while LC3 works with a delay of 13.6 ms at 44.1 kHz. Rule of thumb: Reducing delay by factor 2 requires 25% higher data rate!
Alternatively, one could use AAC-ELD as reference point which offers a delay of 16.3 ms at 44.1 kHz at a similar bitrate as LC3.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #22 – 2023-01-26 12:09:32

Quote from: Kamedo2 on 2022-06-23 14:22:08

It looks like 160kbps is too low for the production quality. (3.89 for liblc3)

The 80 kbps per channel (160 kbps stereo) setting of LC3 is the minimum required bitrate for music streaming. Ideally, 96 kbps or 124 kbps per channel are used (as standardized in the Bluetooth LE Audio Telephony and Media Audio profile). Higher bitrates show significant improvement (see BS.1116 Bluetooth results https://www.bluetooth.com/blog/a-technical-overview-of-lc3/).

Bitrates lower than 80 kbps per channel are not standardized for music streaming with LC3 in Bluetooth. Note that the bitrate used in a similar listening test LC3 vs. AAC at 48 kHz 144 kbps (72 kbps per channel for LC3) performed by Kamedo2 is not standardized/allowed in Bluetooth.

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #23 – 2023-01-26 12:11:43

Quote from: Porcus on 2022-06-18 13:45:00

Quote from: bennetng on 2022-06-18 11:42:37
At 100-200kbps these codecs only have no more than 30dB of SNR, except for simple synthetic signals like sine waves and such, DAC quality is irrelevant here.

Are the SNR ratio and THD percentage figures that informative on good codecs? After all, those are developed to make the "N" and the "D" less annoying, rather than good looking.

Even though SNR/THD+N measurements may not be representative for the perceptual quality of the audio codecs, they provide reliable information on how accurate a codec can reproduce the signal.
When a codec is used in a closed system, it’s important that the codec is not the weakest element next to amplifiers, converters etc. – here the THD+N metric can indeed be helpful to evaluate that.

The sibling of LC3 is LC3plus which has a dedicated support for High-Res audio and performs excellent in terms of SNR and THD+N.
For THD+N figures of LC3plus, we would like to point to page 9 of the technical paper https://secure.aes.org/forum/pubs/conventions/?elib=21084 .

Re: Personal blind comparison of the Bluetooth codecs, AAC vs LC3, re-encoding

Reply #24 – 2023-01-26 13:28:35

Hello, and thanks to HolyMusic for the detailed analysis.

Quote from: HolyMusic on 2023-01-26 12:07:33

For TWS ear buds (and likely for any other audio device), each audio channel is transmitted via individual transport channels. AAC-LC uses joint stereo coding which means that the payload sent to each device contains both channels (e.g., 160 kbps) while with LC3 just the corresponding channel (80 kbps) is sent to each ear-piece. At this point the Low Energy factor kicks in as energy consumption is mainly related to the payload size sent over the air. Even if LC3 is using a higher bitrate (e.g., 96 kbps or 124 kbps per channel), the payload size sent through the air is lower compared to AAC-LC (160 kbps per channel).

Good point. What I have done is to select settings so that the bitrate, in a classical file-based sense, will be equal; not the payload size sent over the air, according to the each Bluetooth protocol.

The following argument assumes True Wireless Stereo (TWS).

With Bluetooth Classic Audio, both channels have to be sent over the air to the left earbud first, and then, the left earbud have to carry the burden of having to transmit the entire payload over the air to the right earbud. Joint stereo coding means there is no easy way to avoid having to carry the left-side contents to the right earbud.

With Bluetooth LE Audio, the smartphone only needs to send the left sound to the left earbud and the right sound to the right earbud, easy, which is just fine because LC3 use simple stereo when the bit rate is 128k or more.

So, in this particular setting tested in this listening test, the total payload will be smaller in LC3.

Notice