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Is LDAC lossy or bit-perfect for 44.1kHz/16bit (Red Book CD) files?

przemnet

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Hi,

In theory, SONY claims that file 44.1kHz/16bit (Red Book CD) sent over Bluetooth with LDAC (*when used speed is 990kbps) should be the same as original file and sending Hi-Res files like 96kHz/24bit is lossy.

ldac.png



However:

1/ WAV file 44.1kHz/16bit has bitrate about 1400kbps (16*44100*2=1411200). Typically FLAC compression decreases the file size to 50 and 70 percent of its original size so the bitrate would be 750-950kbps so less than 990kbps which is OK. However, what about some rare files with compression ratio of 80 percent and higher? Their bit rate is more than 990kbps- what happens in that case?


2/ In this article https://www.soundguys.com/ldac-ultimate-bluetooth-guide-20026/ it is written:
"it’s quite unlikely that your phone will opt for 990kbps LDAC unless you manually force the settings via the developer options."

I checked my phone and by default "Bluetooth audio LDAC codec" is set to "Best effect (Adaptive bit rate)" and I have to change it manually every time when I connct to a DAC to "Optimized for audio quality (990kbps/909kbps)" which is quite annoying.

Second thing is that by default, when I connect to the DAC, "Bluetooth Audio Sample Rate" is set to 96kHz and "Bluetooth Audio Bits Per Sample" is set to 32bit.
What happens in that case when I'm streaming 44.1kHz/16bit content?
Is it upsampled to 96kHz/24bit and lossy sent to the device?
Do I have to manually change "Bluetooth Audio Sample Rate" to 44.1kHz and "Bluetooth Audio Bits Per Sample" to 16bit when I want to stream losselessly 44.1kHz/16bit files?


For me the question is, whether sending 44.1kHz/16bit (Red Book CD) file over Bluetooth with LDAC is really bit-perfect?

If yes, this would be enough for me since I could loselessly stream TIDAL HIFI content. However I have some doubts as mentioned above...

Can anyone answer this ?

Cheers,
Przemek
 

Jmudrick

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I'm guessing phones are different. In Developer Options my LG v30+ allows me to fix LDAC at 16/44.1 if I want.
 
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przemnet

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I'm guessing phones are different. In Developer Options my LG v30+ allows me to fix LDAC at 16/44.1 if I want.
Yes, that is exactly the same as in my case as described in initial post and I believe it is similar in most of Android phones when you unlock Developer Settings ;-)

This is not very convenient to change those settings every time I connect to the DAC, however I could live with that provided that transmission with below settings in Developer Options is really bit-perfect:

Bluetooth audio LDAC codec: Optimized for audio quality (990kbps/909kbps)
Bluetooth Audio Sample Rate: 44.1kHz
Bluetooth Audio Bits Per Sample: 16bit

Is it?

Looking forward,
Przemek
 
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przemnet

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LDAC has a maximum bit rate lower than uncompressed CD quality, so it is necessarily lossy. It is likely to incur very little loss for most music content, but it won't be bit-perfect.
I agree, as I wrote initially, WAV file 44.1kHz/16bit has bitrate about 1400kbps (16*44100*2=1411200). Typically FLAC compression decreases the file size to 50 and 70 percent of its original size so the bitrate would be 750-950kbps so less than 990kbps. However there might be problem with some rare files with compression ratio of 80 percent and higher.

But maybe SONY developed compression which is smarter than FLAC and they are able to always compress CD quality files to a bitrate lower than 990kbs?

Anyone can confirm / deny it ;-)?

Cheers,
Przemek
 
Last edited:

Asylum Seeker

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Whether you have to go into developer options or you can select on the BT menu is a matter of phone user interface. On Samsung you have to go into developer options. On Huawei and Xiaomi UI, you don't.
 

scott wurcer

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That is mathematically impossible.

Lossless compression has a hard limit at the Shannon entropy, I doubt any of the popular algorithms get right up to exactly the limit so there is some variance in performance. It's a matter of probability, a music file that could only be reduced to 80% would be fantastically improbable.
 

chasfs

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This is an interesting discussion. First I would encourage you to try the different LDAC settings and see if you notice a difference. See if you notice a difference between LDAC adaptive and LDAC 990. Or between LDAC adaptive and APTX-HD.

Bit for bit perfection is a fine goal but most double blind studies show that no one can tell the difference once you get above 300kbps
 

JSHamlet234

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Looking over my collection, I have quite a few 16/44 FLAC files that are over 990Kbps.

3 Doors Down "The Better Life":

Duck and Run: 1050Kbps
Better Life: 1032Kbps
Down Poison: 1015Kbps
Smack: 1067Kbps
So I Need You: 1000Kbps

That's 5 on just one album.

Out of curiosity I tried to 7Zip them to see if stacking another random lossless algorithm could get them any smaller, but the compressed size was 99.9984% of the original.
 

Tks

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I wouldn't worry much. The only time this wouod be an issue from a consumer standpoint was if you could blind test the differences without much effort. Otherwise just enjoy the benefits of wireless freedom.
 

mansr

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Lossless compression has a hard limit at the Shannon entropy, I doubt any of the popular algorithms get right up to exactly the limit so there is some variance in performance. It's a matter of probability, a music file that could only be reduced to 80% would be fantastically improbable.
For any lossless compression algorithm there must exist inputs that it can't compress. With an input N bits long, there are 2^N different possibilities. If the output is M bits, there are 2^M possible combinations. If M < N there are thus fewer possible outputs than inputs, which means it can't be lossless. In fact, if a lossless algorithm can compress some inputs, it must necessarily increase the size of some others.

Regarding probabilities, it is of course unlikely that an entire song is incompressible. However, short sections of a song may be noise-like and thus difficult to compress. Such a section could thus cause the instantaneous bit rate to exceed the limits of a communication link.
 

scott wurcer

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However, short sections of a song may be noise-like and thus difficult to compress. Such a section could thus cause the instantaneous bit rate to exceed the limits of a communication link.

A mis-understanding, I was only considering off line lossless compression. The algorithms vary by compute load and how close to the theoretical limit they get but lossless is lossless.
 

maverickronin

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I found a 16/44 FLAC file in my collection at 1318kbps. :eek:
 

scott wurcer

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I found a 16/44 FLAC file in my collection at 1318kbps. :eek:

What settings? Just curious because some of the numbers here don't jive with published benchmarks. https://xiph.org/flac/comparison.pdf
An only 7% reduction would represent almost two independent channels of uncorrelated noise.

With respect to loss vs. file size I use the minimum size determined by the entropy of the data, of course this is different for each file. The encode half of all the codecs vary in how close they get to this limit.
 

maverickronin

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What settings? Just curious because some of the numbers here don't jive with published benchmarks. https://xiph.org/flac/comparison.pdf
An only 7% reduction would represent almost two independent channels of uncorrelated noise.

I didn't do the encoding myself as it was downloaded from Bandcamp. I can't seem to make it any smaller with dBpoweramp's FLAC plugin though. The metadata says it was encoded with reference libFLAC 1.2.1 20070917. Transcoding to wav and compressing with 7zip (LMZA ultra, single thread) only gets down to 85%

I have some weird stuff though, and this is definitely a killer sample. It actually is full of uncorrelated noise. (Turn your volume down.)
 
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