[mcnaugha]

I may have a bigger problem which I am trying to investigate. The ROG Phone 8 just shows 24-bit for the PCM Bit Depth. There is no option to switch the codec to 16-bit. I am contacting support but I don't hold out much hope of a good answer. I don't know where to check in their AOSP source code for where they could have hardcoded 24-bit only. So, it's hard to tell if we still get actual aptX Lossless with this current OS. We need an Android extension which shows the live BT bit rate at the top of the screen or something like that. It's the only way you can know, when you see a 1Mbps or higher bit rate. I think it is so sensitive and variable that they decided not to provide a default visual way to tell if you're enjoying lossless. The developer of Bluetooth Codec Changer might be our best hope for improved lossless monitoring in the future.

In a follow-up to the above... I just spent a week trying to find a way to confirm I was getting aptX Lossless. Turns out you literally need Qualcomm’s diagnostic software (QXDM) or to capture the packets arriving at the receiver and confirm they contain lossless data.

I mentioned the Android log entries previously which may be giving away that the codec is primed for lossless, with the key one being:

aptxalsCodecConfig: SetAudioProfileHighQuality AUDIO_PROFILE_16_BIT_SOURCE

This is a log entry from aptX ALS, which is an Android service/agent supplied by Qualcomm that watches what's going on with audio in your Android device and adapts the codec configuration as necessary. It monitors what audio apps you're using and what the specification is of the audio playing back.

For the moment, I am assuming the codec only operates configured in 24-bit mode and that it uses this to transmit the 16-bit lossless data encapsulated within. The data packets have a unique configuration or flag which allows the decoder to know they’re lossless.

Also I found that it was not reliable in reconfiguring the codec to 44.1kHz. On some occasion, it would simply stay in 96kHz mode. This aligns with the note @ImMaleven got from Flairmesh, talking about it favouring 96kHz. A workaround to this is to use Bluetooth Codec Changer’s adaptive sample rate changer (which is a beta feature btw). This does interrupt playback during a sample rate change but always ensures the codec is in 44.1kHz mode when playing 16/44.1. I saw proof of this in my testing and comparing the log entries.

The dev of Bluetooth Codec Changer advised that he doesn’t have devices with aptX Lossless and therefore can’t do anything special to help in his app yet. He confirmed you'd need root access to be able to display the realtime/live Bluetooth bit rate. So, probably only something an OEM could build in to their Android build or you'd need a rooted build. Seeing the live bit rate is possibly the only way we could ever know that our devices were doing the lossless thing.


Roll-on XPAN is what I say. All of this complexity will hopefully go away... although knowing Qualcomm, that might just be wishful thinking.

 

[mcnaugha]

Somewhat off topic but since you know about bluetooth, I've been researching how to retrofit a Woojer vest for low latency audio. The low latency codecs all strip out the low end, I was hoping LHDC was better. But I'm not sure there's any LHDC receiver that works aside from the Ifi zen series. Is there an analog solution or any ideas on that? I tried a cheapo wireless guitar system from amazon and it sounds like old fm radio.

I've never pursued low latency myself. Just been pursuing high quality audio without giving latency a second thought. So, I'm not sure I can help.

You tried aptX Adaptive in LL/gaming mode and it sounded bad too?


You might need to wait and see what XPAN brings to the table. There seems to be an implication that audio over Wi-Fi delivers both lossless and low latency but I don't have any documentation on it yet.


This also reminds me that FiiO is working on a new "transmitter decoder" labelled the BTA50. It's not pencilled-in to appear until Autumn/Fall. A month ago, they invited suggestions for the product, before it is finalised. Maybe they'll add LHDC as they have been trying to revive this codec.

I did think though that there was a special separate low latency codec by the same people. LLAC. I don't know if it is standalone or if it's rolled into LHDC.

 

[LosslessLover]

Finally got an aptx lossless transmitter FMA120

I sent an email to Flairmesh and they immediately went and updated the device firmware to support AptX Lossless. I'm the only person to review on Amazon, so I'm probably the first person to ask for this. I had it on 96khz for Aptx adaptive and it cut out. I read somewhere that the bluetooth codec doesn't downsample anything, you have to use the correct mode. The instability and cutting out I had on 96khz seems to work fine now.

Wow, it finally happened, just bought the last one on amazon! Also super proud that the first aptX lossless dongle was designed in Australia.

 

[ImMaleven]

I've never pursued low latency myself. Just been pursuing high quality audio without giving latency a second thought. So, I'm not sure I can help.

You tried aptX Adaptive in LL/gaming mode and it sounded bad too?


You might need to wait and see what XPAN brings to the table. There seems to be an implication that audio over Wi-Fi delivers both lossless and low latency but I don't have any documentation on it yet.


This also reminds me that FiiO is working on a new "transmitter decoder" labelled the BTA50. It's not pencilled-in to appear until Autumn/Fall. A month ago, they invited suggestions for the product, before it is finalised. Maybe they'll add LHDC as they have been trying to revive this codec.

I did think though that there was a special separate low latency codec by the same people. LLAC. I don't know if it is standalone or if it's rolled into LHDC.

As far as I can tell LLAC is just the reverse of the aptx Lossless on LHDC, but segmented to at least LHDC V3+. All of this is from 2018 or 2019 I think. The new LHDC one has it, and the documentation only suggests the dongle itself supports V3 and up. Would be nice if they answered emails about it, but they don't. Good to know about XPAN though thanks.

 

[O11111]

As far as I can tell LLAC is just the reverse of the aptx Lossless on LHDC, but segmented to at least LHDC V3+

There are several LHDC versions. 1 and 2 are very rare these days and not that interesting. 3 is a modification of 2 with LPC, 4 is almost the same as 3 and LLAC ("Low Latency Audio Codec") is basically LC3plus. In fact, both 4 and LLAC are just flags for 3. Generally, most recent devices have both 4 and LLAC flags and select one of them based on the sample and bit rates.
5 is different from all the previous versions and consists of 2 "subcodecs": lossy and lossless. Lossy is MDCT + SNS (up to 192 kHz/24 bits), lossless is LPC (up to 96/24, but seems to only be available on Airoha/Mediatek MHDT whatever it is), both are then arithmetically encoded.

 

[ImMaleven]

There are several LHDC versions. 1 and 2 are very rare these days and not that interesting. 3 is a modification of 2 with LPC, 4 is almost the same as 3 and LLAC ("Low Latency Audio Codec") is basically LC3plus. In fact, both 4 and LLAC are just flags for 3. Generally, most recent devices have both 4 and LLAC flags and select one of them based on the sample and bit rates.
5 is different from all the previous versions and consists of 2 "subcodecs": lossy and lossless. Lossy is MDCT + SNS (up to 192 kHz/24 bits), lossless is LPC (up to 96/24, but seems to only be available on Airoha/Mediatek MHDT whatever it is), both are then arithmetically encoded.

Lol...I did a bit of research and I came up with almost nothing on LHDC. Did you get all this from the source code? Wish they would publish even a fraction of what Qualcomm publishes. I even tried github and it seemed like they never updated or posted code for the LHDC project they started on there. Any idea on how to make an LLAC receiver setup work? I looked into the FIIO BTR3 and Shanling up4 22 and they don't work obviously. Would like to make this work and not return the LHDC one. The iFi zen looks like maybe it might be what I need...but they're all powered by 5v or the battery powered one is $200.

 

[O11111]

Did you get all this from the source code?

There's not much info in the source code, because LHDC is a proprietary codec and there's no publicly available source code. Well, not for me. I'm working on an open-source implementation.

Any idea on how to make an LLAC receiver setup work?

If supported, it should automatically work if you select 48 kHz and bitrate is adaptive or < 500 kbps. Which receiver do you want to make it work with?
BTR3 just doesn't support LLAC. UP4 also probably doesn't (based on aptX LL claim, it must be using some old Qualcomm chip).

 

[cattboy]

. I'm working on an open-source implementation.

Go on... github when

 

[ImMaleven]

There's not much info in the source code, because LHDC is a proprietary codec and there's no publicly available source code. Well, not for me. I'm working on an open-source implementation.

If supported, it should automatically work if you select 48 kHz and bitrate is adaptive or < 500 kbps. Which receiver do you want to make it work with?
BTR3 just doesn't support LLAC. UP4 also probably doesn't (based on aptX LL claim, it must be using some old Qualcomm chip).

Well I wanted to know if you could confirm there's any receiver that works. I mean I can get earbuds, but the LHDC ONE doesn't do anything for me if I can't have a universal 3.5mm type of receiver. I didn't really understand this comment when I first wrote it though. Any place where we can read about the open source implementation of LHDC or how that's supposed to work?

 

[O11111]

Go on... github when

When it's ready. I'm currently working on LHDC 5 encoder.

how that's supposed to work?

LHDC will be available in many Linux distributions just like LDAC does already and probably also in Windows.

Well I wanted to know if you could confirm there's any receiver that works

Doubt that. Well, technically you'll be able to use Raspberry Pi + HiFiBerry DAC for that.

 

[ImMaleven]

When it's ready. I'm currently working on LHDC 5 encoder.

LHDC will be available in many Linux distributions just like LDAC does already and probably also in Windows.

Doubt that. Well, technically you'll be able to use Raspberry Pi + HiFiBerry DAC for that.

Yes using my own board was the next idea I had. You mean with the open source codec you're making? Might be a dumb question but will this have comparable latency to commercial LLAC products like earbuds

 

[O11111]

You mean with the open source codec you're making?

Yes.

Might be a dumb question but will this have comparable latency to commercial LLAC products like earbuds

I never tested that, so no idea.

 

[Drexxx]

Is Snapdragon Sound even necessary for driving the qc5181 chip to its fullest?
The Nura transmitter is out of stock everywhere and doesnt look like its gonna be restocked since it was bought by Denon.
The only other SS enabled transmitter if found on aptx website is the iFi audio NEO iDSD 2 but thats 800$ so its a pass.
Do you know any other SS enabled transmitter?

 

[ImMaleven]

Is Snapdragon Sound even necessary for driving the qc5181 chip to its fullest?
The Nura transmitter is out of stock everywhere and doesnt look like its gonna be restocked since it was bought by Denon.
The only other SS enabled transmitter if found on aptx website is the iFi audio NEO iDSD 2 but thats 800$ so its a pass.
Do you know any other SS enabled transmitter?

Thought this was interesting, but I'm not sure that there's anything inside of "Snapdragon Sound" that you can get on a dongle. I see it has the certification, but the actual specific features it advertises are not exclusive to this dongle. The Denon website specifically emphasizes the lossless sound, which I'm using right now on an FMA120. The spatial sound is onboard the device itself, and gaming mode refers to something I have in the FMA120 manual. This Sennheiser MTW4 advertises it(20ms) and it refers to a combination of A2DP and HFP running at the same time, according to the vendor.

https://www.aptx.com/products/nura-bluetooth-5-3-audio-transmitter

https://www.qualcomm.com/products/features/snapdragon-sound

 

[helmutcheese]

The Nuru is not Lossless as they fell back on that promise or just worded it badly AFAIR so its no better than any other Dongle like the Creative BT-W5 you get aptX Adaptive up to 24/96 in HQ and LL Modes.