While the audio chip inside a smartphone has always been the main marker of its audio performance, in actuality it is just part of the whole equation. Great audio quality from a phone comes from a multitude of factors like:
1) Audio chips (DAC, I/V converters & headphone amplifiers)
2) Power Supply
3) Overall audio topology/ circuit design used inside the phone
4) Shielding used for less analog signal interference
For any audio chip to provide maximum performance, it requires un-adulterated power (in watts) straight from the battery. This is where high quality power supplies becomes very important which does this specific job. These power-supply circuits have dedicated paths to draw power straight from the battery. Power is then conditioned & filtered using high quality audio capacitors to provide power to the audio chips. Provide stable maximum power to any audio chip will yield maximum performance from the chip. Next are the audio chips, like DACs which may require ancillary components like oscillators which need to provide correct information to DACs. Using a symmetrical audio circuit topology with high quality of components in the entire audio chain is most important. Remember the audio is as good as the weakest link in the chain. So using high quality audio capacitors, resistors in the circuit is very important. Finally, the generated audio signal emanated from the inbuilt DAC and passed through the converters & op-amps to the audio jack needs to be properly shielded from the digital circuits in the phone. If not done properly it can induce noise to the final audio signal. If all these criteria's are taken proper-care of, chances are you have a great audio centric smartphone.
Taking LG out of the equation, I can only think of Vivo & Meizu as the only two manufactures who are producing audio centric phones to-date. I will only be speaking of phones which are readily available.
Vivo divides its audio implementation into:
a)
HiFi 2.0 Architecture (Best): This circuit design takes care of the all four factors mentioned above.
1) Vivo NEX S: Cirrus Logic CS43199 (DAC) + (3 X Analog Devices SSM6322)
2) Vivo X50 Pro Plus: Cirrus Logic CS43131
3) IQOO 5 Pro: Cirrus Logic CS43131 (IQOO sub-brand of Vivo)
b)
HiFi 1.0 Architecture (Great): This takes of some factors mentioned above.
1) Vivo X50 Pro: AKM AK4377A
2) Vivo NEX 3/3S: AKM AK4377A
3) IQOO 3: AKM AK4377A
As far as I know, Samsung and Oppo uses flagship Qualcomm audio chips for their flagship devices. I own Meizu's last flagship with a headphone jack, the Meizu 16th on 2018. After that model they went the Apple way and omitted the audio jack. You now have to pay extra cash to get a digital audio dongle from them to listen audio from their latest flagship Meizu 17/ 17 Pro. However the dongles are very good using Cirrus Logic CS43131 internally.
Meizu 16th to me is an example of audio done right on a smartphone. It uses the unknown flagship Aqustic WCD9341 audio chip from Qualcomm and sounds great. Spec-wise the WCD9341 is right there with AKM AK4377A, so Meizu being a manufacturer from audio background did the basics right. Provided the WCD9341 with all the power it needs to perform in its high performance mode (other manufacturers seldom do this as it requires more money to be spent in power supply circuit). Made a good circuit design to implement the WCD9341 and finally provided dedicated metal shielding to the chip and its circuits. Voila, now have a Meizu 16th using an unknown WCD9341 audio chip right there with my Vivo X21UD with AKM AK4376A!!!
Similarly, the audio chip is same for both Vivo X50 Pro Plus & IQOO 5 Pro but the performance is different. IQOO took the same design from X50 Pro Plus but compromised on the power supply to save money. Hence the headphone output gain is much higher on Vivo than IQOO. On naked eye it will be assumed both have same performance as both uses the same audio chip. As I say, the devil is in the details.