[Xperia Z5 Premium Q&A, Help & Troubleshooting] _delice_doluca_:
Audio quality is noticeably low but clear. I have never tried increasing the volume with a module or playing with the mixer xml. But I know at this time, almost every phone is better at sound than this one. You can check out new LG's especially, you may find the sound quality tests at gsmarena.

BTW, I will paste what I have written in Z5 forums:

"As a previous Z2, currently Z5 Premium and also many Sony accessories owner, my humble advise is: don't buy Sony.

Not that they are bad phones in any way, however as a company, Sony can not catch up with the competition and doesn't listen to the customers.

A couple of examples:

1) DRM thing. If you happen to root your phone they say it is out of warranty and some "special" code which improves camera, screen and sound quality is lost, forever! Sure there are workarounds for these DRM keys but this doesn't chance the fact that Sony is not being developer friendly here. Also, remember the guy who sued Apple and won? The court has decided that "the software which was bought with the hardware, is fully belonged to the customer and the customer is free to customize it". So, Sony dictating us NOT to root or live without an important-ish code, which I pay for when buying the phone, is nothing but only being disrespectful to the customer.

2) camera problem. As you probably noticed, Sony phones have the highest Megapixel cameras out there. We'll, that's just a gimmick. Every Sony phone's superior auto mode shoots at 8mp. Sony also suggests that we should use 8mp whether it's superior auto or - so called- manual shooting. As a camera manufacturer, Sony sells cameras to other companies and most of them flat out come with 16mp, without any advise for a lower resolution shooting. The reason to that is, if you compare a 23mp manual shot with an 8mp manual shot at mid or low light conditions, you'll notice that there is almost no difference. Only that, the 23mp shot is bigger in size and can be zoomed more, which gives you noting but a pastel noise. In addition to that, Sony never shares its true driver for camera, rendering 3rd party camera apps almost useless as they can only register 8mp wide screen and 3.15mp 4:3 shooting mode.

Sony will never admit the truth, but my educated guess is, the sensor has to share some resources while recording the light and colors, thus making it technically save it in 23mp but physically capable of intaking enough light and real life data only for a highest quality 8mp shot. This is why 23mp clear sky shot in the morning will be good quality but a low light shot will suffer and be even lower quality than 16mp cameras. At 8mp level, it is unrivaled though.

Again, that leaves us, customers in a fooled point. Technically Sony is not lying, but also not delivering what is expected. Nowadays, Sony's only advantage to a 12-13mp Pixel or iPhone 7+ is a wide angle FOV. nothing else.

3) screen thing. We, Z5 Premium owners have an 4K screen who runs at 1080p due to the heating and battery concerns. It only converts to true 4K with supported Sony apps. Rivals switched to the 1440p already. Full time 1440p. Japanese people try to understand market's demands so rookiely here, they simply think offering a potentially higher resolution screen will attract the customers. But again, this puts them into a lower moral position than even Apple's. Look at Oneplus, they do their best for a budget screen and make it 1080p, the premium rivals like Google and LG make theirs' 1440p and Android fully supports it. Sony is already a great screen manufacturer, why try gimmicks like that? I mean with their already present screen quality they could easily produce the best 1080p screen out there and market it "being the best of everything: screen quality, battery preserving, heat reducing, and with the clearest whites". Instead they make a 4K screen which only runs at 4K when selected few apps are used. The rest of the time it is 1080p.

Sony don't have a leading behavior in the market either. So it can not make it's rivals jealous and switch to 4K, in order to adapt Android world into 4K rapidly. They simply don't have that influence, actually I believe next Sony phone will be 4K+ resolution with 2:1 ratio..

4) development support problem. Developers actually love companies who are developer friendly. Sony is the only company who release an AOSP code for almost every phone they release, also all of their phones come with lockable bootloader. Yet, they lag when it comes to kernel, Rom, mod etc. support. Somehow developers won't prefer Sony phones. Hell, they even fight with unlockable and frustrating Samsungs and don't show love for Sony for some reason.

Well, I trust these guys. They are giving people, who use their free time to make things better and share it with us for freely, and also sit here and respond to our never ending problems. If they don't prefer Sony most if the time I say they know something.

So, long story short; I am holding a phone in my hands right now. It has a super screen, nice build quality and good sound for music. Also comes with good battery life, dual speakers etc. But I can't trust the company behind it for the future. I can't use 3rd party camera apps, I can't use the full quality of the screen, camera and sound with my desired ROM, I can't use it to its full performance without it slowing down due to heating easily... Also, there are totally visible touch modules in the best screen of the world!

I will enjoy this phone till it's old enough, but then I'll never buy a Sony product again, as Sony is the only Japanese in the world who lost my respect. It'll go right next to Samsung in my blacklist.."