I have an S7 and use the Samsung Music app to play mp3's on it, I got the app free from the Google Play Store. Before I do anything else I run my mp3 files through a free program called MP3 Gain to adjust the volume levels of all of the files to 94 db. This makes all of the files play at the same volume during playback. Without adjusting the files with MP3 Gain some of the files in an MP3 folder will play louder than others and it is a pain to have to constantly adjust the volume on my car radio or phone all the time. MP3 Gain's default is 89 db but I experimented and found 94 db is the best setting to level out the volume and cut out distortion while still preserving the quieter passages in the files.
Nearly all of my music library is at 256, 256 VBR or 320 kbps. My phone only has 20GB of storage so I use another free program called Media Human Audio Convertor to change the bit rates down to 128 kbps so I can put a lot more songs on the phone. I tried using an SD card for music storage on my phone but the card I bought must have been bad because I could not format it and neither my phone or laptop would even recognize it. I have not tried another SD card because 20 GB at 128 kbps is much more than enough storage space for plenty of files.
After converting the files to 128 kbps I plug the phone into my laptop and navigate to the Playlists folder on it, then open the "New Folder" folder and copy the MP3 files I want there. I don't notice any difference in sound quality between 128 kbps files and 320 kbps files on my phone. The Samsung Music app is very easy to use, I tried the VLC player before it but I like the Samsung app a lot better. VLC had a built in equalizer with a preamp that really did not sound good at all. Samsung Music lets me use the equalizer that is already on the phone in the sound settings menu, and I dialed it in to sound the way I like it. The "Rock" preset sounds good but I just use the standard bass/treble and vocal/instrument dials. I have not needed to change anything on the eq settings since I set it up.
I don't play mp3's in my car through my phone, because the radio does not allow me to change tracks or albums. With my factory radio I would have to pick up the phone, unlock it with my PIN and then use the music app to change albums or advance tracks and I think that is unsafe to do while driving. In the car I just use a flash drive that I can control with the radio. I do use the phone to play MP3's is here at home when I am working or doing stuff around the house. It sounds great with a set of Sony earbuds. I also have a blue tooth speaker I use in my home office and a set of blue tooth headphones and the files sound great with either one of those.
