How To Fix Low incoming call volume on android smartphone

Disclaimer: This worked on my smartphone, and it should work on yours too. But do not experimente because you could damage your speaker. If sound is too loud, decrese it by Volume Down button while in middle of phone call.

Requirements: You will need a phone with MTK (Mediatek) chipset. If you are not sure, google your smartphone and search for information under CPU or CHIPSET. I do not know if it works with other chipsets.

Download MTKEngineerMode and install this app on yours android

or go to your phone dialer and tipe: *#*#3646633#*#*

• An EngineerMode will appear, swipe left to get to Hardware Testing, tap on Audio and than tap on Normal Mode.
• Audio_ModeSetting will appear as on picture.
• Select [sph]
  
• Change values:
  level 6 = 155 (origin value 136)
  level 5 = 140 (origin value 124)
  level 4 = 125 (origin value 112)
  level 3 = 110 (origin value 100)
  level 2 = 100 (origin value 88)
  level 1 = 86 (origin value 76)
  level 0 = 75 (origin value 64)
   
• Repeat the same for [sph2]

• Go back to Speech Enhancement
• Change Common Parametre to Normal Mode
• Select parametre 7, and set it to 96 (origin value 64)
• Select parametre 6, set to 300 (origin value 400), supposedly adds a bit more bass to the audio that's it. (Volume is significantly boosted and voice sounds more natural).