[HTC U11  ROMs, Kernels, Recoveries, & Other Develo] Digitalkarma:
i felt it was time to share this and appropriately put this on my page. copying and paste from the op

Tutorial: How to adjust the decibel levels of the U-Sonic headphones

open the rom.zip of your choice that you are planning to use with 7zip. go to the system/etc directory and drag out the mixer_paths_tavil.xml onto your desktop. open the file with notepad++ or any xml editor and make the following changes..

to change the decibel volume of U-sonic with noise cancellation enabled look for the path name: anc-headphones inside tavil..

<path name="anc-headphones">
<ctl name="COMP1 Switch" value="0" />
<ctl name="COMP2 Switch" value="0" />
<ctl name="ANC Function" value="ON" />
<ctl name="ANC Slot" value="0" />
<ctl name="SLIM RX2 MUX" value="AIF4_PB" />
<ctl name="SLIM RX3 MUX" value="AIF4_PB" />
<ctl name="SLIM_6_RX Channels" value="Two" />
<ctl name="ADC MUX10" value="AMIC" />
<ctl name="AMIC MUX10" value="ADC3" />
<ctl name="ADC MUX12" value="AMIC" />
<ctl name="AMIC MUX12" value="ADC4" />
<ctl name="ANC0 FB MUX" value="ANC_IN_HPHL" />
<ctl name="ANC1 FB MUX" value="ANC_IN_HPHR" />
<ctl name="ADC3 Volume" value="8" />
<ctl name="ADC4 Volume" value="8" />
<ctl name="RX INT1_1 MIX1 INP0" value="RX2" />
<ctl name="RX INT2_1 MIX1 INP0" value="RX3" />
[B] <ctl name="RX1 Digital Volume" value="76" />
<ctl name="RX2 Digital Volume" value="76" />[/B]
<ctl name="ANC OUT HPHL Enable Switch" value="1" />
<ctl name="ANC OUT HPHR Enable Switch" value="1" />
</path>

change the RX1 and RX2 digital volumes to the number of your choice. the registered values are between '0' to '124'. '0' equals to -84 db's and '124 equals to +40 db's. I do not recommend you putting this at 124 or any number over 100 unless you want to risk damaging your ear or your headphones. :highfive:

on my rom i have it set at '84' but HTC set the default values at '74' or '76' depending which software version you are coming from.

to change the decibel volume of U-sonic with noise cancellation disabled look for the path name: headphones inside tavil..

<path name="headphones">
<ctl name="SLIM RX2 MUX" value="AIF4_PB" />
<ctl name="SLIM RX3 MUX" value="AIF4_PB" />
<ctl name="SLIM_6_RX Channels" value="Two" />
<ctl name="RX INT1_2 MUX" value="RX2" />
<ctl name="RX INT2_2 MUX" value="RX3" />
[B] <ctl name="RX1 Mix Digital Volume" value="76" />
<ctl name="RX2 Mix Digital Volume" value="76" />[/B]
</path>

once again change the RX Mix Digital Volume values to your liking from 0 to 124. i have also set these in my rom to '84' which is 0 db's, to get a louder but more neutral sound without compromising sound quality anything higher and you will get start to get distortion.

after you have made your changes save it then drag and drop your edited tavil.xml file back into the same directory where you extracted it from and overwrite the file inside your rom.zip with 7zip. close and reflash the rom.zip.

I'm sure there are some people in here who have used their U-sonic earphones and find that the default settings may not be set to their liking which is why i am sharing my findings with you. I have heard some say these earbuds are not loud enough and so i have worked on a solution. it's been almost two month since i discovered it. thanks to galactus for confirming and testing that it worked.

on a sidenote, if you want to change external speaker volume although i don't see why you will need to since the U11 speakers sound loud enough already as it is. You'll have to open up Mixer_Paths.xml and make the changes there. Look for speakers path and edit the values there, once again they are 0 to 124. HTC set it at 84 which is optimal level. i am not sure what speaker fluid and speaker db does. haven't had much testing done on that but if you want to test be my guest. Thanks to Galactus for confirming and testing the USonics