As an owner of the i9500 I was annoyed from the really low quality of call I was having. I tried the latest modems but had no luck in enabling the HD audio as was mentioned here
Here is how I managed to improve my voice call - I have no idea if it will work for others with I9500 - but please if it does for you, do tell
1) Download the I9500 XXUBMEA modem (I9500_XXUBMEA_MODEM.rar) from here or here (source). extract the I9500_XXUBMEA_MODEM.tar.md5 from it.
2) put your S4 in ODIN mode (power off, press the volume-down + home key + power button, a warning appears, let go of the keys, press volume up)
3) start ODIN. (I used ODIN 3.07 but I assume any will work), Press the "phone" button, select the I9500_XXUBMEA_MODEM.tar.md5 file. check the auto reboot option. press start.
4) this was my ODIN log:
<ID:0/004> File analysis.. <ID:0/004> SetupConnection.. <ID:0/004> Initialzation.. <ID:0/004> Get PIT for mapping.. <ID:0/004> Firmware update start.. <ID:0/004> modem.bin <ID:0/004> NAND Write Start!! <ID:0/004> Transmission Complete.. <ID:0/004> Now Writing.. Please wait about 2 minutes <ID:0/004> Receive Response from boot-loader <ID:0/004> RQT_CLOSE !! <ID:0/004> RES OK !! <ID:0/004> Removed!! <ID:0/004> Remain Port .... 0 <OSM> All threads completed. (succeed 1 / failed 0)
5) if successful, the phone will reboot. in my case it started but the mobile network was not working anymore. no problems.
5) time for service mode. Dial *#0011#
6) press menu key, than "back".
7) You're now in debug screen. press the menu key and "back". welcome to service mode
8) press the menu key and select 8 (Which is selecting the "WB-AMR status)
9) it should say
WB-AMR SETTING: 1(ON)
GSM WB: OFF(14)
UTMS WB: ON(10)
if that is the case, congratulations you just enabled the WB-AMR (well, you didn't but the firmware you installed did).
11) get the XXUFNC1 radio (i9500_RADIO_XXUFNC1.zip) from here. if you're using a computer, copy it to the the phone
12) power off the phone. reboot into recovery (volume-up + home key + power key, let go when you see the Samsung logo). I have CWM-based recovery V220.127.116.11
13) select "install zip" and select the i9500_RADIO_XXUFNC1.zip file.
14) reboot your phone (and fix root).
15) sound quality should be better now.
It improved my call sound quality - if it worked for you please share
I tried the "latest" Chinese modem (i9500_RADIO_ I9500ZCUGND1) and the sound quality was horrible... don't use it