jeeva … guess you are referring to microsoft's alarm&clock app which is included with win-10 os.
the media-file in question is located in c/windows/media directory … "Alarm01" is default. it is a *.wav file … *.mp3 files do not work. i trimmed one of my full-length *.mp3 songs (led-zeppelin) down to a five-second file … converted that file to wav-file … this was all done online through a website called 123apps.com … which offers the free service.
now the only thing remaining was to rename(Alarm01_old) the default-alarm so i could properly name(Alarm01) as the newly created wav file. and this step needs security-clearance (via permissions). one word of caution, jeeva … altering permissions within the os can allow hackers easy entry … altering too many parameters/permissions could manifest unstable environment.
so … i will let you figure out that last bit of magic on your own.
i have also read there is a method utilizing the windows-registry … again, i will not share those parameters with you … for the same reason as above. let google be your ally.
almost forgot … 123apps.com … when you download the resultant files … make sure you scan them for virus/malware … virustotal.com can be your friend in this regard.
as so often happens … sometimes people get in over their heads when clicking this 'n that and the next thing. so, to avoid this calamity … before you start clicking "nilly-willy" … create system-restore point. that way, you can safely return to where you started. you have the option to remove that system-restore point tomorrow … if everything is working okay.
After doing some searching, I found another potential solution that doesn't involve Registry tweaks and hacks as jack mentions may be risky.
Go to Settings > Personalization > Sounds
On the left hand side of the screen, under Personalization, select THEMES
In the middle of the screen, select Related Settings > Advanced Sound Settings
This opens up the traditional Windows Sound dialog box used in earlier versions of windows
Choose the Sounds tab, and under "Sounds Scheme" make certain that the setting is "Windows Default" and not "No Sounds"
Under the Programs Events section, look for the "Calendar Reminder" item
Click on the item with your mouse to select, and then under the section below called "Sounds" you will see an item called "Windows Notification Sound" and click it to select with your mouse
You'll see a small Green or Grey right-pointing arrow that says "Test"; click the Test button to play the default sound for that item, it should play a brief tone which is the "Windows Notification Sound" you'll hear through your computer speakers
To change the default sound to one of your creation *I did it with a downloaded .wav file called starwars.wav*, use the Browse button to navigate to the place in your Library folders where that custom .wave file you want to have played is stored. In my PC it's under C:\Users\Username\Music
Select and click the name of your .wav sound file, and then hit the Green/Grey Test button to play the sound on your computer to ensure it's the correct sound or song
Looking at the top of the same dialog box we've been working in (Sounds), go back to the "Sound scheme" section at the top of the box, and click the SAVE AS button, and give the new modified sound scheme a name such as "Windows Alarm Test1" . This will save the sound scheme with the modified sound file (your new .wav file) into that scheme name with the new .wav sound
Now click OK, and close that dialog box out
Next, you need to use W10 to set your Alarm Time and test it
Do this, by clicking on your W10 start (White Flag on taskbar), look for Alarms & Clock on the Apps List under _A_. Click on that item to open it
Under the Icon Selector at the top of this screen, click on the Alarm icon
Click on the Alarm on whatever time it has such as mine: 10:48AM, with a message of Good Morning, Every Day with a slide button set to ON by default
Click on the Alarm item to open it, and use the Dial selector to set your Alarm time, and AM or PM under Edit Alarm
Under Alarm Name you can change it to your .wav file name, mine is starwars.wav
Under the Sound item, click to open your choices; there are 10 by default
However, none of them correspond to the new .wav file.
On the bottom right of the dialog box, click the floppy disk icon for save, and save the new Alarm item
Close the dialog box
To test, I set the Alarm 3 minutes into the future, and wait for the notification window to popup on my W10 desktop which is does fine; however it plays only 1 of the 10 default sounds, which you can test play when selecting, and not my .wav file (starwars.wav)
Hopefully, that may work on your computer!
If it does, please post back so I can share this solution with our other forum users looking for a solution to this problem. I developed it just for you. The reason is doesn't play the right sound is unknown to me at this time; but I have 7 other W10 computers to try it on. If it works on at least 1 or more of them, it's worth telling folks about. Perhaps it will work on some PCs but not others.
The good news here, is that you can at least change it from the W10 default which is the CHIMES tone to any of the 9 other defaults built-into W10 Alarm & Clock!
The bad news is that it doesn't fix your problem about using your ringtone or other favorite .wav song or file like you asked. I apologize for that.
There also may be some free 3rd party apps that may provide that functionality, but since this is a new problem reported in W10 (I've been a Tester for 2-1/2 years) and have never run into it on my own or any of the 4 tech forums I help out on. I'll keep searching and so will others here who read my thread, and that may be a solution that one of our talented developers may tackle and provide us with a little app to fix this. So give it a try and let us know if it works for you. If not, we'll keep our fingers crossed and see if further testing shows the procedure will work on at least some W10 PCs.
Also, I started working on your problem 2 days ago, but due to being laid up in bed for nearly 2 weeks with a low-back problem, I didn't get it done until today.