An experiment with Memory

My credit card got accidentally damaged, and I recently received a new credit card, and a day later, a post arrived with the 4 digit pin to authenticate the card. I (thought I had :) memorized the pin, but a couple of days later, I couldn't recall it. 

I'm not sure why this idea occurred to me - I looked at the 4 digits and  decided to map them to musical notes. 

0 would be lower Ni 

1 would be lower Sa 

2 would be Re 

3 would be Ga

...

8 would be upper Sa 

9 would be upper Re 

I mentally imagined myself  played the notes corresponding to the digits in the pin, on the keyboard. A few days later,  I could easily recall the notes, and thus, the pin ! 

I have a good memory for notes, but it had never occurred to me use them to memorize digit sequences. Do you have a good memory for something ? Can you create an association between whatever you wish to memorize, and your pre-existing domain where your memory is already good ? It seems so obvious, now that I put this down in writing, but I had never tried this earlier :)