Rarities: A preview of the CTA 'L' Blue Line Railcar with Low Pitched Audio Announcements

Here's something rare: I took a ride on the CTA Blue Line 'L' and then the subway towards Irving Park and I discovered that the announcements (and the Ding-Dong! Doors Closing!) are low pitched so currently, the sound was in a melody of D, but when it's in a lower tone, it's almost around Db. I even rode a Brown Line car #3442 with the same lower tone.