The sound volume seems to vary as much as a factor of four. I use a Bose speaker system to amplify the auxilliary output of my computer so I can hear the sound better than off the "El Cheapo Production" speakers in my laptop.
Particularly, I do most of my studying well into the late night, sometimes until 4:00 a.m.. I go to the opposite side of the house while my wife sleeps.
Some of the cards are so low in volume I raise the computer control so I can hear it. Some point latter, even in the same lesson, a card will come up that is so shockingly loud, it shakes me up as well wakes my wife four rooms away.
Shouldn't it be possible to run all the audio files through some mind of compressor-filter, and then set them to one standard setting?
Certainly, at the very least, your audio engineers should determine whatever they think is the optimal recording volume level, and then stick to it.
I might as well give you a heads up now, that within a couple years when a lot of us are going to be asking for Flashcard sharing between languages so us aspiring polyglots can study all of our hardest cards from all the Rocket courses we've ever taken this will be even more of a problem.
Right now I do not mind having to adjust the volume between Modules, or Languages, but it is a pain, to have such variation from within a single lesson.
I have just discovered a way to get my hardest Flashcards from many different lessons into one custom file. Once I've identified a problematic Flashcard, like the German ones that are three sentences long, I go back to the lesson area, and click the start that puts the whole sentence into the My Vocab. Then I can import them into the custom Flashcard sets. The wide variation of sound recording levels, and lack of a standard, quickly becomes apparent.
PS One of my mentors is famous for saying "The only sustainable competitive advantage a company will ever get is the ability to learn faster than its competitors."
Rocket should have a bright future given your willing to listen to and respond to such a continuous deluge of "suggestions for improvement." I hope you development team finds that such a passionate response from your customer-users is a wonderful thing not just a pain in the neck. The corporate landscape is littered with the carcasses of major multinational companies that were once number one, but are now gone.