a) write an expression for the discrete time signal, assuming sampling at 44.1 khz. what is the digital frequency? is it inside the principal range? (20 points) b) assume that to save hard drive space, the recording studio records mariah’s singing at 1/15 of the standard sampling frequency. when the recording is played back, what will it sound like? what is the closest note to the aliased reconstructed signal? (10 points) c) what sampling frequency (or frequencies) could be used so that the playback (i.e. the reconstructed signal) is a "middle c" on the piano (c4)? (10 points)