The last analog audio storage medium I used was audio cassette tape, and such devices do indeed require an ADC (analog-to-digital converter, such as in a sound card with audio input) to digitize the audio when importing it into a computer. However, for some time now (since mp3 players replaced portable audio cassette players), the sound data is stored in digital format, so no ADC needed (just a DAC) to play it. Analog on cassette tape, but digital all the way to just before the speakers or headset (which need analog audio to drive them), though in some cases audio transducers (speakers) can be driven directly with digital PWM and they do a mechanical digital-to-analog conversion all by themselves due to mechanical inertia (in which case there are no analog audio signals anywhere in the system).
The kindles do not contain analog data storage. Though some cameras do indeed contain analog values in their
CCD image sensor). In fact, high-density flash devices are already storing multiple voltage levels, in a hybrid sort of way (i.e.
MLC memory), but still not analog like CCD.