This was an answer to the Atari 2600's inability to play "voice files"... this was connected to the second joystick port of the Atart 2600 using a special interface cable, and played tapes for 2 specific games ... "Smurf's save the day" (which came with the module) and "Bernstein Bears" (sold seperatly) - these were the only two games ever released for use with this system.
The player would insert a special audio tape in the cassette deck, connect the cable to the jacks on the lower left (the jack used both the microphone and speaker jack - but left the headphone jack open, read on as to why) - then press play - noting the cassette player would not move until the Atari VCS was turned on and the correct game cartridge was inserted....
The tapes were "Stereo" Tapes - but used the left channel for audio signals to the Atari, and the right channel to play the recorded audio out the mono speaker...
If you are wanting to get rid of this one, I am happy chat about an offer. (if you still have it of course)