Lynn,
The listening sessions are scheduled to be completed within one day. Usually a character speaks or is interviewed at one time and then the session moves on to a new character. The characters are all listed in separate boxes meaning that there is jumping from box to box as the next character is introduced. Typically, the characters are listed in the order that they appear in the listening session (to make things a bit easier for the students).

Not all characters require note-taking though, as some minor characters are omitted.
At times, other commentators in the audio provide further details about the characters, but this is typically at the very beginning of the session or right before or after the person is interviewed. Pausing and relistening, or pausing to write is a necessary component of the lesson. So, plan for that before you begin.
Also, some of the audios are more easily heard than others, so be sure that your son knows he is not meant to catch everything (as otherwise he will quickly become frustrated with the activity). Think of this more as an activity meant to provide a "feel for the times" as well as helping kiddos generally become a bit more familiar with the key players in each scenario.

The audios are actually reproductions of the CBD old-time radio shows, and as such they do not have the stellar quality we are used to in listening to audios today. Listening on the computer with headphones seems to best at our house.

Although, when I listen I just listen directly from my computer without headphones.
Also, each listening session is approximately 30 min., and by the time kiddos pause/write/relisten if needed it can take 45 min. or to complete (with the opinion box included). My oldest son used to listen to his sessions in the evening as he found it was quieter then. My next oldest son just does his in the school day when it comes up.
In your son's case I think the least frustration might come from the following two choices: Either you or your husband could listen along with your son and take notes as he dicates them to you. Or, you could instead just have your son listen to the entire session without stopping, and then share whatever he happens to remember from each character for you to scribe for him in his notebook after the session is over. At that juncture, if he doesn't remember much about each character you would have to be alright with that, as listening will have provided him with a fuller, richer picture of the time and at least an introduction to the key players. Either way, at the end he will have to give his opinion about the event and characters, which is actually is an important skill that will stretch him (and is a goal that can be accomplished whether you listen along with him or not.) Just be sure he gives his own opinion rather than formulating one he thinks he should have.

Giving one's opinion can be difficult when asked to support it.
With your son's needs in mind, it can be interesting to sort through the most important goal in each assignment for him. I applaude your amazing efforts! (and his)!
Blessings,
Carrie