Shulchan Aruch HaRav Hilchos Talmud Torah 3:12 says in part:
וכל אדם צריך ליזהר להוציא בשפתיו ולהשמיע לאזניו כל מה שלומד בין במקרא משנה ותלמוד אלא אם כן בשעת עיון להבין דבר מתוך דבר וכל מה שלומד בהרהור לבד ואפשר לו להוציא בשפתיו ואינו מוציא אינו יוצא בלימוד זה ידי חובת מצות ולמדתם אותם
And every person has to be careful to say the words with his lips and hear them with his ears in all that he learns whether Mikra, Mishna or Talmud, except at a time of thinking to understand the underlying concepts. Everything that he learns with thinking alone and he was able to say them with his lips but fails to doesn't fulfill with this learning the obligation of the Mitzvah of "And you shall learn them ..."
The author of the footnote points to the Tzemach Tzedek in אור התורה why says the distinction is that "it is impossible to talk." In other words, if learning cannot be accomplished through speaking, as opposed to choosing to remain silent, then it is still learning.
That would seem to apply to Torah tapes.
Note that according to the Tafnas Paneiach quoted here there are two distinct parts of the Mitzvah - one is to know Torah, the other is to learn it. It is only the latter that may have the requirement of saying the words, but the former is sufficient to make a Siyum, so that someone can make a siyum on learning from Torah Tapes is not dispositive of the question of if it is Talmud Torah.