Update audio-control.html (#4295)

Closes #4230

Added clarity to the existing language for "direct result of user's
intentional activation" and added text specific to a conference call.

---------

Co-authored-by: Patrick H. Lauke <[email protected]>

Author: mbgower

understanding/20/audio-control.html

@@ -41,7 +41,7 @@ <h2>Intent of Audio Control</h2>
          </p>
       </div>
       <p>See also <a href="low-or-no-background-audio">1.4.7 Low or No Background Audio</a>.</p>
-      <p>In the context of this Success Criterion, "plays automatically" broadly refers to audio that is not started/played as a direct result of a user's intentional activation. For example, not selecting a link or button.</p>
+      <p>In the context of this success criterion, "plays automatically" broadly refers to audio that is not started/played as a direct result of a user's intentional activation. For example, selecting a link or button with clear labelling or context that it will start an experience where audio will play is an example of starting in response to a user's intended action. This criterion is also not intended to apply to a conference call or other interaction where two-way voice communication may take place; the potential for any participant to speak during a conference call is not equivalent to audio that "plays automatically for more than 3 seconds." However, a mechanism to control the volume of conference call output independently from the overall system volume would be a best practice.</p>
    </section>
    <section id="benefits">
       <h2>Benefits of Audio Control</h2>