instructor-audio: Add latency checker and good values

Author: rkdarst

instructor-audio.md

@@ -4,6 +4,8 @@ Audio quality, and balance between instructors, is *absolutely
 critical* to good online work, especially teaching.  Consider the
 following:
 
+## Checklist
+
 * Can you adjust your microphone volume from very low to
   higher-than-needed?  Make sure your dynamic range is larger than
   "barely working", so that you have some room to adjust for later.
@@ -35,3 +37,28 @@ following:
   headset.
 * Set your microphone's hardware volume to something relatively high -
   and control via the software.
+
+
+## Latency tester
+
+You can use this web app latency tester
+<https://nullvoxpopuli.github.io/latency-tester/> to check your
+headset's latency.
+
+* Use the tester.  Try to click the button in sync with the beats.
+  You'll be delayed in the first few beats, but will soon sync up and
+  after 10 beats you'll get an accurate reading.
+* Target values
+  * A good value for wired headphones is less than 50ms (it can be
+    within the margin of error of zero!).
+  * A good value for low-latency wireless (dedicated dongle) is
+    100-200ms
+* Other example values
+  * 1000-1500ms: The 100-200ms headphones also have a high-quality,
+    high-latency mode when the microphone is not being captured.  The
+    latency is over one second.
+
+* Just consider the difference now, between having a discussion with
+  someone and having 1.5s round-trip latency between compared to 200ms
+  round-trip latency (adding some for Zoom latency - which can be
+  quite small on good connections).