Update effect

effect.go

@@ -1,8 +1,28 @@
 package azuretts
 
+// The audio effect processor that's used to optimize the quality of the
+// synthesized speech output for specific scenarios on devices.
+//
+// For some scenarios in production environments, the auditory experience might
+// be degraded due to the playback distortion on certain devices.
+// For example, the synthesized speech from a car speaker might sound dull and
+// muffled due to environmental factors such as speaker response, room
+// reverberation, and background noise. The passenger might have to turn up the
+// volume to hear more clearly. To avoid manual operations in such a scenario,
+// the audio effect processor can make the sound clearer by compensating the
+// distortion of playback.
+//
+// Source: https://learn.microsoft.com/en-us/azure/ai-services/speech-service/speech-synthesis-markup-voice
 type Effect string
 
 const (
-	EffectEqCar         Effect = "eq_car"
+	// Optimize the auditory experience when providing high-fidelity speech in
+	// cars, buses, and other enclosed automobiles.
+	EffectEqCar Effect = "eq_car"
+
+	// Optimize the auditory experience for narrowband speech in telecom or
+	// telephone scenarios. You should use a sampling rate of 8 kHz. If the
+	// sample rate isn't 8 kHz, the auditory quality of the output speech isn't
+	// optimized.
 	EffectEqTelecomhp8k Effect = "eq_telecomhp8k"
 )