diff --git a/client.go b/client.go
index b1ad5ec..c130c9c 100644
--- a/client.go
+++ b/client.go
@@ -108,7 +108,7 @@ func (b *Barnard) connect(reconnect bool) bool {
 		}
 	})
 
-	// Initialize stereo encoder for file playback, reusing the one built for
+	// Initialize stereo encoder for two-channel capture and file playback, reusing the one built for
 	// the previous connection rather than allocating another.
 	if b.stereoEncoder == nil {
 		b.stereoEncoder = opus.NewStereoEncoder()
diff --git a/gumble/gumble/audio.go b/gumble/gumble/audio.go
index b99ad67..0547f1b 100644
--- a/gumble/gumble/audio.go
+++ b/gumble/gumble/audio.go
@@ -52,15 +52,22 @@ type AudioStreamEvent struct {
 // AudioBuffer is a slice of PCM audio samples.
 type AudioBuffer []int16
 
+// encoderForAudioBuffer is called with volatile held.
+func (client *Client) encoderForAudioBuffer(a AudioBuffer) AudioEncoder {
+	frameSize := client.Config.AudioFrameSize()
+	if client.AudioEncoderStereo != nil && (len(a) == frameSize*AudioChannels ||
+		(client.useStereoEncoder && len(a) != frameSize)) {
+		return client.AudioEncoderStereo
+	}
+	return client.AudioEncoder
+}
+
 func (a AudioBuffer) writeAudio(client *Client, seq int64, final bool) error {
 	// Encoding shares mutable codec state with server-configuration and file
 	// playback changes. Keep the client read lock through Encode and Reset so a
 	// stereo encoder cannot be replaced or reset while it is in use.
 	client.volatile.RLock()
-	encoder := client.AudioEncoder
-	if client.useStereoEncoder && client.AudioEncoderStereo != nil {
-		encoder = client.AudioEncoderStereo
-	}
+	encoder := client.encoderForAudioBuffer(a)
 	if encoder == nil {
 		client.volatile.RUnlock()
 		return nil
diff --git a/gumble/gumble/audio_stereo_test.go b/gumble/gumble/audio_stereo_test.go
new file mode 100644
index 0000000..fbe2e3f
--- /dev/null
+++ b/gumble/gumble/audio_stereo_test.go
@@ -0,0 +1,34 @@
+package gumble
+
+import (
+	"testing"
+	"time"
+)
+
+type testAudioEncoder struct{ channels int }
+
+func (*testAudioEncoder) ID() int                                  { return 4 }
+func (*testAudioEncoder) Encode([]int16, int, int) ([]byte, error) { return nil, nil }
+func (*testAudioEncoder) Reset()                                   {}
+
+func TestEncoderForAudioBufferPreservesStereoMicrophone(t *testing.T) {
+	for _, interval := range []time.Duration{10 * time.Millisecond, 20 * time.Millisecond, 40 * time.Millisecond, 60 * time.Millisecond} {
+		config := NewConfig()
+		config.AudioInterval = interval
+		mono, stereo := &testAudioEncoder{channels: 1}, &testAudioEncoder{channels: 2}
+		client := &Client{Config: config, AudioEncoder: mono, AudioEncoderStereo: stereo}
+		frameSize := config.AudioFrameSize()
+
+		if got := client.encoderForAudioBuffer(make(AudioBuffer, frameSize*AudioChannels)); got != stereo {
+			t.Errorf("%v: stereo microphone selected mono encoder", interval)
+		}
+		client.useStereoEncoder = true
+		if got := client.encoderForAudioBuffer(make(AudioBuffer, frameSize)); got != mono {
+			t.Errorf("%v: mono microphone selected stereo encoder during file playback", interval)
+		}
+		client.useStereoEncoder = false
+		if got := client.encoderForAudioBuffer(make(AudioBuffer, frameSize)); got != mono {
+			t.Errorf("%v: mono microphone selected stereo encoder", interval)
+		}
+	}
+}
diff --git a/gumble/gumble/client.go b/gumble/gumble/client.go
index 6b7705f..f49b341 100644
--- a/gumble/gumble/client.go
+++ b/gumble/gumble/client.go
@@ -399,7 +399,7 @@ func (c *Client) Send(message Message) {
 	message.writeMessage(c)
 }
 
-// SetStereoEncoder installs the encoder used for stereo file playback.
+// SetStereoEncoder installs the encoder used for stereo capture and file playback.
 func (c *Client) SetStereoEncoder(encoder AudioEncoder) {
 	c.volatile.Lock()
 	defer c.volatile.Unlock()
@@ -458,9 +458,8 @@ func (c *Client) UDPActive() bool {
 	return c.udpActive
 }
 
-// DisableStereoEncoder switches back to mono encoding for voice and
-// resets the stereo encoder so stale state does not bleed into the
-// next file playback.
+// DisableStereoEncoder clears file playback mode and resets the stereo
+// encoder. Stereo microphone frames still select it by channel count.
 func (c *Client) DisableStereoEncoder() {
 	c.volatile.Lock()
 	defer c.volatile.Unlock()
diff --git a/gumble/gumbleopenal/stream.go b/gumble/gumbleopenal/stream.go
index b00ba24..f91f132 100644
--- a/gumble/gumbleopenal/stream.go
+++ b/gumble/gumbleopenal/stream.go
@@ -1064,21 +1064,10 @@ func (s *Stream) sourceRoutine(inputDevice *string, stop chan bool, done chan st
 					recorder.RecordAudioFrame(recorderOutgoingSource, outputBuffer, true)
 				}
 			} else if hasMicInput {
-				// Send mic when no file is playing. If the microphone is
-				// stereo, downmix to mono since Mumble voice transmission
-				// uses mono Opus encoding.
-				outBuf := int16Buffer
-				if s.sourceChannels == 2 {
-					monoBuf := make([]int16, frameSize)
-					for i := 0; i < frameSize; i++ {
-						// Average left and right channels
-						monoBuf[i] = int16((int32(int16Buffer[i*2]) + int32(int16Buffer[i*2+1])) / 2)
-					}
-					outBuf = monoBuf
-				}
-				outgoing <- gumble.AudioBuffer(outBuf)
+				// Preserve the capture device's channel layout for encoding.
+				outgoing <- gumble.AudioBuffer(int16Buffer)
 				if recorder := s.getRecorder(); recorder != nil {
-					recorder.RecordAudioFrame(recorderOutgoingSource, outBuf, false)
+					recorder.RecordAudioFrame(recorderOutgoingSource, int16Buffer, s.sourceChannels == 2)
 				}
 			}
 		}
diff --git a/gumble/opus/opus.go b/gumble/opus/opus.go
index 0eab4df..8a1fe27 100644
--- a/gumble/opus/opus.go
+++ b/gumble/opus/opus.go
@@ -10,7 +10,7 @@ var Codec gumble.AudioCodec
 
 const (
 	ID            = 4
-	VoiceChannels = 1 // Force mono for voice transmission
+	VoiceChannels = 1 // Channel count for the mono encoder
 )
 
 func init() {
@@ -27,7 +27,7 @@ func (*generator) ID() int {
 }
 
 func (*generator) NewEncoder() gumble.AudioEncoder {
-	// Force mono for voice transmission
+	// Create the mono encoder for single-channel capture.
 	e, _ := opus.NewEncoder(gumble.AudioSampleRate, VoiceChannels, opus.AppVoIP)
 	return &Encoder{
 		Encoder:  e,
@@ -35,9 +35,8 @@ func (*generator) NewEncoder() gumble.AudioEncoder {
 	}
 }
 
-// NewStereoEncoder creates a stereo encoder for file playback
+// NewStereoEncoder creates a stereo encoder for capture and file playback.
 func NewStereoEncoder() gumble.AudioEncoder {
-	// Create stereo encoder for file playback
 	e, _ := opus.NewEncoder(gumble.AudioSampleRate, gumble.AudioChannels, opus.AppAudio)
 	return &Encoder{
 		Encoder:  e,