diff --git a/device/alsa/alsa.go b/device/alsa/alsa.go
index eadf7bd3..72b643a1 100644
--- a/device/alsa/alsa.go
+++ b/device/alsa/alsa.go
@@ -466,6 +466,8 @@ func (d *ALSA) formatBuffer() pcm.Buffer {
 	return formatted
 }
 
+// DataSize returns the size in bytes of the data ALSA device d will
+// output in the duration of a single recording period.
 func (d *ALSA) DataSize() int {
 	return pcm.DataSize(d.SampleRate, d.Channels, d.BitDepth, d.RecPeriod, d.Codec)
 }