Add linear fade-out to IRs with --fade-ms option (default 5ms); update README and CLI

pkg/convolve/convolve.go

@@ -322,3 +322,22 @@ func Resample(data []float64, fromSampleRate, toSampleRate int) []float64 {
 
 	return result
 }
+
+// FadeOutLinear applies a linear fade-out to the last fadeSamples of the data.
+// fadeSamples is the number of samples over which to fade to zero.
+func FadeOutLinear(data []float64, fadeSamples int) []float64 {
+	if fadeSamples <= 0 || len(data) == 0 {
+		return data
+	}
+	if fadeSamples > len(data) {
+		fadeSamples = len(data)
+	}
+	out := make([]float64, len(data))
+	copy(out, data)
+	start := len(data) - fadeSamples
+	for i := start; i < len(data); i++ {
+		fade := float64(len(data)-i) / float64(fadeSamples)
+		out[i] *= fade
+	}
+	return out
+}