diff --git a/libavfilter/avf_showspectrum.c b/libavfilter/avf_showspectrum.c
index 3611c96a5e..88bee3cb6e 100644
--- a/libavfilter/avf_showspectrum.c
+++ b/libavfilter/avf_showspectrum.c
@@ -590,7 +590,7 @@ static int plot_spectrum_column(AVFilterLink *inlink, AVFrame *insamples)
                 a = cbrt(a);
                 break;
             case FOURTHRT:
-                a = pow(a, 0.25);
+                a = sqrt(sqrt(a));
                 break;
             case FIFTHRT:
                 a = pow(a, 0.20);