diff --git a/premix.c b/premix.c
index f637cb4..7d6aa99 100644
--- a/premix.c
+++ b/premix.c
@@ -481,6 +481,7 @@ pcm_convert (const ddb_waveformat_t * restrict inputfmt, const char * restrict i

         if (outchannels != outputfmt->channelmask) {
             // some of the channels are not used
+            printf ("outchannels=%d, channelmask=%d -> mismatch, will output 1st channel\n", outchannels, outputfmt->channelmask);
             memset (output, 0, nsamples * outputsamplesize);
         }