diff --git a/synth/config_test.go b/synth/config_test.go
index e969a7e..f041e7f 100644
--- a/synth/config_test.go
+++ b/synth/config_test.go
@@ -16,10 +16,13 @@ func TestAllClassesHaveConfig(t *testing.T) {
 }
 
 func TestFrequenciesInRange(t *testing.T) {
+	const nyquist = float64(synth.SampleRate) / 2.0 // 22050 Hz
 	for class, cfg := range synth.ClassFreqConfigs {
-		// D-05: unknown buckets use 850-1100 Hz dissonant range; known classes use 60-800 Hz
-		if cfg.BaseHz < 60 || cfg.BaseHz > 1100 {
-			t.Errorf("class %q BaseHz=%.1f is out of range [60, 1100]", class, cfg.BaseHz)
+		if cfg.BaseHz <= 0 {
+			t.Errorf("class %q BaseHz=%.1f must be positive", class, cfg.BaseHz)
+		}
+		if cfg.BaseHz >= nyquist {
+			t.Errorf("class %q BaseHz=%.1f exceeds Nyquist (%.1f Hz)", class, cfg.BaseHz, nyquist)
 		}
 	}
 }
@@ -50,15 +53,7 @@ func TestPanPositionsInRange(t *testing.T) {
 	}
 }
 
-func TestClassFreqConfigsComplete(t *testing.T) {
-	for _, class := range classify.AllClasses() {
-		if _, ok := synth.ClassFreqConfigs[class]; !ok {
-			t.Errorf("ClassFreqConfigs missing entry for class %q", class)
-		}
-	}
-}
-
-func TestNumLayersMatchesAllClasses(t *testing.T) {
+func TestClassFreqConfigsMatchAllClasses(t *testing.T) {
 	if len(synth.ClassFreqConfigs) != len(classify.AllClasses()) {
 		t.Errorf("ClassFreqConfigs has %d entries but AllClasses() has %d entries",
 			len(synth.ClassFreqConfigs), len(classify.AllClasses()))