diff --git a/smnp/module/synth/function/synth.py b/smnp/module/synth/function/synth.py
index 7002310..0ae66a4 100644
--- a/smnp/module/synth/function/synth.py
+++ b/smnp/module/synth/function/synth.py
@@ -1,20 +1,65 @@
+from smnp.error.runtime import RuntimeException
 from smnp.function.model import Function, CombinedFunction
 from smnp.function.signature import varargSignature
 from smnp.module.synth.lib.wave import play
 
 from smnp.type.model import Type
 from smnp.type.signature.matcher.list import listOf
-from smnp.type.signature.matcher.type import ofTypes
+from smnp.type.signature.matcher.type import ofTypes, ofType
 
-_signature1 = varargSignature(listOf(Type.NOTE, Type.INTEGER))
-def _function1(env, notes):
+
+DEFAULT_BPM = 120
+DEFAULT_OVERTONES = [0.4, 0.3, 0.1, 0.1, 0.1]
+
+
+def getBpm(config):
+    key = Type.string("bpm")
+    if key in config.value:
+        bpm = config.value[key]
+        if bpm.type != Type.INTEGER or bpm.value <= 0:
+            raise RuntimeException("The 'bpm' property must be positive integer", None)
+
+        return bpm.value
+
+    return DEFAULT_BPM
+
+
+def getOvertones(config):
+    key = Type.string("overtones")
+    if key in config.value:
+        overtones = config.value[key]
+        rawOvertones = [overtone.value for overtone in overtones.value]
+        if overtones.type != Type.LIST or not all(overtone.type == Type.FLOAT for overtone in overtones.value):
+            raise RuntimeException("The 'overtones' property must be list of floats", None)
+
+        if len(rawOvertones) < 1:
+            raise RuntimeException("The 'overtones' property must contain one overtone at least", None)
+
+        if any(overtone < 0 for overtone in rawOvertones):
+            raise RuntimeException("The 'overtones' property mustn't contain negative values", None)
+
+        if sum(rawOvertones) > 1.0:
+            raise RuntimeException("The 'overtones' property must contain overtones which sum is not greater than 1.0", None)
+
+        return rawOvertones
+
+    return DEFAULT_OVERTONES
+
+
+_signature1 = varargSignature(listOf(Type.NOTE, Type.INTEGER), ofType(Type.MAP))
+def _function1(env, config, notes):
     rawNotes = [note.value for note in notes]
-    play(rawNotes, env.findVariable("bpm").value, env.findVariable("overtones").value)
+    bpm = getBpm(config)
+    overtones = getOvertones(config)
+
+    play(rawNotes, bpm, overtones)
 
 
-_signature2 = varargSignature(ofTypes(Type.NOTE, Type.INTEGER))
-def _function2(env, notes):
-    play([ notes ], env.findVariable("bpm").value, env.findVariable("overtones").value)
+_signature2 = varargSignature(ofTypes(Type.NOTE, Type.INTEGER), ofType(Type.MAP))
+def _function2(env, config, notes):
+    bpm = getBpm(config)
+    overtones = getOvertones(config)
+    play([ notes ], bpm, overtones)
 
 
 function = CombinedFunction(
diff --git a/smnp/module/synth/lib/wave.py b/smnp/module/synth/lib/wave.py
index 8259423..5df57be 100644
--- a/smnp/module/synth/lib/wave.py
+++ b/smnp/module/synth/lib/wave.py
@@ -46,7 +46,7 @@ def sineForNote(note, bpm, overtones):
 
 
 def sound(frequency, duration, overtones):
-    return sum(a.value * sine((i+1) * frequency, duration) for i, a in enumerate(overtones))
+    return sum(a * sine((i+1) * frequency, duration) for i, a in enumerate(overtones))
 
 
 def sine(frequency, duration):