diff --git a/lumps/genmidi/config.py b/lumps/genmidi/config.py
index da8bb494..43c1ca07 100644
--- a/lumps/genmidi/config.py
+++ b/lumps/genmidi/config.py
@@ -45,6 +45,15 @@
 #
 #   Instrument("file1.sbi", "file2.sbi")
 #
+# To tune the instruments, it's possible to apply an offset to the notes
+# that are played. For example, to force all notes down by one octave:
+#
+#   Instrument("file1.sbi", off1=-12)
+#
+# This can be controlled individually for double-voice instruments, eg.
+#
+#   Instrument("file1.sbi", "file2.sbi", off1=-12, off2=+6)
+#
 # When an instrument is played, the note usually comes from the MIDI
 # event. Some instruments (especially percussion) always play the same
 # note. To specify a fixed note, do this:
diff --git a/lumps/genmidi/instrument.py b/lumps/genmidi/instrument.py
index 66cca2e8..f42917fc 100644
--- a/lumps/genmidi/instrument.py
+++ b/lumps/genmidi/instrument.py
@@ -72,7 +72,7 @@ def load_instrument(filename):
 	return result
 
 class Instrument:
-	def __init__(self, file1, file2=None, note=None):
+	def __init__(self, file1, file2=None, off1=0, off2=0, note=None):
 		self.instr1 = load_instrument(file1)
 
 		if file2 is not None:
@@ -81,6 +81,8 @@ class Instrument:
 			self.instr2 = None
 
 		self.fixed_note = note
+		self.offset1 = off1
+		self.offset2 = off2
 
 NullInstrument = Instrument("dummy.sbi")