diff --git a/doc/4-instrument/fm-opz.md b/doc/4-instrument/fm-opz.md
index 26ee11946..dbfbbe9ef 100644
--- a/doc/4-instrument/fm-opz.md
+++ b/doc/4-instrument/fm-opz.md
@@ -43,7 +43,7 @@ these apply to each operator:
 ![FM ADSR chart](FM-ADSRchart.png)
 
 - **Envelope Scale (RS/KS)**: also known as "Rate Scale" or "Key Scale". determines the degree to which the envelope execution speed increases according to the pitch (0 to 3).
-- **Frequency Multiplier (MULT)**: sets the coarse pitch offset in relation to the note (0 to 15). 0 is -1 octave, 1 is 0 octaves, 2 is 1 octave, 3 is 1 octave 7 semitones, and so on.
+- **Frequency Multiplier (MULT)**: sets the coarse pitch offset in relation to the note (0 to 15). The values follow the harmonic scale. For example, 0 is -1 octave, 1 is 0 octaves, 2 is 1 octave, 3 is 1 octave 7 semitones, and so on.
 - **Fine Frequency Multiplier (Fine)**: a fine control for MULT.
 - **Envelope Generator Shift (EGS)**: adds a "handicap" to the envelope. in other words, the minimum volume of the operator.
   - 0: no change