diff --git a/doc/4-instrument/fm-opl.md b/doc/4-instrument/fm-opl.md
index 1697128ea..00bf51f85 100644
--- a/doc/4-instrument/fm-opl.md
+++ b/doc/4-instrument/fm-opl.md
@@ -33,7 +33,7 @@ These apply to each operator:
 - **Attack Rate (AR)**: determines the rising time for the sound. The bigger the value, the faster the attack (0 to 15).
 - **Decay Rate (DR)**: Determines the diminishing time for the sound. The higher the value, the shorter the decay. It's the initial amplitude decay rate (0 to 15).
 - **Sustain Level (SL)**: Determines the point at which the sound ceases to decay and changes to a sound having a constant level. The sustain level is expressed as a fraction of the maximum level (0 to 15).
-- **Release Rate (RR)**: Determines the rate at which the sound disappears after KEY-OFF. The higher the value, the shorter the release (0 to 15).
+- **Release Rate (RR)**: Determines the rate at which the sound disappears after note off. The higher the value, the shorter the release (0 to 15).
 - **Total Level (TL)**: Represents the envelope’s highest amplitude, with 0 being the largest and 63 (decimal) the smallest. A change of one unit is about 0.75 dB.
 - **Key Scale Level (KSL)**: Also known as "Level Scale". Determines the degree to which the amplitude decreases according to the pitch.
 
diff --git a/doc/4-instrument/fm-opll.md b/doc/4-instrument/fm-opll.md
index fcd828fe4..efe6100b2 100644
--- a/doc/4-instrument/fm-opll.md
+++ b/doc/4-instrument/fm-opll.md
@@ -35,7 +35,7 @@ These apply to each operator:
 - **Attack Rate (AR)**: determines the rising time for the sound. The bigger the value, the faster the attack (0 to 15).
 - **Decay Rate (DR)**: Determines the diminishing time for the sound. The higher the value, the shorter the decay. It's the initial amplitude decay rate (0 to 15).
 - **Sustain Level (SL)**: Determines the point at which the sound ceases to decay and changes to a sound having a constant level. The sustain level is expressed as a fraction of the maximum level (0 to 15).
-- **Release Rate (RR)**: Determines the rate at which the sound disappears after KEY-OFF. The higher the value, the shorter the release (0 to 15).
+- **Release Rate (RR)**: Determines the rate at which the sound disappears after note off. The higher the value, the shorter the release (0 to 15).
 - **Total Level (TL)**: Represents the envelope’s highest amplitude, with 0 being the largest and 63 (decimal) the smallest. A change of one unit is about 0.75 dB.
   - in the case of the second operator, it goes from 0 to 15 instead.
 - **Key Scale Level (KSL)**: Also known as "Level Scale". Determines the degree to which the amplitude decreases according to the pitch.
diff --git a/doc/4-instrument/fm-opm.md b/doc/4-instrument/fm-opm.md
index a3db0b795..dc5c7f922 100644
--- a/doc/4-instrument/fm-opm.md
+++ b/doc/4-instrument/fm-opm.md
@@ -35,7 +35,7 @@ These apply to each operator:
 - **Decay Rate (DR)**: Determines the diminishing time for the sound. The higher the value, the shorter the decay. It's the initial amplitude decay rate (0 to 31).
 - **Sustain Level (SL)**: Determines the point at which the sound ceases to decay and changes to a sound having a constant level. The sustain level is expressed as a fraction of the maximum level (0 to 15).
 - **Decay Rate 2 (D2R) / Sustain Rate (SR)**: Determines the diminishing time for the sound. The higher the value, the shorter the decay. This is the long "tail" of the sound that continues as long as the key is depressed (0 to 31).
-- **Release Rate (RR)**: Determines the rate at which the sound disappears after KEY-OFF. The higher the value, the shorter the release (0 to 15).
+- **Release Rate (RR)**: Determines the rate at which the sound disappears after note off. The higher the value, the shorter the release (0 to 15).
 - **Total Level (TL)**: Represents the envelope’s highest amplitude, with 0 being the largest and 127 (decimal) the smallest. A change of one unit is about 0.75 dB.
 
 ![FM ADSR chart](FM-ADSRchart.png)
diff --git a/doc/4-instrument/fm-opn.md b/doc/4-instrument/fm-opn.md
index d6365e64a..9dc2cd77d 100644
--- a/doc/4-instrument/fm-opn.md
+++ b/doc/4-instrument/fm-opn.md
@@ -37,7 +37,7 @@ These apply to each operator:
 - **Decay Rate (DR)**: Determines the diminishing time for the sound. The higher the value, the shorter the decay. It's the initial amplitude decay rate (0 to 31).
 - **Sustain Level (SL)**: Determines the point at which the sound ceases to decay and changes to a sound having a constant level. The sustain level is expressed as a fraction of the maximum level (0 to 15).
 - **Decay Rate 2 (D2R) / Sustain Rate (SR)**: Determines the diminishing time for the sound. The higher the value, the shorter the decay. This is the long "tail" of the sound that continues as long as the key is depressed (0 to 31).
-- **Release Rate (RR)**: Determines the rate at which the sound disappears after KEY-OFF. The higher the value, the shorter the release (0 to 15).
+- **Release Rate (RR)**: Determines the rate at which the sound disappears after note off. The higher the value, the shorter the release (0 to 15).
 - **Total Level (TL)**: Represents the envelope’s highest amplitude, with 0 being the largest and 127 (decimal) the smallest. A change of one unit is about 0.75 dB.
 - **Hardware Envelope Generator (SSG-EG)**: Executes the built-in envelope, inherited from AY-3-8910 PSG. Speed of execution is controlled via Decay Rate.
 
diff --git a/doc/4-instrument/fm-opz.md b/doc/4-instrument/fm-opz.md
index 10b2a5140..85439dd7e 100644
--- a/doc/4-instrument/fm-opz.md
+++ b/doc/4-instrument/fm-opz.md
@@ -37,7 +37,7 @@ These apply to each operator:
 - **Decay Rate (DR)**: Determines the diminishing time for the sound. The higher the value, the shorter the decay. It's the initial amplitude decay rate (0 to 31).
 - **Sustain Level (SL)**: Determines the point at which the sound ceases to decay and changes to a sound having a constant level. The sustain level is expressed as a fraction of the maximum level (0 to 15).
 - **Decay Rate 2 (D2R) / Sustain Rate (SR)**: Determines the diminishing time for the sound. The higher the value, the shorter the decay. This is the long "tail" of the sound that continues as long as the key is depressed (0 to 31).
-- **Release Rate (RR)**: Determines the rate at which the sound disappears after KEY-OFF. The higher the value, the shorter the release (0 to 15).
+- **Release Rate (RR)**: Determines the rate at which the sound disappears after note off. The higher the value, the shorter the release (0 to 15).
 - **Total Level (TL)**: Represents the envelope’s highest amplitude, with 0 being the largest and 127 (decimal) the smallest. A change of one unit is about 0.75 dB.
 
 ![FM ADSR chart](FM-ADSRchart.png)