diff --git a/doc/4-instrument/fm-opl.md b/doc/4-instrument/fm-opl.md
index 5449f838c..59899e4d7 100644
--- a/doc/4-instrument/fm-opl.md
+++ b/doc/4-instrument/fm-opl.md
@@ -34,7 +34,7 @@ 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 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 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.
+- **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.
 
 ![FM ADSR chart](FM-ADSRchart.png)
diff --git a/doc/4-instrument/fm-opll.md b/doc/4-instrument/fm-opll.md
index 4a1973ad6..f7cbcdd11 100644
--- a/doc/4-instrument/fm-opll.md
+++ b/doc/4-instrument/fm-opll.md
@@ -36,7 +36,7 @@ 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 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 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.
+- **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 b6203d3dd..5f75a4b0f 100644
--- a/doc/4-instrument/fm-opm.md
+++ b/doc/4-instrument/fm-opm.md
@@ -36,7 +36,7 @@ these apply to each operator:
 - **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 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.
+- **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 ed260c21e..4079773fa 100644
--- a/doc/4-instrument/fm-opn.md
+++ b/doc/4-instrument/fm-opn.md
@@ -38,7 +38,7 @@ these apply to each operator:
 - **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 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.
+- **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.
 
 ![FM ADSR chart](FM-ADSRchart.png)
diff --git a/doc/4-instrument/fm-opz.md b/doc/4-instrument/fm-opz.md
index 46edffda2..fe346278a 100644
--- a/doc/4-instrument/fm-opz.md
+++ b/doc/4-instrument/fm-opz.md
@@ -38,7 +38,7 @@ these apply to each operator:
 - **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 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.
+- **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)