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+# OPLL FM synthesis instrument editor
+
+The OPLL FM editor is divided into 5 tabs:
+
+- **FM**: for controlling the basic parameters of FM sound source.
+- **Macros (FM)**: for macros controlling algorithm, waveform and feedback
+- **Macros (OP1)**: for macros controlling FM parameters of operator 1
+- **Macros (OP2)**: for macros controlling FM parameters of operator 2
+- **Macros**: for miscellaneous macros controlling volume, arpeggio, and preset.
+
+## FM
+
+The OPLL synthesizer is two-operator, meaning it takes two oscillators to produce a single sound.
+
+These apply to the instrument as a whole:
+- **Feedback (FB)**: Determines how many times operator 1 returns its output to itself. (0-7 range)
+- **Sustain (SUS)**: enables the sustain flag (sets the release rate to 5) 
+- **DC (half-sine carrier)**: Sets the waveform produced by carrier operator to half-sine
+- **DM (half-sine modulator)**: Sets the waveform produced by modulator operator to half-sine
+
+To the right, there is a drop down menu for OPLL preset instrument selection.
+
+These apply to each operator:
+- The crossed-arrows button can be dragged to rearrange operators.
+- The **OP1**, **OP2** buttons enable or disable those operators.
+- **Amplitude Modulation (AM)**: Makes the operator affected by LFO tremolo.
+- **Envelope generator sustain flag (EGS)**: When enabled, value of Sustain Level is in effect.
+- **Attack Rate (AR)**: determines the rising time for the sound. The bigger the value, the faster the attack. (0-15 range)
+- **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. (0-15 range)
+- **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. (0-15 range)
+- **Release Rate (RR)**: Determines the rate at which the sound disappears after KEY-OFF. The higher the value, the shorter the release. (0-15 range)
+- **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.
+
+![FM ADSR chart](FM-ADSRchart.png)
+
+- **Envelope Scale (KSR)**: Also known as "Key Scale". Determines the degree to which the envelope execution speed increases according to the pitch.
+- **Frequency Multiplier (MULT)**: Determines the operator frequency in relation to the pitch. (0-10, 12, 15 range)
+- **Pitch Modulation (VIB)**: Makes the operator affected by LFO vibrato.
+
+## macros
+
+Macros define the sequence of values passed to the given parameter. Via macro, along with the previously mentioned parameters, the following can be controlled:
+
+## FM Macros
+
+All parameters are listed above.
+
+## OP1-OP4 Macros
+
+All parameters are listed above.
+
+## Macros
+
+- **Arpeggio**: Pitch change sequence in semitones.
+- **Patch**: changes the playing preset mid-note
+- **Pitch**: fine pitch.
+  - **Relative**: pitch changes are relative to the current pitch, not the note's base pitch.
+- **Phase Reset**: Restarts all operators and resets the waveform to its start. Effectively the same as a `0Cxx` retrigger.
+
+
+# links
+
+[FM instrument tutorial](https://www.youtube.com/watch?v=wS8edjurjDw): A great starting point to learn how create and work with FM sounds. This was made for DefleMask, but all the same principles apply.