Merge branch 'freq-mod-docs2' of https://github.com/freq-mod/furnace into freq-mod-freq-mod-docs2

papers/doc/7-systems/opll.md

@@ -2,6 +2,11 @@
 
 the YM2413, otherwise known as OPLL, is a cost-reduced FM synthesis sound chip, based on the Yamaha YM3812 (OPL2). thought OPL was downgraded enough? :p
 
+OPLL spawned also a few derivative chips, the best known of these is:
+- the myth. the legend. THE VRC7. 6 channels, *rather interesting* instruments sound bank, no drums mode
+- Yamaha YM2423, same chip as YM2413, just a different patch set
+- Yamaha YMF281, ditto 
+
 # technical specifications
 
 the YM2413 is equipped with the following features:

papers/doc/7-systems/saa1099.md

@@ -1,6 +1,9 @@
 # Philips SAA1099
 
-this was used by the Game Blaster and SAM Coupé. it's pretty similar to the AY-3-8910, but has stereo sound, twice the channels and two envelopes, both of which are highly flexible.
+this was used by the Game Blaster and SAM Coupé. it's pretty similar to the AY-3-8910, but has stereo sound, twice the channels and two envelopes, both of which are highly flexible. The envelopes work like this:
+
+an instrument with envelope settings is placed on channel 2 or channel 5
+an instrument that is used as an "envelope output", is placed on channel 3 or channel 6. You may want to disable wave output on the output channel.
 
 # effects
 

papers/doc/7-systems/vrc6.md

@@ -5,6 +5,8 @@ the most popular expansion chip to the NES' sound system.
 the chip has 2 pulse wave channels and one sawtooth channel.
 volume register is 4 bit for pulse wave and 6 bit for sawtooth, but sawtooth output is corrupted when volume register value is too high. because this register is actually an 8 bit accumulator, its output may wrap around.
 
+For that reason, the sawtooth channel has it's own instrument type. Setting volume macro and pattern editor volume setting too high (above 42/2A) will distort the waveform.
+
 pulse wave duty cycle is 8-level. it can be ignored and it has potential for DAC at this case: volume register in this mode is DAC output and it can be PCM playback through this mode.
 Furnace supports this routine for PCM playback, but it consumes a lot of CPU time in real hardware (even if conjunction with VRC6's integrated IRQ timer).
 

papers/doc/effects.md

@@ -0,0 +1,66 @@
+# effect list
+
+most of the effect numbers are from ProTracker/FastTracker 2.
+however, effects are continuous, which means you only need to type it once and then stop it with an effect value of `00`.
+
+- `00xy`: arpeggio. after using this effect the channel will rapidly switch between `note`, `note+x` and `note+y`.
+- `01xx`: slide up.
+- `02xx`: slide down.
+- `03xx`: note portamento.
+  - a note must be present for this effect to work.
+- `04xy`: vibrato. `x` is the speed, while `y` is the depth.
+  - maximum vibrato depth is ±1 semitone.
+- `07xy`: tremolo. `x` is the speed, while `y` is the depth.
+  - maximum tremolo depth is -60 volume steps.
+- `08xy`: set panning. `x` is the left channel and `y` is the right one.
+  - not all systems support this effect.
+- `09xx`: set speed 1.
+- `0Axy`: volume slide.
+  - if `x` is 0 then this is a slide down.
+  - if `y` is 0 then this is a slide up.
+- `0Bxx`: jump to pattern.
+- `0Cxx`: retrigger note every `xx` ticks.
+  - this effect is not continuous.
+- `0Dxx`: jump to next pattern.
+- `0Fxx`: set speed 2.
+
+- `9xxx`: set sample position to `xxx`\*0x100.
+  - not all systems support this effect.
+
+- `Cxxx`: change song Hz.
+  - `xxx` may be from `000` to `3ff`.
+
+- `E0xx`: set arpeggio tick.
+  - this sets the number of ticks between arpeggio values.
+- `E1xy`: note slide up. `x` is the speed, while `y` is how many semitones to slide up.
+- `E2xy`: note slide down. `x` is the speed, while `y` is how many semitones to slide down.
+- `E3xx`: set vibrato direction. `xx` may be one of the following:
+  - `00`: up and down.
+  - `01`: up only.
+  - `02`: down only.
+- `E4xx`: set vibrato range in 1/16th of a semitone.
+- `E5xx`: set pitch. `80` is 0 cents.
+  - range is ±1 semitone.
+- `EAxx`: toggle legato.
+- `EBxx`: set sample bank.
+  - does not apply on Amiga.
+- `ECxx`: note off after `xx` ticks.
+- `EDxx`: delay note by `xx` ticks.
+- `EExx`: send external command.
+  - this effect is currently incomplete.
+- `EFxx`: add or subtract global pitch.
+  - this effect is rather weird. use with caution.
+  - `80` is center.
+- `F0xx`: change song Hz by BPM value.
+- `F1xx`: single tick slide up.
+- `F2xx`: single tick slide down.
+- `F3xx`: fine volume slide up (64x slower than `0Axy`).
+- `F4xx`: fine volume slide down (64x slower than `0Axy`).
+- `F8xx`: single tick volume slide up.
+- `F9xx`: single tick volume slide down.
+- `FAxy`: fast volume slide (4x faster than `0Axy`).
+  - if `x` is 0 then this is a slide down.
+  - if `y` is 0 then this is a slide up.
+- `FFxx`: end of song/stop playback.
+
+additionally each system has its own effects. [click here for more details](../7-systems/README.md).