New features (#21)

* add new parameters in addsynth

* add new filter types

* add more descriptions to ADDsynth

* update sreenshots

* fix FilterModule

* add moog and comb filter screenshots

* add more details for moog and comb filter

* add signal flow for addsynth voice

* Add some missing text in modulation section and

---------

Co-authored-by: Friedolino <[email protected]>

ADDsynth.adoc

@@ -38,9 +38,12 @@ image::imgs/lfo.png[]
 - *Start:* LFO Start Phase - If this knob is at the lowest value, the LFO Start Phase will be random.
 - *Str.:* LFO Stretch
 - *Delay:* LFO Delay
+- *LP:* Cutoff frequency of the lowpass filter applied to the lfo output. (i.e. how much the output is smoothed) 
+- *F.In:* Time it takes to fade in the lfo amplitude up to depth after the delay time 
+- *F.Out:* Time it takes to fade the amplitude out after key release.
 - *A.R.:* LFO Amplitude Randomness
 - *F.R.:* LFO Frequency Randomness
-- *Sync:* ???
+- *Sync:* If this option enabled the LFO oscillates in the same phase for all notes (given the LFO frequency is the same)
 
 ==== Filters
 Zyn-Fusion offers several different types of filters, which can be used to shape the spectrum of a signal. The primary parameters that affect the characteristics of the filter are the cutoff, resonance, filter stages, and the filter type.
@@ -49,14 +52,14 @@ Zyn-Fusion offers several different types of filters, which can be used to shape
 - *Resonance:* The resonance of a filter determines how much excess energy is present at the cutoff frequency. In Zyn-Fusion, this is represented by the Q-factor, which is defined to be the cutoff frequency divided by the bandwidth. In other words higher Q values result in a much more narrow resonant spike.
 - *Stages:* The number of stages in a given filter describes how sharply it is able to make changes in the frequency response.
 
-====== General
+===== General
 image::imgs/filter-analog.png[]
 
 - *Cutoff:* Cutoff frequency.
 - *Q:* Level of resonance for the filter.
 - *F.Track:* Frequency tracking amount. When this parameter is positive, higher note frequencies shift the filter’s cutoff frequency higher.
-- *Scale:* ???
-- *Sense:* Velocity sensing. (100% to the right to disable).
+- *Scale:* Velocity sensing amount 
+- *Sense:* Velocity sensing shape. with higher values the sensivity is shifted towards low velocities
 - *Stages:* Filter stages.
 - *Class:* Category of synth.
 - *Type:* Type of filter to use.
@@ -75,6 +78,8 @@ The Envelopes share the same basic parameters:
 - *Decay:* The volume drops from the maximum value to a level called "Sustain level"
 - *Stretch:* How the envelope is stretched according to the note. On the higher notes the envelopes are shorter than lower notes.
 - *Forced release:* If this option is turned on the release will go to the final value, even if the sustain stage is not reached.
+- *Repeat:* If this option is active the envelope is started again when reaching release
+
 
 ===== Amplitude Envelopes
 Amplitude envelopes control the amplitude of the sound.
@@ -155,6 +160,7 @@ image::imgs/add-synth-voice-amplitude-general.png[]
 - *Pan:* Panning. (100% to the left is random).
 - *Delay:* delay before the voice starts.
 - *Bypass GL Filter:* If the voice signal bypasses the global filter.
+- *F. Ctl Bypass:* If the voices filter is not affected by cutoff midi CC
 - *RESON:* Enable/Disable the resonance of the voice.
 
 ===== Frequency
@@ -175,17 +181,62 @@ This is your oscillator and modulator-oscillator. Full documentation link:Oscill
 
 ==== modulation
 
-===== Amplitude
-image::imgs/add-synth-modulation-amplitude.png[]
+image::imgs/add-synth-modulation-none.png[]
+
+
+===== Mix
+Mix is actually not a modulation type but something like wave morphing or one dimension of a vector synthesis.
+The modulation amount set with the "Vol." knob and the Amp envelope represents the mixing ratio between "modulator" and "carrier" oscillator.
+
+
+===== Ring
+Ring modulation was used in the Roland D50 but also in many classic analog synthesizers for example from Oberheim.
+The values of modulator and carrier are simply multiplied.
+Used with sine oscillators for both modulator and carrier that adds the sum and the difference of their frequencies to the spectrum.
+It can be used to create inharmonics for metallic or bell like sounds.
+
+
+===== Phase
+The value of the modulator is applied as phase offset. That's what Yamaha called FM in the famous DX7.
+By modulating the phase angle of the oscillator, phase modulation alters the frequency content of the sound, 
+allowing for the creation of complex, evolving timbres and textures.
+
+
+
+===== FM
+The value of the modulator is applied as frequency offset. 
+[WARNING]
+Aliasing
+====
+Because of the wide applicable range it is nearly impossible to prevent aliasing at high FM amounts.
+====
+
+
+===== PWM
+An enhancement of phase modulation with pairs om mirrored modulators
 
-===== Frequency
-image::imgs/add-synth-modulation-frequency.png[]
 
 ==== voice list
 image::imgs/add-synth-voice-list.png[]
 
+The AA button enables the anti aliasing sampling filter. Can be useful when using high range frequency LFOs or FM.
+
 ==== resonance
 image::imgs/add-synth-resonance.png[]
 
+The resonance is a spectral modification of the oscillator that is applied "offline" while constructing the waveform.
+
+[WARNING] 
+Resonance in frequency modulated Oscilators
+==== 
+When the frequency is modulated the resonance spectrum is shifted, too.
+====
+
+
+In the plot the spectral fingerprint can be drawn by hand or generated by random generators with fine, medium or large granularity.
+The curve can also be smoothed. The resulting diagram can be shifted or scaled with respect to the full spectrum.
+
+=== signal routing diagram
+image::imgs/flow_add_voice.png[]
 
-* [TODO] signal routing diagram
+The diagram shows a simplified signal routing for a single voice.

FilterModule.adoc

@@ -8,6 +8,8 @@ State variable filters:: Limited filter types, but good under heavy modulation
 Analog filters:: Standard Biquad formulations for a variety of shapes
 Formant filters:: Good for modeling speech spectral shapes. Composed by many
 sub-filters.
+Moog filters:: Good for a warmer feeling - especially with some gain
+Comb filters:: Good for string like effects or intense spectral and phase effects
 
 ===== Analog Filters
 
@@ -44,3 +46,46 @@ harmonic profile of your sounds and make it evolve over time.
 More on that later in this chapter.
 
 image::imgs/20180413-144131.png[]
+
+===== Moog Filter
+
+image::imgs/filter-moog.png[]
+
+The Moog filter type is an attempt to emulate the renowned transistor or diode ladder filter found in Moog and other classic analog synthesizers. 
+It employs the Zero Delay Feedback (ZDF) approach to ensure a level of accuracy in replicating the filter's behavior. 
+
+LP:: low pass
+HP:: high pass
+BP:: Bandpass
+
+===== Comb Filter
+
+image::imgs/filter-comb.png[]
+
+The Comb Filter operates as a tunable delay line, introducing a series of notches and peaks 
+in the frequency spectrum due to the interaction between the original signal and its delayed version. 
+The term "comb" aptly depicts the spectral pattern resembling the teeth of a comb, 
+showcasing the alternating constructive and destructive interference patterns. 
+
+This filter is commonly used to simulate various acoustic effects, such as reflections, 
+chorus-like sounds, or enhancing the perception of spaciousness in audio signals.
+
+BWD:: adds a delayed version of the output signal. the feedback structure leads to heavy resonance
+FWD:: adds a delayed version of the input signal. the feed forward structure leads to more subtle phase effects
+both:: combination of BWD and FWD. heavy resonances are dominant 
+BWDN:: subtracts a delayed version of the output signal. similar to BWD. can be used for example to remove even harmonics
+FWDN:: Subtracts a delayed input signal, emphasizing frequency cancellation for targeted harmonic removal or notching in the spectrum.
+bothN:: Utilizes subtraction from both input and output signals
+
+[NOTE]
+
+Poor Mans Physical Modelling
+======
+The comb filter can be used as a string like oscillator. 
+To accomplish that apply it as voice filter to a burst of noise. 
+But make sure the amplitude envelope doesn't go too fast to zero as that would turn off the voice.
+If F.Track is 100% it's frequencies are proportional to the pitch.
+To keep in tune you may set Scale to 0 (no velocity impact) 
+and enable "F. Ctl Bypass" in the voices Amplitude General Settings (no midi cc impact)
+======
+