5. Parameter Reference
5.2. OSC1/OSC2
The oscillator sections generate waveforms.
Exciton has two oscillators. Most functions are identical for OSC1 and 2. Both oscillators also have their own extra features. OSC1 has an oscillator sync. OSC2 has a FM parameter.
5.2.1. Wave/Quality
Specifies the waveform and its sound quality.
(1) Wave
Selects the waveform. Four waveforms (sine, triangle, sawtooth and pulse) are available.
Waveform selection is important for making synthesizer sounds. The crucial point (more than the waveform itself) is the harmonic distribution. If the waveform have contains higher harmonics, the sound get brighter. The waveforms(left) and their harmonic distributions(right) are shown below.
Sine Wave
Is the most elemental waveform. It has the only one frequency (keynote) and has no harmonics.
Triangle Wave
Has a triangular shape. It sounds like a sine wave, but has slight odd harmonics.
Sawtooth Wave
Sawtooth wave has both odd and even harmonics. Wide variety of sounds can be created with modifying its harmonic distribution with the filter.
Pulse Wave
Pulse wave also has many harmonics. There is one remarkable point of the pulse wave. The harmonic distribution can be adjusted by changing the pulse width. For 50%, the wave has only the odd components. Setting the width thinner, even harmonics appear and odd harmonics are also become larger.
(2) Quality
Sets the sound quality of the waveform. Low(L), Middle(M) and High(H) are available.
New-designed noise reduction algorithms are used in MID/HIGH oscillators in order to eliminate the alias noise with the digital processes.
Alias noise is a specific phenomenon for digital signal processing. For harmonic waveforms, the amount of alias noise depends on the base frequency. The relation with frequencies and alias noise amount is shown in below figure (left). As you see the figure, alias noise is almost negligible for low frequencies. But it generates a lot of noise for high frequencies. Exciton uses special signal processes and reduce alias noise.
Using high quality oscillators, alias noise is reduced below the audible level for all frequencies. They have the highest quiality for sounds but consume a little more CPU resource than others.
Middle quality oscillators are designed with the practical trade off between alias noise reduction and CPU consumption. You can use middle quality oscillators for most cases. Especially, using a sustain pedal consumes many voices and high quality oscillators may not be appropriate (unless you are using a high-end machine). Using middle quality oscillators, you can play sounds with a sustain pedal on even an entry-model computer.
Low quality oscillators do nothing for alias noise. You might think these oscillators are no use at all. But as long as using them for base tones, it makes no actual deference from middle/high quality oscillators. Furthermore, there is one interesting usage for these oscillators. Setting waveform to sawtooth (or pulse) and pitch to the highest, it generates a radical noise. It can be used for sound effects, percussions or anything you like.
On the other hand, because sine waves have no harmonics, they generate no alias noise. Low and middle quality oscillators have enough quality for almost all cases (middle quality is slightly better, but actually no audible difference).
High quality sine oscillator is extraordinary pure. Its S/N ratio is nearly 120dB. It can be even used for technical precision measurements (but low and middle are enough for music).
5.2.2. SYNC (OSC1 only)
Specifies a oscillator phase synchronization from OSC2 to OSC1.
When SYNC is set to ON, OSC1's wave is forced to reset at the every timing when OSC'2 phase comes to zero. As a result, OSC1's base frequency is locked to the OSC2's pitch. It comes to the complex waveform depends on frequency (pitch) of both OSC1 and OSC2.
A typical application of using oscillator sync is as follows.
When SYNC is set to ON, OSC1's base frequency is locked to that of OSC2. You can set the base pitch by setting OSC2's pitch.
Next, if you set OSC1's pitch higher than OSC2 and modulate OSC's pitch with envelopes or LFO's, you can obtain complex modulation sounds that depends on the modulation.
5.2.3. FM (OSC2 only)
Sets an FM depth of OSC2.
FM (frequency modulation) is a kind of audio modulation that modulates an oscillator's frequency with another oscillator. OSC2 has this function. OSC2's frequency is modulated with OSC1 output with setting FM amount.
With emphasizing FM depth, the waveform of OSC1 is modified with OSC2. It results to make new harmonic components which do not exist on the original waveform.
The new harmonics which are generated with FM also has alias noise component. Even if you use a high quality oscillator, it cannot be eliminated from the waveform. You can use a filter to get rid of unneeded noise components.
In fact, Exciton's "FM" is not a strict frequency modulation. It uses a phase modulation, which is a similar effect to FM.
There are some (historical) reasons to use the word "FM" for phase modulation. Frequency modulation and phase modulation are similar effects. Because FM modulates a phase via frequency, they result to the similar sound character. As for the signal processing, phase modulation is slightly efficient. By this reason, most synthesizers that have "FM" function (like YAMAHA DX7) are actually using phase modulation.
5.2.4. PulseWidth
Sets the width of the pulse wave. The function is active when the pulse is selected as the waveform. It does nothig if another waveform is selected.
The pulse width can be set from 0 to 100%. Setting to 50% specifies the square wave and setting forward or backward makes the pulse thinner. Setting to 0% or 100% makes width to 0 and makes the output to silent (this is a specification, not a bug).
Relation with wave shapes and widths are shown below.
Changing pulse width, the wave shifts vertically and cancels DC offset to zero.
5.2.5. Pitch
Sets the oscillator's coarse frequency pitch.
This specifies the oscillator frequency pitch. The pitch can be set from -48(-4 Octaves) to +48(+4 Octaves) by semitones.
5.2.6. Detune
Sets the oscillator's fine frequency pitch (detune).
The fine pitch can be set from -100cent(-1 semitone) to +100cent(+1 semitone).
5.2.7. Key Follow
Specifies the oscillator's key follow ratio versus MIDI note-on messages.
Key follow ratio can be set from 0% to 200%. 100% sets the pitch scale to the normal keyboard (a semitone). 200% comes to the whole tone (2 semitones) and 50% to the quatertone. Setting to 0% comes to the same pitch for all notes and the pitch is specified only by Pitch and Detune.
5.2.8. Modulation Source/Destination A/B
Specifies modulation source/destination configurations.
Each oscillators have two modulation slots (A/B). Exciton has 4 modulation sources (2 envelopes and 2 LFO's) and two of them can be selected and assigned to the oscillator pitch. If the pulse wave is used, they can be also assigned to the pulse width.
(1) Source
Specifies a modulation sourtce. It can be selected from ENV1, ENV2, LFO1 and LFO2.
(2) Destination
Specifies the modulation destinations.
Clicking FREQ button on, the modulation is added to the oscillator pitch. Clicking PWM button on, the modulation is added to the pulse with (no effect for other waveforms). Both switches can be set to on at the same time.
OSC2 also has FM button. Clicking FM button on, the modulation is added to the FM amount.
5.2.9. Modulation Depth A/B
Sets the modulation depth.
The depth can be set to both positive and negative directions. If you assign a envelope to the oscillator pitch, setting to the positive becomes the pitch up and the negative becomes the pitch down.
The knob scale for the modulation depth is quadratic (not linear). It is gentle around zero and gets steeper with both directions. You can set both the fine detune and the large sweep with one knob.
If you want to set a large modulation and 100% is not enough, you can specify the same setting for both modulation A and B. It makes the modulation twice bigger than one. Furthermore, you can add wide variety of extra modulation routings with assignable modulation.
5.2.10. Modulation Velocity Sens. A/B
Sets the MIDI note on velocity sensibility with the modulation depth.
Setting the sensitivity to 100%, the depth varies from 0 to 200% with the note on velocity. Setting to 0% makes the constant for all velocities.
You can set the velocity sensitivity for the modulations and add expressions to the sounds. For example, adding the pitch change with the envelope to the beginning of the note is a common technique for the brass sounds. Using the velocity sens, the expression with variable pitch change for the velocity is added to the sound.
