This is part two of my exploration of the Andromeda A6 synthesizer.
It's
a wonderful synthesizer, which I never tire of.
Endless new sounds ... I discover things every day.
The
official manual is really long (as you'd expect) from such a complex
synth, so this is my attempt to break things down, into smaller parts
for myself and others . If this helps someone else, that great too.
Do let me know if there are any errors or omissions. I'll correct them as soon as I can.
I'll constantly add to these posts as I discover more about this wonderful instrument.
Part 1 & 2 are here:
Alesis decided to base the Andromeda's oscillators on the Moog 921b.
The Oscillators have been shrunk into eight ASO chips - the ASO. (application specific oscillator).
In total, there are 32 oscillators (two per voice) with sub-oscillators plus hard and soft sync.
Each Voice also offers noise (in white, pink and red varieties) and a ring modulator.
There are 16 ring modulators (one per Voice).
Oscillators
Each has Sqr, Saw, Tri & Sine waves.
All 4 waves can be on simultaneously .
Selecting a waveform is as simple as pressing the button next to its panel label.
The Saw waveform has both +ve & -ve polarity.
Note, that if you have two SAW waves of the same frequency and opposite polarity, they will cancel each other.
Only the Pulse wave has a pulse width knob for each oscillator.
It also has a level control.
Each oscillator has tuning knobs for coarse, fine and ultra-fine tuning control. These
three controls have their neutral positions (where A-440 or Standard Pitch is
achieved) at 12 o’clock.
The OCT LED will light at each octave interval
You can only sync osc 2 to Osc1.
(the button for this is where they join on thepanel).
You can see it's control on the OSC2 display page.
Oscillator SYNC
Normally, the two VCOs are free runnnig.
But we can sync their cycles.
There are two types of sync
Hard sync will lock phase with fundamental frequencies.
Soft sync will lock phase with harmonic frequencies.
Touching the View button in either osc will display its settings on the screen.
VCO MODULATION
The VCOs can be modulated in a number of ways.
1. ENV 1 AMOUNT
2. OSC 2 FM
3. NZEXT
ENV 1 AMOUNT
Modulating the VCOs is really impt.
Each oscillator has several pre-routed and three custom
modulations.OSC 1 is pre routed to OSC2 for modulation
(FM synthesis) .. amt is controlled by the modulation pot.
OSC2 is pre routed to itself & OSC1 for modulation
(FM synthesis) ... separately & together.
amt is controlled by the modulation pot (ENV 1 AMOUNT). Keep in mind that negative values invert the
action of the selected source.
This is the ENV 1 AMOUNT page:
ENV1 can be configured to effect the pitch of both oscillators .
This page is shared by both oscillators.
There are 4 ways to access this page:
a) OSC 1 menu
b) OSC 2 Menu
c) the ENV 1 knob
d) The ENV 1 button
OSC 2 FM
As discussed earlier, The frequency of OSC 1 can be modulated by OSC 2, hence the term “OSC 2 FM”, or
“frequency modulation by Oscillator 2”.
Because of this, the OSC2 FM page is only accessible by pressing the OSC 1 view button.
Quote:
"a VCO oscillates at a rate that puts its frequency in the
audible range, as opposed to an LFO which typically oscillates at a slower rate that is
below the range of pitched audio. Since a VCO can cover the entire audible
frequency range (and then some: 20Hz to 22Khz), its effect as a modulation source
for another oscillator is much different than of an LFO."
" When you modulate a VCO by another VCO, the modulation rate is high enough to
produce an entirely new set of harmonics called sidebands. The result of this type of
modulation is often described as “buzzing” or “metallic”. Also significant in the
modulating process is VCO tracking by the keyboard. When tracked by the
keyboard, the frequency of the source VCO changes with each new key played,
changing the characteristics of the sound". (A6 Manual)
The ratio between the frequencies of the modulation oscillator (Modulator) & target oscillator (carrier) are impt.
There are two types of oscillator-generated FM in the A6, linear and exponential.
OSC
1 features both linear and exponential FM, OSC 2 features exponential FM only.
Linear = No pitch change will occur except at extreme values. No harmonics are added.
Exponential = pitch changes occur. Thus harmonics are added when you shift the pitch of the note.
(Exponential is how most synths like the DX7 do FM)
Note that the FM output doesn't pass through the Pre-Filter Mixer.
On this page you will also see PWM - Pulse width modulation (see below)
Filters (specifically their frequency) can also be modulated by the oscillators.(see the filter section).
NZEXT
The NZEXT page is a common page shared between OSC 1 & OSC 2
These can be used for modulation of the VCOs
There are 3 types of noise :
White (high frequency), Pink (mid frequency) & red (low
frequency) .
Plus there is OSC 1.
---------------------------------------------------------------------
Custom Modulation Inputs
Each VCO has three custom
modulation inputs.
A lighted LED adjacent to a MOD button indicates that a
custom mod has been created for that VCO. Pressing a mod button shows its current
modulation route in the display (if any) and displays the parameters that will allow
you to create a custom modulation route.
You can access these three MODs at once, as well as PWM and FM.
Pressing the MODS (soft button 8) button displays a summary table of the current modulation routes for the currently selected VCO.
Reading from left to right, the table lists the
modulation’s name, the source, the amount, the offset and the destination. Soft buttons 3, 4 and 5 correspond to the MOD 1, MOD 2 and
MOD 3 buttons in the VCO sections and display their respective pages when pressed.
Soft button 6 PWMOD corresponds to the PWM buttons in the VCO sections and soft
button 7 FMMOD corresponds to the MOD button on the OSC 2 FM knob on OSC 1.
Pulse Width Modulation.
PWMOD/PWM
Both VCOs provide for PWM
Thus the width of the pulse wave which is set by the PULSE WIDTH
knob can be modulated with an external source.This is useful for making sounds ranging from lush string
ensembles to thick synth pads.
You can use a LFO, an envelope, the keyboard (velocity,
aftertouch or key track), the pitch bend , modulation wheels, pedals or the ribbon
controller.
Prefilter Mix
This mixer allows great flexibility in combining sounds in a multitude of ways.
The PRE FILTER MIX controls the A6’s sound sources going into the filters.
4 knobs concern the two OSC and their 2 suboscillators.
1 knob concerns the Ring Mod
1 Knob concerns Noise & external inputs.
The level of each of these inputs can be modulated. Each has it's own MOD button.
Press the MOD buttons to access these settings.
Thus this module allows you to mix the relative output levels of the VCOs (and add in their sub-oscillators if
desired), select and mix in a noise source or external audio (but not both), mix in
Filter Feedback, and set the level of the Ring Modulator. All of these sound elements
can be mixed into a Program at the same time.
The Ring Modulator is especially interesting in that you can route it into the Filters as
above, bypass the Filters altogether (it has a direct route into POST FILTER MIX) or have
both the Filtered and unfiltered signals at once.
The Ring Modulator takes the waveforms of the two VCOs and multiplies them by each other.
The
result is a new waveform that is composed of two
frequencies: the sum of the two original waveforms’
frequencies and the difference of their frequencies
Experiment with different VCO frequencies, and different waveforms.
Remember that sine waves have no harmonics. In comparison, square & saw waves are harmonic rich.
Filter Feedback
Filter feedback is a popular "trick" of many synths.
You plug the output of your headphone jack into the filter input.
This overloads the filter & gives a gritty,
nasty sound
You can do this on the A6.
Press the
FILTER FEEDBACK button to enable this function and use the NOISE EXT knob to control
the feedback level. Please note that the level settings of the Filters – FILT1 LP, FILT1 HP,
FILT1 BP and FILT2 LP – also affect the feedback. Use these five knobs in conjunction to
obtain the feedback you want.
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