Although it shares some controls with Prologue (which I looked at in SOS April 2008), Mystic is a very different beast, with a synthesis engine that's centred around comb filtering and capable of producing some really interesting sounds. The Plug-In Reference PDF does its usual efficient job and describes Mystic's key controls, but it is less useful as a guide to the synth's architecture or as a programming tutorial, so...
I'll start with the basics. Sounds in Mystic are created in two main stages. The first involves the configuration of an 'impulse sound', which is fed into Mystic's three comb filters. The creation of the impulse sound is controlled using the topmost section of Mystic's interface, and the description of this stage in the Plug-In Reference is, I'm afraid, rather confusing. It tells you that the "Impulse Control section has two basic waveforms that are filtered through separate spectrum filters". While the two spectrum filters (labelled A and B) are present and correct and they can both be configured by the user (see the 'Bugs In Boxes' panel elsewhere in this article), only one Waveform menu is present, and this selects the waveform (from a choice of six types) to be sent through spectrum filter A. It isn't immediately obvious, but some comparative tests between the two waveforms leads me to believe that the waveform sent to spectrum filter B is fixed as a sawtooth (which would explain why there's no need for a second Waveform pop-up box to be provided).
The two spectrum filters offer a selection of preset contours, but you can also draw your own using the mouse. In normal use, setting a frequency contour in one display will configure an inverse contour in the other, but holding down Shift while drawing with the mouse allows the two filters to be configured independently. The shape of the contour dictates which frequencies are cut or boosted, and the effect of this can be heard clearly via a patch such as that shown in the screenshot above. Here, all the LFO, ENV, Event and EFX options have been turned off, and the comb filter has been removed by setting the feedback control to zero. In this configuration, and with a suitable ADSR envelope configured for Env 2 (by default, this is the envelope that is applied to the output of the Impulse Control stage), the influence of the spectrum filters on the impulse sound can be examined. The 'Multiband' spectrum preset provides a good way to demonstrate this, because it contains a series of extreme peaks and troughs. Setting the Morph control to either 0 or 100 (so that you only hear one or other of the spectrum filters operating) and then simply playing a series of notes up or down the keyboard allows you to hear where these notches or peaks are, as the frequency content of the sound will change.
The four other controls in the Impulse Control section (Coarse, Cut, Morph and Raster) are fairly straightforward. Coarse offsets the pitch of the impulse sound (+/-4 octaves), while Cut acts rather like a standard high-cut filter, with lower settings reducing the high-frequency content. As I implied above, the Morph control adjusts the balance between the output of the two spectrum filters. Finally, the Raster control is used to remove harmonics from the impulse sound. As with the Cut control, lower values tend to produce a darker sound, although the effect is somewhat different.
The impulse sound is then passed to the second stage of the Mystic engine — the comb filters. As can be seen on the first screenshot, an envelope (the default is Envelope 2) and a Level setting are applied to the impulse sound prior to it being fed to the these filters. If the envelope includes significant decay, sustain and release times, the character of the impulse sound has a stronger influence on the timbre of the final output. However, for some presets the impulse sound is just an impulse, with very short decay and no sustain or release elements. With this sort of envelope shape, the detailed settings in the Impulse Control section are somewhat less significant.
The influence of this initial envelope stage can be illustrated by loading the 'Pizzicat' preset (it is worth disabling the Delay and Modulation processing in the EFX window to make the influence of the envelope more obvious). This patch uses an envelope that consists of an instant attack, a short release and zero decay and sustain times, and it produces a sort of bright, fizzy guitar tone. If you adjust the properties of Envelope 2 (in the ENV window), the change in the sound is quite dramatic, as more of the character of the impulse sound reaches the comb filters.
A number of the other controls in the comb filter section are pretty self-explanatory, so I'll be brief: the Pitch (coarse pitch) and Fine controls provide overall pitch adjustment for the synth's output; the Key Tracking switch operates in the expected fashion; and Crackle also does pretty much what it says on the tin (it adds noise to the comb filters). For any sustained sounds, unless you're going for a special effect, a little Crackle goes a long way — although the 'Granulator' preset provides a good example of what's possible.
More interesting are the Feedback, Damping and Detune controls. Feedback determines the amount of signal sent back into the comb filters for reprocessing. If set to zero (the 12 o'clock position), there's no feedback, essentially turning off the comb filter — and while this may defeat the object of using Mystic in the first place, it is useful when programming a sound from scratch, because it allows you to hear the character of the impulse sound in isolation. Both positive and negative feedback values can be set. More extreme values of both generate sounds with longer decays, while negative values create a more hollow sound (good for bell-like tones) than do positive ones — and while it is by no means universally true, Mystic's more melodic presets tend to favour positive feedback values.
The Damping control influences the low-pass filter that is applied to the sound being fed back into the comb filters. By removing the higher frequencies, it causes the sound to become gradually softer over time (each time the sound goes through the feedback loop more high-frequency content is removed). This can be used to mimic the character of many acoustic sounds, such as, for example, a plucked string, where the higher frequencies decay more quickly than the lower ones. If you want to avoid this, turning the Damping control up to 100 will switch off the low-pass filter.
The Detune control offsets the frequencies of the notches within the three comb filters, detuning them relative to each other. At low settings, this can create a gentle thickening of the sound (not unlike a chorus effect). At higher settings, this detuning can get pretty extreme (as illustrated by the 'Doppler' preset) and the output becomes more sound effect or sound design than melodic.
The output from the comb filter stage passes through a standard ADSR volume envelope (which, by default, is Envelope 1 from the ENV window). The overall Volume and Pan controls operate as expected and Portamento (with normal and legato modes) is also included.
Bugs In Boxes
On my test PC, there's something a little odd about the behaviour of the displays within the Mystic spectrum filter boxes. The contents of the displays do not always seem to correctly update themselves when I'm browsing through the presets and, for example, if I have two instances of Mystic open and both have the same preset selected, the spectrum filters sometimes show different filter curves. This behaviour can be cleared by saving, closing and then re-opening the Project, but it is a little irritating if you're trying to study how some of the presets are constructed, as you can't rely on the displays to be accurate. I've reproduced this behaviour on a second PC so I suspect it is a genuine bug, although I'm not sure whether it is also an issue for Mac users.
Mystic isn't an obvious choice for creating convincing emulations of real string-based instruments, but (as some of the presets show) it's capable of producing some interesting synthetic string-type sounds. As noted above, the 'Pizzicat' preset uses the comb filter input envelope to define a very short impulse sound, and this is typical of many of the 'plucked string' presets in Mystic that use similar forms of envelope shapes (for example, the 'Pluck One', 'Cello Two' and 'Plucked String' sounds). This makes sense, as the impulse sound is attempting to reproduce the effect of the initial striking or plucking of the string — which is a very short-lived event. Unsurprisingly, the majority of the string-style patches (including those listed above) use the String Body spectrum filter preset. However, some of the other six waveforms can be used, and the other Impulse Control settings can vary over quite a wide range and still be perfectly useable.
Many of the string-style presets share a number of other similar settings as well. Low (or zero) Damping values tend to be used, whereas Feedback values tend to be high (130+). This combination means that there's plenty of comb-filter processing, causing the sounds to lose higher-frequency harmonics quite quickly. Given that most of the string-style presets are intended to be melodic, low (or zero) values of Detune are the norm. The final common feature is the output envelope. Some examples from the presets listed above are shown in the screen shot below. The combination of fast attack, short decay and low sustain values (as used for the 'Pizzicat' and 'Pluck One' presets) emphasises the initial attack of the sound. The 'Plucked In' preset is similar but the lower sustain value means that it is more like a plucked string than a bowed one: it doesn't simulate the continuous excitation of the string that would be provided by a bow. In contrast to all of the others, the 'Cello Two' preset features a slower attack phase and slower decay, and this results in a sound that is more suitable for slower, single note, melodic lines.
Mystic excels in the creation of pad or soundscape-style sounds. Some fabulous presets illustrate this, ranging from the fairly musical 'At The Movies' (which seems to be both mellow and urgent at the same time), via the almost organ-like 'Rising Pad' and 'Trembling Pad' (quite foreboding in the lower register), to the more unsettling and abstract 'Arhythmic Chaos' or scary (and speaker damaging) 'Love No Screaming'.
When exploring pad-type presets such as those listed above, it soon becomes obvious that a wide range of settings in the Impulse Control section can be used. Indeed, any of the basic waveform types are suitable and the Randomize option for the Spectrum Filters can throw up some perfectly usable filter shapes. However, there are some controls in the comb filter stage where the settings show more similarities. Output envelope shapes (usually Envelope 1) often feature zero decay, high sustain levels (often 100) and long release times. Attacks can be short or longer (so that the sound fades slowly up to full volume when a note is played). In many cases, the comb filter input envelope (usually Envelope 2) has similar properties — very different from the string-style sounds discussed above — and this means that the tonal characteristics of the impulse sound have a stronger influence on the overall timbre. For all the presets listed above, Feedback levels are positive and in the mid- to high range. For more musical pads, Detune and Crackle values tend to be low (less than 10), but if you want to create a 'pad gone bad', slightly higher values for these two controls can soon add an unsettling feel.
However, the key element that adds interest to most pad sounds is the way in which they may change (subtly or otherwise) with time as the note is sustained, and to achieve this we need to turn to the ENV, Event and LFO windows. The last probably offers the most instant fun, so I'll concentrate on that here. Mystic (like Prologue and Spector) provides two independent LFOs and, as can be seen in the screenshot above, the speed, depth and wave type of both the LFOs can be easily configured. The LFOs can then be assigned to modulate a number of Mystic's key controls by clicking within the Mod Dest or Vel Dest window and selecting a parameter from the drop-down list. The editable value next to the parameter controls the degree of modulation, and assignments within the Vel Dest box are also influenced by note velocity. As can be seen in the screenshot at the top of this page, an LFO can be assigned to more than one parameter.
Good potential targets for the LFOs are the Cut, Morph, Damping and Feedback controls, as all these parameters influence the tonal qualities of the sound. Negative values can also be set, changing the direction of the LFO modulation. If a slow evolution of the sound is required, a slow speed value and the sine, ramp up or ramp down settings provide a good starting point. A faster LFO speed can produce more rhythmic effects — and the 'Arhythmic Chaos' preset provides an excellent example of this. If you want to create something that sounds a little more disturbing (and less melodic), target the Detune, Crackle and Pitch controls... things can get ugly very quickly!
Both the ENV and Event windows give access to further options for developing evolving pad sounds. Envelopes can be assigned to modify Mystic controls. For example, the Cut value could be altered by Envelope 3 and therefore change with time. However, LFO speed and depth can also be controlled via an envelope, and any of the parameters controlled by the LFO will thus also be influenced by the envelope. For hands-on control, Mystic parameters can also be assigned, in the Event window, to the mod wheel or aftertouch (if your master keyboard supports it), and this allows you to control how the sound evolves as part of your performance.
Finally, I must sound a brief note of caution... Mystic can generate a fairly powerful output when its controls interact, so make sure you practice 'safe sound-making': experimenting at a modest monitoring level will ensure that you avoid nasty surprises. This aside, it should all be plain sailing, with a surprising array of sounds waiting to be coaxed out of Mystic's depths.
Don't Just Read It: Hear It!
To complement this article, we've placed some audio examples, along with descriptive commentary, on the SOS web site, at: www.soundonsound.com/sos/jun08/articles/cubasetechaudio.htm