Advanced Synth Features
A glossary of advanced hardware synthesizer options and synth sound design capabilities
Often, when comparing hardware synths versus one another and trying to make a decision on which synth is more versatile or a better value or match for one's needs, people tend to just focus on the big picture specifications - ie: Total number of voices, oscillator types, filter types, total amount of modulation sources and mod matrix size. These are definitely key considerations that determine the synth's potential sound and versatility.
But beyond the obvious specs, there are many more advanced features that should be considered if you're hoping to achieve a versatile range of sound design. These features are often listed in the fine print, or not at all in marketing materials, but they all can offer unique sounds and capabilities, and when combined together, the capabilities and versatily of a synth can increase dramatically if these advanced features are included:
- 1. Voice Architecture and Sound Engine Features
- 2. Advanced Envelopes
- 3. Advanced LFOs
- 4. Advanced Modulation Matrix
- 5. Advanced Sequencing
1. Voice Architecture and Sound Engine Features:
The core sound engine consists of the oscillators, noise sources, or external input sources that act as the sonic foundation, as well as the filter and amp architecture that is used to subtract away and shape the sound. Each voice will have its own independant set of oscillators, filters, amps, lfos, envelopes, and other elements that allow a given voice to be articulated independantly per key that is pressed.
a. High Voice Count
The most modern analog flagship poly synths now offer high voice count options. Four voices is an absolute minimum for qualifying as a real poly synth, and many synths are now offering options for 12 voices and 16 voices. You might wonder why you would ever need 16 voices, considering you've only got ten fingers that could possibly press keys at a given time. The reason is that after you release keys and move fingering, there is a release stage of each voice that continues to "ring out" depending on the release settings in the filter and amp envelope sections. For stab type of sounds, and most leads and bass sounds, this is not an issue, since you generally play fewer notes, and they have short release times, but for large cinematic type of sounds, pads, and some string or brass sounds, you may have fairly long release times / fade out times. If you're playing chords with root or octave root bass notes, and moving around the keyboard, you may experience "voice stealing" where voices that are in their smooth release phase are suddenly cut off abruptly. This is generally unwanted behavior. On a poly synth with only 4-6 voices, this voice stealing is likely to happen with long release time sounds. However, with 12-16 voices, it is generally not a problem / not noticable. So, high voice count is a major consideration if you want to create cinematic type of sounds, big pads, strings, or brass sounds with long decay/release times.
b. Multi-Timbral Splits and Stacks
Multi-timbrality is an advanced feature that allows the synth to divide its voices into two or more sections that can be played on separate sections of the keybed (SPLIT), or layered together for complex sounds (STACKED). Advanced flagship analog poly synths offer at least bi-timbral architecture (2-sections of timbrality), or tri-timbral architecture like the Moog One. For live players, having a split mode with the lower keyboard section playing a bass tone and the upper section playing a lead tone, strings, arpeggios, pads or other sounds is vital, and allows the synth to essential act like two separate synths in one unit. With a bi-timbral or tri-timbral stack mode, you can layer two significantly different tones to create unique sounds that would never be possible with a mono-timbral poly synth. For instance, you could have one layer play a percussive piano type of tone, and the other layer play an ambient pad or evolving motion sound that fades in, and for every key you press, you get both sounds. Bi-timbral or better architecture opens up a world of possibilities. In addition, you can use a bi-timbral stack to layer to identical sounds (or nearly identical sounds) to create huge binaural stereophonic type of sounds.
Further, some synths offer "full multi-timbrality" of all voices. There's not a lot of modern analog synths that offers this mode, but it essentially allows every voice to have its own completely separate sound design. Full multi-timbrality is mostly useful in scenarios where each layer can have its own sequence or arpeggio playing. You can create a few layers with drum type of sounds (hats, bass drum, snare), another voice playing a monophonic bass line, and a couple more layers to play melodies or harmonic content on top. The ultimate flagship synth would offer full multi-timbral capability for its voices, but also have a way to which voices are grouped together. For instance, if you could devote four voices to drum and bass sounds that play sequences based on a key played in the lower half of the keybed, with a four over four stack on the upper section of the keybed that plays a bitimbral stack for strings, pads or other sounds. This would be a very special high end option.
c. Versatile Analog and Digital Oscillator Selection
There are a variety of oscillator types and sub-categories that modern synths may offer. At the widest angle view, we can categorize them as either Analog or Digital in nature. Analog oscillators are generally considered more desirable due to their sound character. Specifically, analog oscillators don't experience aliasing that can be present on digital oscillators. It is important to note though, with modern digital oscillators and NCOs, this is basically a non-factor now. Analog oscillators may also have minute differences in specific contours of their sound waveform, resulting in slightly different harmonic series emphasis. Also, there are some other quirks that VCO Analog Oscillators have, such as harmonic frequency jitter, and unique "tuning character", that is generally preferred by professional synth players. You can read a ton more about this topic in the Technical Articles on this Website.
On the digital side of things, basic digital waveshapes that model analog (VA - Virtual Analog Synths) have come a long way. Aliasing is basically a problem of the past, and digital oscillators can perform in a manner that is virtually indiscernable from their analog counterparts. Digital oscillators are also more likely to include true sine waves for certain types of sound design or sub bass tones. And on the advanced side, digital oscillators may have the capability for custom single cycle waveforms to be loaded (like Prophet VS, and now many modern synths). Digital oscillators are also far more capable of producing FM (frequency modulated) sounds with accuracy. At the top of the digital oscillator pyramid is Wavetable Oscillators, which is basically a stack of single cycle waveforms that can be scanned/interpolated between in real time, radically adjusting the tone and harmonic series of the sound generation based on modulation or the turn of a knob.
Some of the advanced flagship synths nowadays offer a combination of Analog and Digital Oscillators, giving you the best of both worlds, and the widest range of sound generation options. Synths like the DSI Poly Evolver, Sequential Pro3, Korg Minilogue XD, and Korg Prologue offer a combination of analog and digital oscillators.
d. Oscillator Cross Modulation / PolyMod / Frequency Modulation / Amplitude Modulation / Sync
Another advanced oscillator feature to look out for is cross modulation of one oscillator onto another oscillator. Most synths offer a Oscillator Sync option that resets the phase of the target oscillator when the source oscillator completes its cycle. When you have two oscillators sync'd with different frequencies (and modulation of those frequencies), you can get all sorts of cool tones. Listen to the lead sound of The Cars "Let's Go" for one of the most famous examples of oscillator sync.
Next up is Frequency Modulation of one oscillator to another. This is sometimes referred to as FM, sometimes PolyMod, and sometimes just XMod or Cross Modulation. The effect of FM can range from subtle wobbling tones to crazy metallic and bell type of sounds. Not all synths offer true oscillator FM / cross modulation, so this is something to look for as an advanced option. Note: some synths that don't offer direct FM of oscillators do still allow you to route LFOs (low frequency oscillators in the mod section) to an oscillators frequency. This type of modulation is still accurately called FM, though it has a more limited range, as LFOs don't go high into the audio range of frequencies. You can still pull off many classic FM tones though with LFO FM, such as the pitch warbling sound of Gary Numan's Cars.
Amplitude modulation is similar to FM in that you're taking the output of an oscillator (or LFO) and routing it to another oscillator - however, in the case of AM, you're modulating the overall volume of the target oscillator, instead of modulating its frequency. AM at audio rates (via AM osc routing) can create a bunch of interesting tones and ring modulation type of effects at high rates, or can create a wobbling tremelo type of effect at lower rates... great for modeling Wurli piano type of patches.
e. Advanced Oscillator Shaping / Shape Mod
Many modern oscillators (both digital and analog) also feature unique capabilities to warp or blend between core shapes of the oscillator. Classic synths either had selectors to switch between a Triangle, Pulse or Saw, or combos of the core shapes where they are layered together. Modern synths take it a step further and offer smooth, variable transitions between oscillator cores. For instance, you might be able to swing a knob, or modulate a parameter to smoothly transition between a Triangle shape and a Sawtooth. This is referred to as Shape Mod, and each synth has different options available. Beyond core shape blending, some synths offer additional oscillator wave mangling effects like wave-folding / metalizer effects.
f. Oscillator Phase Modulation / Phase Distortion Options
Most advanced synths offer a way to have free running oscillators that may or may not be in phase at a given time, but also offer a "Key Sync" button that causes the phase of each oscillator in the voice to be reset to its starting point upon a new key strike. This is an option that you should make sure is included, as it is important for some sounds designs, such as precision, hard attack bass sounds, or phasie pad and other ambient sounds where you want some phase randomness. Some advanced synths also offer additional phase control on a per oscillator basis. By offering a phase offset option (0-360 degrees), or a way to modulate oscillator phase starting positions, additional advanced sound designs can be acheived.
2. Advanced Envelopes:
Envelopes are at the core of sound design. They are the primary temporal modulation source that can turn a hard lead sound to a brass sound to an ambient pad sound, just by making a few ADSR adjustments for filter and amp envelopes. But not all envelopes are created equally. Here are some of the more modern, advanced envelope features.
a. Extra Envelope Stages
ADSR envelopes are the standard vanilla flavor (attack, decay, sustain, release stages), but modern synths can include an additional Delay stage before the Attack, and Hold Stage after the Attack. DADSR and DAHDSR envelopes offer additional flexibility for sound design. The pre-delay stage can be used to bring in a temporal motion after the main timbre of the sound is established. The hold-stage after attack acts like another timed sustain phase at the maximum value.
b. Adjustable Envelope Slopes
One of the hottest topics in emulating classic synth character is the behavior of envelope stages - not the timing of the stages, but the contour of change in the stages. The majority of synths offer just one pre-defined contour - usually an exponential/logarithmic type of curve that defines how the ADR (attack, decay, release) stages progress from their initial value to their target value. Some synths in the past have offered just linear/straight motion. The most flexible/advanced modern synths offer the ability to choose between two or more contour behaviors, or have variable adjusted contours. This allows you to alter sounds to be snappier (great for some bass, lead sounds), or more linear or convex for other sounds (pads, strings, or other evolving sounds where you want a smoother attack or decay) There is a technique known as Recursive Envelope Modulation that can allow you to alter envelope slopes, however it's complex to implement and get the type of fine tuned envelope shaping that is possible with direct hardware/software implementations that target the contours. For more info on Recursive Modulation, you can read here: Recursive Envelope Modulation on Synths
c. Loopable Envelopes
Another modern feature that is becoming more standard on synths is a switch on envelopes to make them loop. Rather than progressing once through their stages, they continuously loop around Attack and Decay/Release stages. From a practical standpoint, this allows envelopes to act like and extra, customizable slope LFO that repeats. For synths with limited amount of LFOs, this can be a vital addition to expand LFO and animated capabilities of a sound. For synths with plenty of LFOs, it can just add another "variation" of an LFO that has unique contours based on the Attack and Decay values set for the looping envelope. Any way you look at it, having a switch to convert a given envelope into a loopable envelope is a great option.
d. Multiple Envelope Retrigger Options
Most synths offer at least a choice between Legato and Staccatto type of envelope retriggering. This behavior occurs Per-Voice usually, although it is possible that synths offer a sort of monophonic retriggering scheme option that is global to all poly voices. With Legato mode, the Attack and Decay phases run in sequence when you first hit a note-on until they reach the Sustain hold stage, but if you keep that note held down and play additional notes in sequence, the Attack and Decay stages will be skipped on additional notes, and the envelope will remain in its Sustain stage value. This is used to create bass or lead sounds where the initial note hits have a more dramatic envelope amp or filter curve, but additional notes played legato style will be more subtle. With Legato Mode off, the synth switches into a more Staccatto type of envelope retriggering, where the Attack and Decay Stages always restart with each consecutive note press, whether or not there are additional keys held down at the time. Normally, in Legato mode, the Attack stage will start at wheverer the previous envelope on that voice is currently at. The previous triggered envelope may still be in its Attack/Decay stage, resulting in a much smaller attack delta amount, or if the envelope had already reached the sustain phase or was in release stage, the attack delta amount may be greater. There is another advanced option that some synths offer for Always Retrigger From Start (0-point) in Staccatto mode. This resets the envelope to zero and starts the attack fresh for every key press, no matter what stage the envelope for that voice was previously in. This option is useful for patches where you always want a consistant Attack for each note or chord strike.
e. Separate Retrigger Options
Some synths like the Subsequent 37 offer separate multi trigger switches for each envelope, rather than having the Retrigger Setting affect all envelopes together. This allows you to have the Filter Envelope set to retrigger always, while keeping the Amp Envelope in a Legato mode, or vice-versa. This option could also be extended to Auxiliary Envelopes as well. The ability to control the retriggering type of each envelope independantly increases the sound design options and allows for very interesting lead and bass sounds where you play in a legato style, but get partial retriggering on some envelopes.
3. Advanced LFOs:
LFOs are one of the primary sources of motion and texture in a given sound design. They can be used to give your patches vibrato (either natural, or on tap via key pressure), turn square waves into modulated pulse waves for lush PWM sounds, or for a variety of other modulations including oscillator shaping, amplitude modulation, frequency modulation, and other animated sounds. It's common for modern flagship synths to include 2-4 LFOs. Two is really a bare bones minimum to accomplish versatile sound design options, and four or more LFOs is prefereble. Below we look into some additional advanced LFO behaviors and options.
a. Multiple Unique LFO Shapes
The basic shapes that are virtually always present are Triangle, Saw, Square and Random. (Square is sometimes called Pulse and Random is sometimes called Sample and Hold / SH) In addition to the basic shapes, some synths offer two flavors of Saw. A standard Saw / Declining Saw, plus the opposite Ramp Saw / Inclining Saw shape. Some synths also allow adjusting the Square/Pulse width, from a short blip to a 50/50 square to a short blip in the opposite vector. Some advanced synths offer both Triangle and Sine wave LFOs, which gives additional flexibility for tremelo/vibrato type of textures. In addition, some synths offer adjustable contours / shape modulation of LFOs. Having extra LFO shaping options extends the capability to create unique pulsing sounds, and fine tuning the behaviors of tremelo/vibrato/PWM effects.
b. LFO Phase Adjustment
Most synths have the ability to key sync the LFOs, so when you strike a key, the LFO for that voice is reset to its starting point. This is useful for many sound designs, rather than having the LFOs always free running in the background. For more advanced options, many synths offer the ability to adjust the Phase Alignment of the starting point for the LFO, so that it starts at a different point than the default. For a Pulse/Square, you might have a default starting phase when the pulse is at its highest point, and then it drops to the lowest point of the pulse at 50% of the way through the LFO cycle. By using a phase offset, you could set the start point to be the 50% location, and then every time you strike your key sync'd LFO, it will start with the 0/lowest point and then jump to the high point. This is very useful if modulating pulsing pitch effects, and other special effects.
c. LFO Slew Adjustment
Some synthesizers offer a slew control for LFOs, which round the edges of hard envelope contours, like Saw and Square fronts. Slew can turn a Square LFO into a square with rounded edges, which glide into high and low values. Applying slew on a Triangle LFO can round off the points at bottom and top to give more of a Sine Wave shape.
d. LFO Polyphonic / Mono Switch
Most modern polyphonic synths have LFOs that operate on a per voice basis. For instance, if you've got a 16 voice Rev2 or Moog One, there are actually 16x the amount of LFOs that are on the panel. (one LFO running for each voice x however many LFOs are on the synth) This provides an amazing amount of rich tones and organic variation when they are free running or key sync'd with slightly different key strike times. However, for certain sound designs, and emulating some classic synths that only have monophonic LFOs, it's a useful feature for synths to include a button that forces Polyphonic LFO setups to operate like Global/Mono LFOs. A Global/Mono LFO will always keep the modulations of all voices in perfect sync / in phase with each other. This is useful for sound designs where you want an overall sweeping motion of filter cutoff point, or other parameters.
4. Modulation Matrix
Custom modulation routings are at the heart of advanced sound design. Most every synth has a bunch of hard wired modulations for envelopes to filter/amp, velocity to amp and filter, key tracking to filter, and other common routings that have dedicated knobs on the front panel. The Modulation Matrix of modern flagships is where they become more than just a synth of the 1980s, and venture into unknown new territories of sound design, and into the world of modular synthesis. Most modern flagship synthesizers now include at minimum 4 customizable mod slots, and many synths will offer 16, 32 or even more custom mod slots. This allows you to reroute a variety of sources and destinations, exploring the depths of modular synthesis and making unique and nuanced sound designs.
a. Expanded Modulation Sources
There are a variety of mod sources that are considered standard and normal for matrixes, like velocity, aftertouch, note number, envelope sources, lfo sources, plus contols like mod wheel, sliders, pedals, pitchbend. If the modulation matrix runs at "audio rates", it may also include oscillator sources that can be routed for FM/AM effects, beyond any dedicated Polymod/Crossmod controls. Some more unique Mod Sources to look out for include DC (a fixed offset), Random (a Random Number Generator per key strike), Voice Number (a set offset based on voice number triggered), and additional sources based on Sequencer, External Audio Inputs, or CV inputs from the synth. Having expanded sets of Mod Sources allow more unique modulation behaviors and more organic textures if doing Voice Modeling.
b. Mod Matrix Transforms
Most Mod Matrixes include just the Mod Source, the Mod Amount, and the Mod Destination. For more advanced control, some synths, like the Moog One, offer an extra layer of interpolation in between the Source and Destination. This can be a simple math transform like multiplication or division which allows you to expand the range of modulation, or get finer values, or it may be a more advanced transform like a squaring or square root operator that adjusts and creates a slope/contour for the modulation, min/max levels which can cap modulations at strategic intervals, and a variety of other operations that alter how mod transforms behave based on input and over time. Mod Transforms, while on the surface might not seem that exciting, are actually an extremely powerful sound design tool that can be used to give patches nuanced behaviors, or create unique modulated animation and textures.
5. Advanced Sequencing
Many mono and poly synths offer built in note sequencing and/or modulation sequencing. The basic specs of a sequencer section will usually include the amount of tracks available for sequencing and the total amount of steps that the sequencer holds per track. For instance, the Sequential Pro 3 features 16 modulation tracks, each of which can have up to 64 steps, or alternatively broken down as 16 steps x 4 phrases. Note sequencing generally always includes the basics of note number, velocity and duration per step, but some sequencers offer additional features to create much more nuanced or procedural patterns.
a. Step Ratcheting
Sequencer step ratcheting is an effect where a note is triggered multiple times within a single step. For instance, ratcheting x2 would subdivide the step length, and trigger the note twice within the period of one step. Ratcheting is a popular effect to acheive Aphex Twin style rapid fire note triggering.
b. Holds, Ties and Glides
Most sequencers offer a way to hold or tie notes together for different lengths. In addition, offering the ability to overlap notes for legato glide is another great option for sequencing.
c. Probability, Randomization and Humanization
Many sequencers offer some sort of humanization controls like adding predefined swing to the note trigger timings. More advanced sequencers also offer setting per step trigger probabilities (0% to 100%) that create some randomization and chance for steps to not trigger, giving you interesting patterns with ghost notes or constantly varying patterns. In addition, some sequencers also offer velocity and duration randomization options which varies the velocity and duration of notes for each step, by a set input amount. With these type of features on the sequencer, you can design a general foundation for the rhythm/sequence, but have lots of variation, creating procedural sequences that never repeat exactly, and offer much more interest to the listener, as they are more organic and human like in their performance.
d. Adjustable Track Step Count and Step Order
Having the ability to alter the amount of steps on a per track basis allows creation of complex poly rhythmic type of patterns, when you play multiple sequence tracks with differing lengths. In addition, some sequencers allow for juggle up the direction of the step progression (forward, backward, forward>back) or randomization of step patterns.