MasterClass: Propellerhead Thor

March 16, 2017

Few soft-synths have stood the test of time like Propellerhead Thor. Introduced 10 years ago, Thor remains the centerpiece of Reason’s synthesizer suite and is also available as an iOS app. As a result, the synth has achieved a serious following, thanks to its collection of vintage-inspired oscillators and filters, modulation matrix, and ability to route signals in ways we associate with modular gear. This month we’ll explore ways to make greater use of the powerful engine lurking under its hood.

Fig. 1. Thor’s Mod Envelope stages can sync to tempo and loop, enabling it to double as an LFO.

 

 

Fig. 2. Global Envelope, in conjunction with its global filter, lets you re-create ’70s-era paraphonic synths with ease.

 

MODULATION

Starting with tips on modulation tools may seem a bit unorthodox, but in the case of Thor it makes sense because the synth’s distinctive envelopes, LFOs, and step-sequencers are the keys to unlocking its design resources. With a modulation matrix that accesses nearly every synthesis parameter, understanding the possibilities is essential.

Envelopes. While the amplifier and filter envelopes are straightforward ADSR affairs, the Mod Envelope offers unique features that make it useful for a variety of alternate applications (see Figure 1). For example, its delay, attack, decay, and release parameters can all be quantized to note values and synced to tempo–fantastic for dance music. If you want to create a filter decay that’s exactly one measure, just turn on tempo sync, set the decay to 4/4 (four quarter notes) and you’re in business.

Another handy feature is the ability to loop the delay, attack, and decay parameters, creating a customizable LFO. Want a classic sawtooth? Set the attack to zero and the decay to a longer amount. Ramp up? Invert those values. Triangle? Set them both to equal amounts.

There’s also a fourth global envelope that works in a paraphonic manner (see Figure 2). That is, it affects whatever it’s assigned to in monophonic fashion with “single-trigger” operation, much like an old-school string synth such as the Moog Opus 3. This means that the envelope doesn’t retrigger until all keys are lifted, at which point it resets. This envelope also includes an additional hold segment between the attack and decay—great for creating the punchy sound of vintage Moogs.

LFOs. Thor’s dual LFOs offer a lot of exotic functionality despite their deceptively simple layouts. For starters, there’s a much wider range of waveshapes than you’ll find on most synths: Eighteen in total. Fortunately, every waveform is displayed graphically. It’s also worth noting that the last nine shapes are stepped and can be used for faux arpeggiation effects when applied to the oscillators, or pseudo step-sequencer patterns when applied to filters or other timbral destinations.

 

Fig. 3. In addition to tempo-sync, the primary LFO can also deliver audio-range modulation with scalable keyboard tracking.

Although the LFO’s rate parameters can be synced to tempo, in standard mode they extend into the lower audio range, which is fantastic for nasty FM effects. Additionally, LFO 1 includes a key-follow parameter that lets the rate track the keyboard, with higher notes increasing in speed accordingly (see Figure 3).

Whereas LFO 1 is polyphonic, with a discrete instance for each voice, LFO 2 is paraphonic—like the global envelope—and affects all voices simultaneously. This is great for ’80s funk chord stabs (a la Prince) when used in triangle or sine mode and applied to pitch. Of special note to Deadmau5 fans: Setting LFO 2’s waveform to the downward saw-like shape, with a synced eighth-note rate, and applying it to filter cutoff, results in his trademark “pulsed chord” effect.

Step Sequencer. Thor’s integrated step sequencer is deep enough to warrant its own tutorial, but in the interest of our emphasis on sound design features, we’ll focus on setting it up exclusively as a parameter modulation tool. For that, just toggle off all of the red switches under its 16 steps. This deactivates the note triggers, leaving its dual curves available for sequencing the values of destination parameters assigned to it. With forward, backward, two types of “pendulum” (back-and-forth), and random modes, Thor’s step sequencer is a powerful modulation feature for complex rhythmic/tonal patterns.

OSCILLATORS

Now that we have a handle on Thor’s modulation amenities, it’s time to explore their applications. Thor’s audio path includes six oscillator types that can be configured in countless ways, offering a vast range of synthesis techniques.

Each of the oscillator modes is based on a different synthesis type, including analog, FM, wavetable, phase modulation, multi-oscillator, and noise. Connoisseurs may immediately recognize the original sources for all of these models, but the bottom line is that each option is sonically distinctive.

Analog. While this oscillator is the most familiar, it’s worth noting that the pulse width is continuously variable, so classic pulse-width modulation—via LFO or envelope—is available. Square waves are produced at the 50% setting and the extremes are either 0% or 100%, which result in no sound. This may be a bit confusing for newcomers, especially with extreme modulation amounts, which may cause the oscillator to unexpectedly cut out.

Pro Tip: Apply one of the step sequencer curves to the pulse width for unusual rhythmic timbres, especially where the modulation can reach the extremes of 0% or 100%, creating a gated effect.

Pro Tip 2: In sine wave mode, you can use the oscillator to reinforce the fundamental and add body to a patch, or add low-end boost when tuned an octave lower.

Wavetable. Fans of the groundbreaking PPG Wave 2.x synth from the early ’80s may have noticed that Thor includes 11 of its original wavetables, which are great for re-creating vintage sounds from Depeche Mode and The Fixx (“PPG 2 Bell” is a standout here). Propellerhead’s original wavetables are equally useful for metallic textures that evoke that retrowave sound. Whereas the LFO and step-sequencer are modern approaches for animating the wavetables, purists should opt for the mod envelope with a long decay and release.

Fig. 4. Tucked away on the left side of the interface are Thor’s hard sync buttons, which allow for sync effects, even on FM and Wavetable oscillators

Another interesting trick is to place a wavetable oscillator in the second or third oscillator slot and then sync it to oscillator 1. This vastly increases its timbral range, since changing the tuning—especially by large amounts, such as octaves—delivers dramatic harmonic shifts.

Pro Tip: The hard-sync option also works on the FM and Phase Modulation types, which is an extremely unusual feature for any synth (see Figure 4). Additionally, when re-tuning the synced oscillator to higher octaves, low frequencies are generally attenuated. Consequently, blending in the analog oscillator’s sine waveform (described above) helps retain the fundamental, keeping the result full-sounding.

Phase Modulation. This form of synthesis was originally called “Phase Distortion” when Casio introduced its CZ digital synths in the mid-’80s. In use, Thor’s PM oscillator morphs a sine (or sine-like) wave into a complex shape that resembles common analog waveforms (see Figure 5). To get the hang of this oscillator type, start by leaving the second modulation wave off, set the PM amount knob to maximum, then scroll through the eight waveform options on the first modulator to hear their timbres. Next, turn the PM knob back to zero to hear the transition between sine and the selected shape. As with the CZ, selecting one of the five waveforms for the second modulator shifts the timbre further, by alternating it with the first selection.

 

Fig. 5. Based on the Casio CZ Series, the phase modulation oscillator can be extremely dynamic when modulated via velocity.

 

It may sound complicated, but in practice, configuring the PM oscillator is straightforward. The PM knob behaves similarly to the cutoff of a lowpass filter, but with a different nuance when modulated via Thor’s tools.

Pro Tip: While envelope and LFO modulation options are the obvious choice for animating oscillator textures, for real-time performance, try using velocity on the PM amount (or wavetable, pulse width, etc.). This can be a dramatic way to add dynamics to your patches.

Fig. 6. Even though it’s limited to a single carrier/modulator pair, the FM oscillator is capable of evoking many of the DX7’s signature sounds. Shown here is the configuration for the “future house” bass sound that’s currently in fashion.

 

Frequency Modulation. If you’re a DX7 fan, this oscillator is a great way to add a slice of its sound to your patches. Although Thor’s FM tuning options are integer-only (no clangorous bell tones here, sadly), its palette is broad enough to generate many familiar DX tonalities quickly. The secret is to use one of Thor’s envelopes as the modulator envelope—a central component of FM synthesis. Once that’s set up, it’s just a matter of selecting a carrier/modulator ratio that captures the sound you’re after (see Figure 6).

Here’s a handy cheat sheet for the ratios of classic FM sounds (with carrier in the first position):
1:1 Great for electric bass or plucky synths in the mid-upper range.
1:2 The essential “future house” bass sound.
1:3 Basis for the DX7 “Jazz Guitar” patch.
1:4 Square-wave-like, often used for simulating woodwinds.
1:5 – 1:10 Bells, mallet percussion, chimes. 1:10 and greater: Glistening tones, with some of the same qualities as the classic DX electric piano.

Multi Oscillator. Roland introduced the “supersaw” in the JP-8000 synth back in 1996, and it quickly dominated both trance and EDM for two decades. Thor’s Multi Oscillator re-creates that supersaw, while offering additional waveforms and detuning algorithms. For those looking to avoid the obvious EDM applications, this oscillator is wonderful for thickening the sound of other oscillator types. Set it to either the muted saw or square waveform, increase the detuning, then mix it behind your timbral oscillators. It adds a richness that’s subtler than simple chorusing.

This oscillator can also create massive THX-style rises for dance music and film soundtracks. While most of the detuning algorithms are dissonant at their extreme settings, “Oct UpDn” and “Fifth Up” transform in a very musical manner.

For a dramatic build, try this approach: Assign the modulation wheel to control the detuning amount via one of the previously mentioned algorithms; or better still, use each mode on a separate oscillator. This way, you can precisely control the duration of the rise in real time or with automation.

Fig. 7. Thor’s Noise Oscillator offers a surprising range of textures and is a fantastic resource for audio-range modulation when applied to the other oscillators’ pitches

Noise Oscillator. While noise is a standard tool in any synth’s arsenal, Thor’s array of noise generators are the most versatile I’ve ever encountered. The white and colored noise offer the most familiar results, while the “static”, “S/H” and “band” modes can be used for clever sonic tricks in conjunction with the Noise Mod parameter (see Fig. 7). Here’s a cheat sheet for those effects:

Static: Noise is generated via an increasing number of random static clicks. Turning the knob from low to high increases the click rate until the sound transforms into white noise. If you want to add “vinyl noise” to a lo-fi sound, try this mode.

S/H: In the early days of arcade video games, explosion sound effects were created with an audiorate sample-and-hold. Here, the knob functions in a similar manner. To create chip-tune effects, apply an envelope to this parameter and adjust the modulation amount and envelope decay until you hit the target.

Band: I’m a fan of “sonar pings,” which are normally created by passing white noise through a resonant low-pass filter. Here, one knob handles the heavy lifting for dialing in that tone, offering a wide range of pitched noise textures.

Pro Tip: This is huge, so pay attention. Nearly every audio source in Thor can also be used as a modulation source. That means you can take the output of an oscillator and use it to modulate another parameter. To experiment with this feature, begin with a noise oscillator and route it to the pitch of a sawtooth oscillator, listening to the results as you tinker. For example, with the noise oscillator’s knob set to its lowest values, the static mode adds tiny glitches to the sound, the S/H mode delivers random effects quite unlike the LFO options, and the band mode adds a rapid, chaotic drift to the pitch, like a swarm of bees.


FILTERS

Thor’s filtering options are equally extensive, though the types may be a tad more familiar. Even so, there’s one detail worth mentioning before you begin experimenting: The default settings for all filters include envelope modulation with depth controlled by velocity. This is a great starting point for beginners because it is dynamic and the dedicated knobs are a huge plus. That said, seasoned programmers often find themselves turning it off every time they start a patch. Try creating an “init” preset that’s identical to the default, but with those envelope parameters set to zero.

Pro Tip: All filters include a drive fader, which adds warmth, volume, and distortion when maxed out. Because this can also be modulated, you can create dynamic overdrive by routing a touch of velocity to control this parameter. A little goes a long way, because volume is also affected. Experiment until you find a value that matches your playing style.

The filter types are Ladder (an emulation of the Moog lowpass), State Variable (multimode with an Oberheim flair), Comb and Formant. While the first two modes should be familiar to EM readers by now, the second two are worthy of a closer look.

Fig. 8. While many designers use comb filters for flanging effects, here it’s set up for re-creating Karplus-Strong synthesis.

Comb Filter. For many synthesists, comb filtering can be a bit confusing. At first listen, it sounds like an intense flanger, which makes sense, since both are based on a network of one or more delays with extremely short times. Sweeping the frequency knob is a great way to generate flange effects, to be sure (see Figure 8). However, because of its delay-based structure, comb filtering is also a fantastic way to get into Karplus-Strong synthesis, which is how many physical modeling synths create plucked string effects.

Here’s how to get started with this type of synthesis: Reset Thor to its defaults and turn off envelope modulation to the filter. Select the noise oscillator and reduce its mixer volume (the 1+2 fader) to zero. Then, modulate the volume of 1+2 with a very fast mod envelope with instant attack and short decay. The result should be a short click, also known as an “impulse.” From there, change the filter type to comb and increase the keyboard tracking and resonance to maximum. If you’ve set it up correctly, you’ll immediately hear a pitched string tone like a clavinet. Welcome to Karplus-Strong!

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