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MasterClass: Propellerhead Thor

March 7, 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.


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.

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.

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.


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.

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.

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.

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.

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