Thor: Sonic Envelopes


Here are some audio snippets demonstrating the capabilities of Thor and the Infinity system. These short audio clips provide a glimpse into the possibilities that multichannel sustain and processing allow. I was contemplating on hiring a session musician to do some demos for me, like I used to before, but decided not to this time. After viewing online demos of guitars, I came to realize that most of these demos showcase the skills of the performer more than the instrument itself. I want to avoid falling into that trap. 

Infinite sustain presents some interesting performance challenges. Long sustaining notes are preferred over blazing fast runs. But there’s no polyphonic and melodic guitar music (beyond simply playing long sustaining chords) that I know of that satisfies what I have in mind. I imagine something like “Air in G” by Bach played on the guitar, if that is even possible! Articulation of each sustaining note is more important than trying to cram as many notes into each bar, flashy as that may sound. Vibrato and pitch bend of double and triple stops prove to be so much trickier to execute compared to monophonic leads, which kinda reminds me of the importance of a whammy bar (more on that later). The performance techniques are fundamentally different, and it will require really close collaboration with a session musician to give Thor justice.

As noted in the Infinity project white paper, the objective is processing the raw sound of the guitar and morph it into something entirely new. The audio clips presented below are all prepared using Logic Pro, using various plugins. I tried as much as possible to use only stock plugins, in addition to Ascend VPU which is staple in all the samplesIn some cases, I use 3rd party plugins, opting for free versions as much as possible. My main DAW of choice is Logic Pro, but of course, it is possible to use other DAWs such as Ableton or Reaper.

Each audio sample is recorded using only the Thor Infinity guitar. There are no other instruments. No synths, no drums, no bass. There are no overdubs, although there are a few takes and comps here and there. I will explain the processing involved below, for each audio sample.

Raw like Sushi

To set the baseline, here is a simple E chord. No effects, except the Ascend VPU preprocessor. Virtual Pickups Part 4 expounds on the importance of the preprocessor on each string. Basically, it is an inverse comb filter that negates the comb filter effect of the Nu Multi pickup. With preprocessing, the result is very rich, sweet and pleasing —very much like an acoustic guitar. You get all the full sonic range.

The first sample E chord is played by a soft downward thumb sweep the at the 24th fret:

The second sample is played using a pick:

Both are faded-out from 6.5 secs. The natural sustain is around 17 to 20 seconds.

This is the natural sound of Thor. No effects, sustain set to zero.

Signal Flow

The prototypical multichannel signal flow is as shown in the diagram below. Each string is processed by the Ascend VPU processor, followed by one or more insert effects. There may be one or more sends in each channel that goes to buses with send effects. Each channel strip and all send buses are then mixed to another “Poly Mix” bus with its own effects chain.


Single Notes

Thor has a single sustain level knob. The multichannel sustain driver listens to the inputs from each string and balances out the feedback loop to maintain this set sustain level. Too much drive can push the strings into wild oscillation, with the strings (especially the thicker ones) rattling against the frets, especially on setups with low action.

With external processing, as the Infinity system is designed for, a modest amount of drive should be enough. After all, one can use compressors to push this sustain level upwards to a preferred sustain level, and perhaps squash the attack transients, if desired. In this sample, we insert a compressor on each channel with the threshold at -25dB, and a high 30:1 ratio. Another post compressor is inserted as a mix effect, threshold at -25dB and 6:1 Ratio.

In this sample, we also demonstrate the use of pitch correction on each string. A touch of reverb completes the mix.


Notice the harmonics starting from 0:24. Such transitions from fundamental to the second harmonic are quite inherent in guitars, which typically have a higher second harmonic than the fundamental. This shift can be artistic and rather natural in electric guitars pushed to feedback, but can be unexpected and glaring. There are ways to mitigate this. One approach I did use pitch detection to sustain only the fundamental. This is one objective for the first release. 


The audio sample below demonstrates multichannel sustain. The compressor on each channel are set with threshold at -25dB and an 8:1 ratio. Each channel also has Logic Pro’s Enveloper effect plugin inserted with 50ms attack on each channel to give it a smoother attack.

Logic Pro’s Enveloper plugin, and similar plugins, leaves much to be desired. Such plugins rely on attack transients by analyzing increases in amplitude or power. Most performances do not have such cleanly defined attack transients. Note transitions such as legatos, for example, are not detected.

Envelope Shaping

Blackman Window
The Infinity system should not be limited to full sustain only. The idea is that we should have full control over the volume and timbre envelopes from note onset to note offset. In addition to note detection, I’ve also been working on onset detection. My goal is to use a fast and accurate onset detection algorithm for the envelope control. I am calling it Ascend ENV, which will be the second installment of the Ascend suite, starting with Ascend VPU. For demonstration, I inserted an early version of the plugin to transform the input’s attack and decay using a blackman taper window, giving the envelope a staccato effect.
The audio clip below is the raw, unshaped envelope. The notes are not picked, only hammer-ons and pull-offs using the right and left hand:
The audio clip below is the envelope-shaped result using an early version of Ascend ENV:

Not all staccatos are the same. The taper of the envelope is essential. A linear ramp or exponential curve (like those used in ADSR envelope generators) will sound very different. 

This is just a quick example. Imagine what can be done if we have full envelope control over the notes we play. Take note that Ascend ENV is a work in progress and is not available yet. Ascend ENV is an extended goal. Hopefully, I can have it ready in time for the first release.

Timbre Morphing

In this series of sample audio clips, we will apply different plugins to morph the sound into something entirely different. First, we apply a radical virtual pickup configuration with a highly unusual sonic character with pickups placed in unconventional positions, impossible to do in the real world:

This Ascend VPU setting, together with infinite sustain, and an interleaved left and right-hand tapping technique, yields a remarkably unique sound:

Now, we increase the sustain level using a compressor with the threshold set to -25dB and a high 30:1 ratio:

Now, the fun starts. Before Ascend ENV is fully developed, we will use other plugins to somehow approximate the desired effect. We will use AutoSwell Light (a free Automatic volume effect plugin) to give it a slow 100ms attack envelope:

Again, it’s far from perfect. Autoswell is not able to catch and quell the initial attack transient sufficiently, but it will do, for now. Ideally, you’d want to have a bell-like taper after onset detection, similar to what I did in the previous example, demonstrating proper envelope shaping using a blackman taper. A linear or exponential taper just wouldn’t do.

To transform the timbre, we use Voxengo Shinechilla Harmonics Synthesizer. This plugin allows you to generate and blend 2nd, 3rd and 4th harmonics with the original dry sound. We accentuate the 2nd and 3rd harmonics:

And here’s the result:

Ain’t that awesome cool? 🙂

Another plugin I have in mind is in the design stage right now, This audio plugin is specifically for spectral transformation, similar to what you see here, but much more. With pitch and onset detection, I envision an additive processor for controlling the precise amount of harmonics over time, increasing of attenuating the actual harmonics present in the incoming audio. This simple demonstration should be illustrative of the potential of that approach, but what I have in mind is so much more.


While the example above applies a static harmonics generator with fixed settings for the amount of harmonics added to the original signal, a subtractive filter, like the VCFs (voltage controlled filters) used in traditional analog synthesizers can also be used. Typically, you’d want to start with a signal rich in harmonics, but you can also use the additive harmonics generator above for that purpose. Then, the subtractive filter can effectively ‘sculpt’ the harmonics, following the signal’s envelope, giving the resulting signal a dynamic and evolving timbre over time.

In this example, I used Logic-Pro’s AutoFilter: a versatile filter effect for creating classic, analog-style synthesizer effects:

Like Logic Pro’s Enveloper plugin, AutoFilter’s envelope follower employs feature-based detection, which leaves much to be desired. It will do for now, but hopefully, Ascend ENV can do much better, with its true note onset detector.

Here’s the audio clip:

To sweeten the mix, there are some more additional processing worth mentioning:

  1. Like in the Triads example (see above), Enveloper is also inserted, with 20ms attack, on each channel
  2. Bass enhancer on Low E and A strings
  3. Vibrato on Low E and A strings (slow, but slightly different rates close to rate of lead vibrato).
  4. Slow Leslie on main mix

Next Step: Distortion

So far, we’ve covered clean sounds that we transform using various means into unique sonic textures. Multichannel processing gives us a lot of freedom to manipulate each string’s signal. In the next installment, we’ll get down and dirty with polyphonic distortion.
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24 days ago

I think Adrian Belew might be interested in this!

Would love your thoughts, please comment.x