Advanced dynamics and harmonics processing comes to Eurorack.
When the company behind the cult-favorite Mög four-band distortion pedal and module releases a module called Shape, you might expect it to be a waveshaper based on a distortion effect. And you wouldn’t be too far off the mark. However, DPW’s Shape SH-1 Spectral Enhancer has far more nuanced capabilities than simple waveshaping or distortion.
At the simplest level, think of Shape as a brick-wall limiter module, based around nicely rounded saturation rather than a hard clipping circuit. What sets Shape apart is that it also gives you separate access to this saturation behavior on transients and on the sound’s tail. You can mix them in to taste or patch them individually to other destinations. This allows you to design the final sound’s harmonic content well beyond just turning up the compression or limiting amount.
How It Works
Shape’s starting point was the circuit inside DPW’s L-1 Triple Limiter module. Both have a series of eight soft knee compression curves starting at ±2.5V (-6dB for a typical Eurorack ±5V audio signal), with a hard limit set at ±5V. Shape’s Drive control has roughly twice the range of the Limit control on the L-1, allowing a 10x signal gain compressed and limited to a ±5V output.
The image below shows the effect of setting Shape’s Drive control to 50% with a series of common synthesizer waveforms. The green trace is the original waveform; the blue trace is Shape’s Comp (compressor) output. I’ve pre-trimmed the input waveforms to be just under ±5v; the level of the incoming signal will interact with Drive to determine how much shaping takes place.
What the compression does is add upper harmonics to the sound. The figure below on the left shows the harmonic content of a pure sine wave: just a single fundamental harmonic at the note’s pitch. The figure on the right shows the harmonic content of our sine with 50% Drive; a lot of additional harmonic spikes appear, resulting in a brighter sound.
You can use Shape just as a compressor or hard limiter, increasing its Drive control to make the sound’s tail closer in level to its attack transient, while adding harmonics along the way. This sound appears on its Comp output. (Note that Shape’s sound is different from a typical compressor, which dynamically adjusts a signal’s level and can therefore pump and breathe; Shape is a saturator with fixed gain.) However, Shape also breaks out the sound’s transient and tail to their own dedicated outputs, Tran and Tail.
Remember that this shaping only kicks in when the incoming signal is above ±2.5V. So rather than patching Shape immediately after your oscillators—which usually have a steady full-level signal level—it’s far more interesting to patch Shape after you’ve dynamically processed a sound, such as after an enveloped VCF or VCA. It’s also very useful to patch Shape after a sample player with dynamic content such as drum loops, after percussion modules, or after sound or physical modeling modules that produce plucked or struck sounds. Dan Wahlbeck of DPW particularly likes its effect on complex wavetable-type and FM sounds.
When you do this, the sound’s initial attack transient—its loudest portion—will be shaped the most. This means that Shape will add the most harmonic content to the sound’s attack. The sound’s tail after the transient—usually at a lower level—will receive less shaping, or it might even be left alone aside from a boost in signal level. These are available at the Tran and Tail outputs, respectively.
Keep in mind that Tran is not the transient of the original signal; it is the processed transient, after it has been compressed, shaped, and therefore distorted (or harmonically enhanced, if you will). The Trim control allows you to remove as much of the original signal as possible to isolate this processed transient. Tail is the original sound minus the processed transient and is capable of exceeding ±5V in level. Both are affected by the Drive amount; Tail is not affected by Trim.
The Sum of the Parts
The DPW Shape module has a mixer section (outlined in yellow) where you can combine the original (Clean), compressed (Comp), transient (Tran), and tail (Tail) components together to taste. This is where you can really shape the final sound to your taste.
Adding Clean and Tail results in an enhanced or hyper-real version of the original sound that I personally find pleasing. Adding Clean and Tran results in a distorted attack without boosting the level of the sound’s tail, which gives you the dirt you’d hear on the Comp output without making the entire sound overbearing in level. And of course, you can come up with custom mixes that suit your own taste.
DPW suggests using the Tran and Tail outputs panned left and right to create a pseudo-stereo effect. However, Tran has its phase reversed compared with the input. (Look at the steady-state waveform examples above. To flatten the peaks of a triangle or sine wave, you need to subtract that shape from its peaks.) This might cause issues if you have to later collapse it to mono. If stereo enhancement is what you’re after, I suggest patching the Tran output through an inverter to make it phase coherent with the other outputs; it will still have different harmonic content to help spread out the sound in the stereo field.
Shape features an additional Aux input that’s hard to describe. Dan Wahlbeck himself admits it “is for experimental stuff just because I could add it.” He suggests using it “to process the same signal as on In via something that doesn’t add phase delay too much, like a ring modulator or something.” For example, patching a copy of the input signal through a lowpass filter and then to the Aux input will produce a sort of highpass-filtered sound.
The Shape of Things to Come
If you have been feeling your modular’s sounds—especially from your drum modules or sample player—are a bit unexciting, Shape is a good candidate to bend them into potentially more interesting sonic territories without extreme distortion. This is not a set-and-forget module, as the result varies greatly with different source material. The most glaring omission is the lack of voltage control over any of the parameters. If those had been implemented, you could sequence changes per song section or even note. DPW points out this would have raised the price, though. Even without this, Shape will still give you a very useful range of possibilities.
Synth and Software would like to thank longtime modular user and former synth designer Chris Meyer for his contribution. Chris is the force behind Learning Modular, where he teaches how to master modular synthesizers.