Taking the design of the original Minilogue and features from the Prologue, does the XD offer the ideal balance between function and price?
The XD looks and feels like an enhanced Minilogue. It shares the same design, the same four-voice polyphony, a similar control panel, and the same velocity-sensitive mini-keyboard. But when you delve beneath its surface, it becomes clear that the XD has far more in common with the Prologue than is immediately apparent. The addition of the digital Multi Engine in the oscillator section is the largest indicator that the XD is a close relative of the Prologue, but there are others. In fact, the voice structures of the XD and the Prologue appear to be almost identical except for the fact that the output from the XD's voice mixer is a single channel of audio, whereas each voice on the Prologue can be panned in a stereo field. But while much of the technology inside the XD appears to make it a Prologue wolf in a Minilogue sheep's clothing, spending time with it showed that this can be misleading too.
Like the Prologue, the XD is a true hybrid, offering analogue and digital oscillators, analogue filters and amplifiers, but digital LFOs, contour generators and effects. The VCOs offer the traditional three waveforms — sawtooth, triangle and square — and a range of footages from 16' to 2' which, together with the ±2 octave performance switch, allow you to program everything ranging from deep, grumbling basses to the highest pitched whistles, the latter with an admirable absence of aliasing. Add waveshaping, cross-modulation and sync, and you're not going to run short of analogue timbres. Alongside these, the digital Multi Engine offers three additional sound‑generation capabilities, including 16 variations of 2-op FM synthesis that can generate a range of tones that would be impossible to obtain from the analogue oscillators. There are also four digitally generated noise algorithms, and 16 slots for user-programmed digital oscillators.
There are several other changes in the XD's oscillator section when compared with the original Minilogue's. For example, you can now modulate the pitch or waveshape of oscillators individually, allowing you to create chorused sounds and other effects that were not possible on the earlier synth. In addition, the issue with the discontinuity in sync sweeps is gone, although this is a side-effect of a change in the contour architecture (which we'll address shortly) rather than any obvious differences in the oscillators themselves. But perhaps the weirdest change is the way in which the oscillators are pitched. On the original Minilogue, the sawtooth wave sat an octave above the square and triangle waves unless you applied waveshaping, at which point it dropped to the same octave. On the XD, it sits at the same octave unless you apply waveshaping, at which point it's an octave lower.
More changes can be found in the filter section. Unlike the original Minilogue (which offered both 12dB/oct and 24dB/oct low-pass filter options) and the Prologue (which combined a 12dB/oct low-pass filter with a simple high-pass filter), the XD offers just a low-pass filter that, although not advertised as such, I suspect is a 12dB/oct design similar to the Prologue's. It sounds good, and its two levels of overdrive allow you to craft a wide range of timbres from it. What's more, it passes low frequencies faithfully at high resonance, and it tracks the keyboard almost perfectly so you can use it as a fourth oscillator or to create the kind of breathy 'tuned noise' patches that I enjoy. Apart from key-tracking of 0, 50 or 100 percent, you can adjust its cutoff frequency in five ways: manually, using external CVs (which we'll come to shortly), using the LFO, using the assignable AD contour generator, and using velocity to affect the depth with which the AD contour is applied. Happily, the control panel switch that selected between just three velocity sensitivities on the Minilogue has been replaced by a menu that offers much finer values ranging from 0 to 127.
The output from the filter, together with the output from the Multi Engine (if programmed to bypass the filter) passes next to the audio amplifier. As on the previous models, this is controlled by an ADSR contour generator. The amplitude of the contour is again velocity sensitive and, again, there's a menu parameter that allows you to adjust the sensitivity from 0 to 127.
The XD is not deeply endowed with modulation generators or routing options. Unlike the Prologue, which offers three LFO options — fast, slow and bpm (internal clock or external sync) — the single LFO per voice on the XD offers normal (which spans the same range as the slow option on the Prologue), bpm and one-shot, the last of which allows you to use it as a very basic but useful secondary contour generator. Sadly, the Minilogue's facility to control the speed and intensity of the LFO using the assignable contour generator has disappeared, and the loss of the Prologue's fast range means that audio‑frequency filter modulation is no longer possible, which precludes some of the wilder sounds of which the larger synth is capable. You can still control whether the LFOs in all of the voices are locked together or not, and whether they are key-sync'ed or not, but only one destination can be selected at a time and there are only three LFO waveforms which, unfortunately, don't include noise or Sample & Hold. However, there's a huge improvement over the previous models to be found here: you can control the LFO rate and intensity using CVs.
As for the sounds themselves, these ranged from the simplest timbres to immense soundscapes, from delicate fairy-dust patches to overpowering lead synths and basses.
Now we come to the assignable contour generator. Whereas the Minilogue and Prologue incorporated a second ADSR contour generator, the XD offers merely an AD contour on which, if appropriate, the decay continues as a release after you've released the key. What's more, the number of destinations for this is reduced. These might seem to be small changes, but they're not. Furthermore, the XD shares one of its predecessors' deficiencies: at just three seconds, the slowest attack times — whether you're using the assignable AD or the amplifier's ADSR — are too fast. Sure, you can use the LFO in one-shot mode to create slower sweeps, but that limits you in other ways. The contours are generated digitally so I have no idea why Korg limited them in this fashion.
The outputs from the XD's four voices are summed as determined by the Voice Modes (which include an arpeggiator offering no fewer than 13 algorithms), and the signal is then passed to the digital effects sections. These are far more advanced than the simple high-pass filter and delay line provided by the Minilogue and, in one important aspect, offer a huge improvement over the Prologue's effects. The first of the XD's effects sections includes 27 modulation effects — eight choruses, three ensembles, eight phasers and eight flangers — with eight slots for user‑programmed effects. This is then followed by two further sections comprising 12 delay/echo effects and 10 reverbs. The improvement is that, whereas the Prologue allowed you to use a modulation effect and a spatial effect (delay or reverb) simultaneously, the XD — despite the manual stating otherwise — allows you to use a modulation effect, a delay and a reverb simultaneously. Control is limited to just Time and Depth for each of the effects, but there's still a great deal of flexibility on offer, especially since all six parameters are also CV destinations. Unfortunately, the maximum gain in the feedback loop of the delays is a tad under unity so, as on the Prologue, you can't create the sci-fi effects that could be obtained from the Minilogue.
Like the original Minilogue, the XD incorporates a 16-step polyphonic sequencer. This offers step and real-time recording, rests and ties, gate length and swing, plus four channels of motion sequencing (a posh name for automation) of many of the voicing parameters. Once a sequence is recorded, you can play over it using any unused polyphony and, if you press too many keys, polyphony will be stolen from the sequence itself. This means that, with clever programming, you can achieve more than you might expect. Unfortunately, there's no way to transpose a sequence while it's playing, which is a significant shortcoming, but you can record transposed sequences in adjacent Programs and switch between them while the sequencer is running. Using the sequencer is a doddle, and I have to compliment Korg's programmers on a very transparent and intuitive system for all of this. Each Program has its own sequence memory, so the current sequence will be stored with the current sound if you save it. But beware... you can't attach a sequence to a different Program, which means that, if you want to perform the transposition trick, you have to program the sequence from scratch every time. What's more, if you select a new Program without saving a sequence, it's lost. You have been warned!