Kyra's FPGA-based synth engine is technologically innovative, but what's it like as an instrument?
Two years ago I reviewed the Waldorf Quantum, a superb synthesizer that I view as the company's finest achievement to date, so it was with some excitement that I approached the Kyra. This feeling was enhanced by its reassuring size and weight as well as its smooth, wobble-free knobs. I was a bit surprised by its small monochrome screen, but it was only when I looked at its rear panel that I was marginally disappointed; I have no idea why Waldorf used 1970s-style black plastic quarter-inch sockets and ring nuts and allowed them to protrude so far.
The Kyra's basic unit of sound is a Patch, but you can program and play one of these only when it's inserted into a Part. This contains additional parameters — MIDI channel, level, pan, transposition, output pair and so on — that are edited and saved as part of an enclosing Multi. There are eight Parts within each Multi and these can be split by restricting them to constrained keyboard ranges, layered by making them respond to the same MIDI channel, or used multitimbrally by allocating different channels to each, or any combination of these. There's no voice stealing between Parts, so you can think of the Kyra as eight individual virtual analogue synthesizers drawing from a common pool of Patches. The strange bit is that you're always in Multi mode, so you only ever have access to Patches within the Parts of a Multi. Furthermore, the Part doesn't contain the Patch; it only points to the original so, if you modify and save a Patch within one Multi, you'll affect the same Patch in every other Multi that uses it.
The memory holds 128 Multis plus 3328 Patches spread across 26 banks, the majority of which are described as ROM. But, while you can't overwrite individual patches in the ROM banks, you can transfer banks of Patches to them, so it's not ROM at all but some form of flash RAM. However, it's the genuine RAM that worries me. The manual explains that this is maintained by a rechargeable battery that, in the absence of mains power, will sustain the memories for just a few months. If you're accustomed to synths that haven't had their CR2032 batteries changed in decades, you'll have to keep a close eye on this.
Rather than provide conventional VA oscillators, there are two Oscillator Groups (OGs) in a Kyra Patch, and these offer two modes of sound generation: Wave and Hypersaw. The first of these allows you to program the OGs independently, with each offering three simultaneous waveforms: sawtooth (actually a ramp), pulse and Wave, the last of which accesses a library of 4096 public domain single-cycle waveforms. Waldorf often refer to these waves as wavetables, but don't be misled; there's no wavetable synthesis on offer. There's hard sync of OG2 by OG1, and frequency modulation of OG1's Wave by OG2's. An Auxiliary oscillator control in OG1 offers two additional functions, acting as the volume control for a white noise generator in both OGs, or as the volume control for the output from a ring modulator that uses the Waves selected in OG1 and OG2 as sources. Consequently, you can't obtain ring modulation and noise simultaneously, and you can't generate different noise levels in each of the OGs. Each OG also boasts a detunable sub-oscillator offering four waveforms. This is a separate entity from the ramp, pulse and Wave generators because it doesn't contribute to, and isn't affected by, FM, sync or ring modulation. This makes it useful for enforcing the fundamentals of exotic timbres generated by sync and, in particular, FM.
Selecting Hypersaw mode defeats OG2 and causes OG1 to generate six detuned sawtooth waves as partials. You can control the spread of these partials as well as their loudness distribution and their stereo width to create anything from gentle chorusing to insane amounts of wobbling. In addition, a sub-oscillator function can steal two of the six partials and detune them by an octave. Hypersaw generates a limited but important range of sounds, including ensembles as well as many useful pads. However, I found that my Hypersaw Patches distorted unless I reduced their volumes to as little as five or six out of 127. One consequence of this was that, when I used MIDI CCs to fade Hypersaw sounds in and out of a performance, the coarse quantisation made this less smooth than I wanted.
The levels for the various waves generated by the OGs are mixed within the Groups before passing to the two filters in the filter section. These offer six filter types — low-pass, band-pass and high-pass, each with 12dB/oct and 24dB/oct options. Waldorf describe these as "accurate emulations of classic analogue ladder filters" and claim that "higher [resonance] values can cause large resonant peaks and, ultimately, self-oscillation" but nothing in the Kyra's filter section would cause it to self-oscillate in any conventional fashion, even if I used the...