Corona

Here are my thoughts on using this amazing synth for a few months. I'm mainly interested in programming analogue synth sounds from scratch, so that is my focus here:

UI:
Corona is easy to program due to it's clean interface and single-page layout. You can quickly get started on sound-design as it's simple to access a parameter and hear immediate results. I much like the subtle grey theme with the coloured controls.

Oscillators:
This is the outstanding feature of Corona, being typical virtual analogue, but with some truly unique audio modulation algorithms that I have not seen on other synths.

I have a deep affinity for analogue synthesis, but am often frustrated by a lack of imagination by designers when it comes to the oscillator section, considering that modern computing opens wide possibilities for waveform creation based on mathematical formulae. We all love the standard saw, square and sine waves as great building blocks in sound design, along with noise, FM, AM and RM, but eventually you hit a brick wall with what these can do on their own.

What the designers of Corona have done is to add bitwise modulation between the oscillators, allowing them to create sonically exciting textures that sound analog in nature, but with very rich overtones that are digital in a bright, aliased style, similar to 90's synths that had low bit rates.
All that is music to my ears, having grown up listening to the sounds of early samplers and hybrid synths that often failed to reproduce sounds accurately, but imparted a special character of their own.
To be fair, it's not to everyone's taste in sound design, but it covers an important niche in the history of electronic music.

From when I first installed Corona I found myself quickly coming up with sounds I instinctively liked and wanted to use in compositions. They had that aggressive analogue/digital crossover feel that gave weight to a track, especially in the bass, lead and pad department. And it also surprised me with some delicate - sounding imitations of acoustic instruments.
It certainly has that addictive tweak-factor that can go on for hours at a time, coming up with multiple variants of the same sound, starting with just the basic waveforms.
Even after a few months I have yet to fully explore all the different combinations of waves and audio modulation between the three oscillators, which goes to show what a great idea it was to include these algorithms.

My only criticism is a lack of explanation (or online info) for what the various formulas do to the waveforms: Okay, we know what AND and OR operations do to binary numbers, but what about their behaviour in an audio context? I have resorted to experimenting with just pure sine waves at various frequencies (and an oscilloscope) to try and work out how modulator and carrier interact, and which combinations produce good results.

Logically, it seems that when using bitwise operators the modulator is performing a type of amplitude modulation upon the carrier, a bit like traditional ring modulation. The difference being that the formula is going beyond normal multiplication of the two signal amplitudes, often resulting in some very digital-sounding artifacts.

If all this all sounds familiar, think of our initial experience with FM synthesis: randomly adjusting frequencies and levels in an attempt to produce musically pleasing sounds, but sometimes coming up with some real gems.

The Super 7 model does some very nice saw textures, but it's not clear how it interacts with the other waveforms and operators - I need to spend some more time playing with this.

Despite all this these are the best sounding VA oscillators I have heard.

Filters:
The filters certainly have a character of their own, which can take a while to get used to, but are powerful enough to tame the complex sounds coming from the oscillators.

The combination of the drive control and the shape selection takes time to understand as they both radically affect the sound of the filters, but they can add extra dimension to simple waveforms. Quantize shape is one of my favourites for adding top-end crunch.

They also self-oscillate nicely in tune, especially the phase models, and the smash model is great for OTT - sounding lead sounds.

I have found myself mostly using Corona's filters as a typical low-pass and high-pass combination to ensure that the output fits cleanly into the mix without too much low and high end distortion. They are an essential part of making the oscillators usable, considering the amount of digital harshness that can be present.

Envelopes:
Quick and easy to use, with precise time control and a good selection of shapes. A multi-stage envelope would be very useful for making drum sounds.

LFOs:
The usual shapes with handy tempo-syncing, but phase-offset and pulse-width would make them more controllable.

FX:
A very usable delay unit that ping-pongs quite rhythmically.
The limiter adds a nice bite and punch to sounds in combination with the envelopes.

Improvements:
A more controllable portamento feature.
A high-pass filter in the effects section to remove low-end distortion.
A signal-flow diagram would be most useful, as the way the 3 oscillators interact is not always clear.
Better fine-increment adjustment of the controls using the mouse scroll-wheel, and a clearer display of parameter values.

Conclusion:
Despite a few limitations, I'm really enjoying getting to know this synth, and the sounds it makes really do have a feelgood-factor that keeps me coming back.
Sure, it doesn't do everything more expensive synths do, and it does have a distinctively crunchy, digital sound when you open up the filter but I think it has a place in designing thoroughly analogue-sounding patches.
It's done a great job of creating those warm, rich brass pads that some synths struggle with and, after a bit of work, some glassy vibraphone pads.
And I've created some convincing cymbal sounds that are notoriously hard to program using analogue methods - which is where the bitwise operators have show their worth.
It's greatest strength is in bass, arpeggio and lead sounds that have real character and aggression when required, and all done with pretty minimal CPU demand.

Corona would certainly be in my desert island synth collection as it's constantly surprised me with the variety of sounds it can create.
Would I buy it again? Definitely, as no other VA has been as much fun to program.