Raspberry Pi Wavetable Synth Complete

via the Raspberry PI Synthesizer blog:

"Time to call it a day and say yes, this thing is feature complete.

Feature set :

Single EG per note, 2 LFOs per polysynth
LFOs have sin, saw, square, tri and S/H modes
LFOs may optionally be synced to sequencer clock - the one feature not *quite* implemented yet
One LFO is always on, the other is ramped up by the Mod wheel

2 layers of wavetable trajectories ('oscillators') per note
Each wavetable trajectory consists of up to 8 wavetables, traversed in
- linear time
- quadratic time t*t
- inverse quadratic time 1-(1-t)*(1-t)
- exponential time - half-life a go-go
There isn't an EG to drive trajectory, just a dTrajectory/dt parameter. Trajectory resolution is always normalized to 1.0 irrespective of how many tables are in the trajectory, so a dTraj/dt of 0.5 will take 2s to pass through all the tables, unlss the linearity parameter is set to exponential, in which case the 0.5 is interpreted as a half-life, so after 0.5s you will be half way through the trajectory list, after 1s at 0.75 etc. Exponential is nice as you always have some movement going on, no matter how long you hold a note, but obviously you are getting asymptotic to 1.0 after a while.

The trajectory traversal may also be modified with both the LFO and MOD LFO, with programmable sensitivities. This gives really great slow movement for ever, even on non-exponential settings
Pitch of oscillators may be modified by both LFOs with programmable sensitivities - great slow movement plus crazy MOD wiggling
Oscillator B may be manually detuned / uptuned by +- 12 semitones, with exponential control for fine detune
Oscillators are MIP-map antialiased, the octaves generated by FFT / de-FFT, and there's a secret sauce trick that can be manually enabled to preserve the phase of certain harmonics whilst retaining my 'must have' / non-negotiable feature of a positive-moving zero transition at table location 0 for all octaves.

There is a back-end LPF, which is a truly brainless 1st order thing but it does go truly transparent at half Nyquist. This is just one filter per polysynth, effectively a very coarse tone control to tune out the psychotic edge of the more extreme waves and bring in some 'mellow', if mellow is what you fancy. This is nice on lush ensemble stringy sounds to push them more background but leave their tones prominent to reinforce a melody.

There are some 21 built-in wavetables - I need to count, there may be just 17 - there are more than 16, I broke the nice power of 2 limit because I had some I couldn't bear to leave out. These include 3 Caitlin vowels, sampled piano, brass, alto sax, viola, and also analytical waves like saw, sin, square, tri.

The Cray XMP / SIMD programming system is included, to support user construction of rich new wavetables from combinations of existing tables, be they built in or user-programmed.

Nice feature set, eh?

A first generation Raspberry Pi seems to be able to generate about 20 notes of polyphony from this synth, which is a lot of synthesis. So a completely reasonable thing is to create 4 PIANA Virtual Analog monosynths, 3 PIANATRON sampled synths and a pair of 4 note polyphonic PICYCLE wavetable synths, and let them go play.

Obviously on a Raspberry Pi 2 you can do all this and find a cure for the common cold in parallel using neat protein folding tricks. Or just fire up another dozen synths and go really crazy.

This thing sounds even cooler than I imagined, and to be honest I always expected it to sound cool. But it is BRILLIANT. Seriously.

Video to follow.

p.s fave trick to date - the Gordon Reid 'strings' trick with a Slightly Phase Distorted pair of different stacked sawtooths, one FMd by a 3Hz 0.08 semitone amplitude S/H LFO. Lush ..."