Polysix and Korg MS20. The LAC-1 is available as a free upgrade, but has to be requested by the current owner of the OASYS from Korg. MOD-7: Optional (originally $249.00, but now available for free) that Combines Variable Phase Modulation (VPM), waveshaping, ring modulation, PCM sample playback, and subtractive synthesis in a patchable, semi-modular synthesizer. The MOD-7 is available as a free upgrade, but has to be requested by the current owner of the OASYS from Korg. HD-1 HD-1 Program The HD-1 is a sample+synthesis engine with a two "oscillator" structure. In addition to the two "oscillators," an HD-1 Program contains a Vector Envelope, Common LFO (per-program as opposed to per-voice, similar to the modulation LFOs in some early polyphonic analog synths), two common key tracking generators, KARMA settings, and effects. HD-1 Oscillator Each "oscillator" consists of a sample playback oscillator, dual multimode filter, nonlinear "drive" and low boost section, amp, and pan. The sample playback oscillator has four velocity zones, each of which can play a mono or stereo sample or a Wave Sequence. Velocity zones can overlap or crossfade. Korg claims very low aliasing distortion, due to the use of band limited interpolation. Wave Sequencing Wave Sequences were first introduced on Korg's Wavestation synthesizer, released in 1990. Wave Sequences allow a single note to play through a list of samples, one after the other, with or without crossfades, with other associated parameters changing for each sample, as listed below. This can create smooth, evolving timbres, or rhythmic effects. Internally, Wave Sequences are implemented by using two voices; voice A plays the first sample, voice B plays the second sample, voice A plays the third sample, and so on. Other synthesizers have featured concepts which are similar in some aspects, such as PPG, Waldorf, and Access Virus wavetables, Synclavier resynthesis, and Ensoniq Transwaves and Hyperwaves (see the Ensoniq TS 10). In the lists below, features new to the OASYS (in comparison to the Wavestation) are noted. OASYS Wave Sequences include, for each step: The sample to play (mono or stereo) Sample start offset Reverse on/off The length of the step, in milliseconds or rhythmic value The crossfade time into the next step, in milliseconds Crossfade fade-in shape (256 steps, from log to exp) Crossfade fade-out shape (as above) Volume Transpose and fine-tune Two modulation ("AMS") value outputs, to control any assignable parameters of the synthesizer in the rest of