The Sylenth 1 from Lennar Digital is a VSTi plug-in, so it requires a VST host program. There are a number of commerical music production products like Ableton Live and Cubase that can server as a VST host. I use a free program simply called VSTHost that so far has been sufficient for my experimentation.
I have been using the free demo version of Synlenth 1 that disables some features and has less preset sounds. It also announces "Thank you for using this demo." every minute. (I tried to record around these announcements but occasionally you will here it in the samples.)
The screenshot above shows the Sylenth 1 interface within VSTHost. It has the look and feel of a vintage analog synthesizer with knobs, switches and sliders. You twirl the knobs, slide the sliders, and flip the switches with the mouse. Sylenth 1 has four software oscillators that generate tones using sine, square, saw, and other waves, with frequencies controlled by the keyboard. Each oscillator has controls for pitch (octave, note, and fine tuning), volume, wave phase, and stereo effects. Each oscillator also has up to eight unison voices. I initially didn't get the reason for multiple unison voices (just louder?) until I learned about the "detune" control which allows the tuning of the voices to vary slightly, producing a richer sound. The oscillators are organized in two parts (A and B) and only one part is displayed at a time. Each part has an envelope control which affects the attack (A), delay (D), sustain (S), and release (R) of the generated tones. Each part also has a filter that can modify the tones by filtering out high or low frequences. The result of the two parts is then combined by the mixer.
Sylenth 1 also has two low frequency oscillators (LFOs) two modulation envelope (ADSR) controls, and two miscellaneous controls that can be used to modulate the generated tones. (In the demo version only one LFO, one modulation envelop, and one miscellaneous control are enabled.) Each of these can be set to control up to two parameters for the other components. In the screen shot LFO 1 and the key velocity (how hard the keys are pressed) control the filter cutoff frequency for the combined A aand B parts.
At the bottom of the screen there is a keyboard that can be played (but not well) by the mouse, and the traditional synthesizer pitch bend and modulation wheels, also used through the mouse (which is difficult while playing a real keyboard). MIDI keyboards more expensive than mine have their own pitch bend and mod wheels that can be used instead. Finally the Portamento knob controls the "glide" between two notes.
This synthesizer has a number of built-in effects, shown as vertical tabs in the middle of the screen: distortion, a phaser, chorus, equalization, delay, reverb and compression. Each of these have controls that can be set to modify the effect.
The arpeggiator plays sequences of notes based on a played chord (arpeggios). It can be set to play notes in ascending or descending order, or both, or random. The arpeggiator can also be programmed to play up to 16 notes based on transpose steps from a pressed key. With the arpeggiator you can play quite complex music using just simple chords.
The settings of all of the controls can be saved and recalled as a preset. A sound bank is a collection of presets. The Sylenth 1 demo comes with 128 presets, some of which are sampled here. The full price version has over 1300 presets. You can buy additional sound banks from sound designers like www.vstsoundbanks.com. The presets in the demo are grouped as follows