The Native Instruments FM8 software synthesizer uses a technique called Frequency Modulation (FM) Synthesis to generate complex tones. This technique was invented by John Chowning while at Stanford, It was licensed to Yamaha, which used it in the popular Yamaha DX-7 digital synthesizer. The DX7 had a reputation for being difficult to program because of the complexity of FM synthesis and its own minimalist interface. Nonetheless there were thousands of presets available for a wide range of sounds. FM synthesis was especially good (in at least some opinions) at reproducing metallic sounds like the Fender Rhodes electric piano.
The basic idea in FM synthesis is to use the output from one oscillator as the input to modulate another oscillator. The basic FM building block is called an operator, which consists of an oscillator, an digitally-controlled amplifier, and an envelope generator. Operators are connected together to form an algorithm, the end result of which is the sound. The DX7 had six operators and 32 preset algorithms. The FM8 also has six general-purpose operators, labelled A, B, C, D, E, and F, but instead of preset algorithms it as an FM matrix which is used to connect operators into an almost unlimited number of algorithms. The FM8 Expert view shows the FM matrix and the operator settings.
The screenshot above shows the settings for the the relatively simple Horn preset, Here the D operator modulates the E operator, which in modulates the F operator to produce the final sound. You make a connection between two operators by clicking on the matrix cell for the row and column that contain the operator and dragging up or down to set the level (0-100) of the signal from one to the other operator. Each operator has a waveform (one of the usual sine, square, saw, or triangle waves, or more exotic waves like 1+n or nth formant) and a frequency ratio and offset from the note being played.These frequency parameters can add harmonics to the synthesized sound. Not shown in the screenshot are the Env graphical controls for the operators' envelope generators and the Mod modulation matrix. The Spec view shows the frequency spectrum and waveform generated by the algorithm. You can see how changes in the algorithm affect the wave. In addition to the six regular operators the FM8 has two special-purpose operators, X and Z, which have additional signal processing features like noise injection and filtering.
The FM8 has a large set of effects that can be applied to the synthesized sound: Overdrive, Tube Amp, Cabinet, Shelving and Peak Equalizers, Talk Wah, Phaser, Flanger, Tremolo, Reverb, Psyche Delay and Chorus Delay. Each effect that is active is represented by a panel with control knobs.
The FM8 also has a 32-note arpeggiator, with a visual pattern editor. Each note has. among other controls, an octave and transpose setting. These can be set to specific or random values. The speed of the arpeggio is controlled by the Tempo setting: beats per minute and note value (1/2, 1/4, 1/8, 1/16, and 1/32). There are many presets that use the arpeggiator to good effect.
I have been using the free demo version, which has all of the features and the 900+ presets of the full price version, but is limited to a 30 minute session and nothing can be saved between sessions. So you really can't create any new sounds with the demo version.
I initially had a problem with the sound quality (static or crackling) with this and other Native Instrument products. After some investigation I found that the problem could be resolved by setting the Latency (File > Audio and MIDI Settings) higher, to 896 samples. As far as I can tell this did not make a noticeable difference in the sound, other than eliminating the static.