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Synthesis  |   Control  |   Technical description
Express yourself with KFM

FM (frequency modulation) synthesis was made famous by the Yamaha DX7, and is arguably the most successful and sought after technique in the history of sound synthesis. KFM controlFM synthesis thanks its success to the expressiveness it enables. Sounds can change dramatically, depending on how they are played. Also, FM synthesis provides a refreshingly broad timbral palette, ranging from emulated acoustic instruments to avant-garde, techno or spacey sounds. No wonder that FM synthesis, after twenty years of duty, is still in the centre of the music community's attention.

For a long time, it was generally assumed that FM synthesis is simply impossible to realise with Kurzweil's Variable Architecture Synthesis Technology (VAST).

Forget what you may have believed - DLN Sound proudly presents KFM, opening up the world of FM for your Kurzweil synthesizer. Sounds with all the expressiveness associated with FM. No samples or other trickery are involved; sounds are genuinely FM synthesized using standard VAST processing. If you want to understand how that operates, read the technical description.

KFM combines FM synthesis with the numerous other capabilities of VAST, multiplying up to a sheer infinite sonic potential. Also, the unbelievable KDFX effects have been optimised per individual KFM sound.

KFM brings you expressive sounds for your Kurzweil synthesizer with timbres previously unheard of, and virtually impossible to achieve on any other instrument. You do not need to invest in expensive hardware upgrades, or even new equipment. No sample memory is needed. Sounds load blazingly fast in a matter of seconds - and they stay in your instrumentís memory even during power off.

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Real-time KFM control

Each and every KFM sound takes advantage of the unmatched controller capabilities of the Kurzweil synthesizers. Key velocity, after touch, sliders, wheels all change the sound's characteristics, from subtly to dramatically.

Controllers have been meticulously assigned per individual sound for maximum musical usefulness. The assignments follow certain conventions to make it easier to remember them. Also, the conventions let you intuitively reach for the appropriate physical controller on your instrument for what you want to achieve. Note that, when of musical benefit for specific sounds, controller assignments may differ from the conventions. The conventions, as well as the actual controller assignments are listed in the product's Musician's Guide, which is available for download in the products section.

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Realising FM with VAST

If you are familiar with FM synthesis, and want to understand how it can be realised using the standard processing blocks of Kurzweil's VAST synthesis engine, read this description. But fasten your seatbelts - it is assumed that you have a basic knowledge about mathematics and of VAST principles (e.g. that the SHAPER block actually calculates the sine value of its input signal). If that is too much for you, just skip the formulas and jump to the conclusion below. In the mathematical description, constants and factors are omitted for clarity - it just sticks to the essentials.

So first the rocket science. An FM operator (as Yamaha calls it) with time dependent frequency modulation input signal in(t), envelope env(t) and output signal out(t) can be expressed as:

out(t) = sin( ωt + in(t) ) * env(t)
which due to the periodicity of 2π of the sine function is equivalent to: out(t) = sin( (ωt mod 2π) + in(t) ) * env(t)
It turns out that this FM operator expression maps 1:1 to certain VAST processing blocks: sin( (ωt mod 2π) + in(t) ) * env(t) =
SHAPER( SAW + in(t) ) * GAIN
where GAIN has an envelope (e.g. AMPENV, ENV2 or ENV3) as control source.

The conclusion is that the VAST chain of blocks:

→ SAW+ → SHAPER → GAIN →
(with GAIN being controlled by an envelope) is EXACTLY an FM operator! There are many more FM operator incarnations possible in VAST (using other blocks like SW+SHP, !GAIN, !AMP etc) but essentially they are all the same in their operation.

By putting multiple of these FM operators (of several VAST blocks each) in series, FM 'algorithms' can be built. The K2000 and K2500 can support 2-operator or (with limitations) 3-operator algorithms. With these, many of the most famous FM sounds can be realised, like the ubiquitous electric piano and tubular bells DX7 presets. The K2600 and K2661, with their Triple Modular Processing (cascading of 3 VAST layers), allow dauntingly complex FM algorithms to be constructed.

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