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本帖最后由 RotenLA 于 2011-7-7 22:32 编辑
今天偶然在网上看到的,大概的介绍如下:
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.
大伙儿自己慢慢看吧,另附上一个Demo Program,官网也只有这一个免费的Demo。可以用Demo对比着上面的参数进行研究~这个Demo适用于PC3,PC3K,PC3LE。
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