声音的亮度明暗 {滤波器 (Filters) }

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Filter滤波器这也是最具合成器特色的功能参数（在类比合成器的时代合成器的代名词），在电压控制的模拟合成器上经常写成VCF(Voltage Controlled Filter)

著名Filter：Moog Ladder Filter、Oberheim SEM State Variable Filter

Cutoff截止频率：是滤波器中控制声音明暗（determines the brightness of synth——Control brightness with cutoff）的最主要的参数，以Low Pass Filter (LPF)为例，截止频率设定在2500Hz，就会过滤掉高于2500Hz的频率。
Low Pass Filter:The most common synthesizer filter. A Low Pass Filter is an extreme filter that allows all frequencies below the cutoff frequency to pass through while rejecting (attenuating, lowering) those frequencies above the cutoff frequency.

-more cutoff= rounder and darker until the fundamental pitch is eliminated, making the sound disappear completely

-Less cutoff=sound gets brighter and edgier

-Reducing cutoff by a little bit doesn't change the sound much, but it reduces the amount of sizzle(zzzzzzzz) sound making it cleaner.

-Think of this sizzle as a noise osc seperate from the osc

通过LPF滤掉一些频率的同时，整体的声音响度也会变小，所以要和音量Main Volume同时使用。

（-If the cutoff is too low, the volume of sound gets low; to make up for this volume loss, we turn up the volume）

-This is great for making bass patches and other round, dark sounds.

滤波模式/滤波器类型：

    1. L/Low/Lowpass：低通，保留低频过滤掉高频(LPF)

    2. H/High/Highpass：高通，保留高频过滤掉低频(HPF)

    3. Band/Bandpass：带通，只留下中音频率，将高低频去掉(BPF)

    4. Peak：截止频率的增益

    5. Notch：陷波，滤掉中音，留高低频（Band Reject）

滤波衰减斜率SLOPE，数值越大斜坡就越陡，衰减得越厉害

6, 12, 18, 24 dB/oct

•1, 2, 3, 4 pole

•1 pole = 6dB

LPF与HPF的串联与并联