Файл: E-mu E 6400 EOS 4.0 manual.pdf

8 - Preset Edit

Dynamic Filters

Another characteristic of a filter is the number of poles it contains. Traditional synthesizer filters were usually either

2-pole or 4-pole filters. The Emulator has a selectable 2, 4 or 6-pole low pass filter. The number of poles in a filter describes the steepness of its slope. The more poles, the steeper the filter's slope and the stronger the filtering action. The tone controls on your home stereo are probably one-pole or two-pole filters. Parametric equalizers are usually either two-pole or threepole filters. In terms of vintage synthesizers, Moog and ARP synthesizers used 4-pole filters, Oberheim synthesizers were famous for their 2-pole filter sound.

Using a filter, we now have a way to control the harmonic content of a sampled sound. As it turns out, even a simple low pass filter can simulate the response of many natural sounds.

For example, when a piano string is struck by its hammer, there are initially a lot of high frequencies present. If the same note is played softer, there will be fewer of the high frequencies generated by the string. We can simulate this effect by routing keyboard velocity to control the low pass filter. The result is expressive, natural control over the sound.

272 E-MU Systems

8 - Preset Edit

Dynamic Filters

If an envelope generator is used to control the cutoff frequency of a filter, the frequency content can be varied dynamically over the course of the note. This can add animation to the sound as well as simulate the response of many natural instruments.

Parametric Filters

A more complex type of filter is called a parametric filter or Swept EQ. A parametric filter allows control over three basic parameters of the filter. The three parameters are: Frequency, Bandwidth, and Gain. The Frequency parameter allows you to select a range of frequencies to be boosted or cut, the Bandwidth parameter allows you to select the width of the range, and the Gain parameter either boosts or cuts the frequencies within the selected band by a specified amount. Frequencies not included in the selected band are left unaltered. This is different from a band pass filter which attenuates (reduces) frequencies outside the selected band.

Another parameter sometimes used on a parametric filter is Shelving. Shelving simply widens the passband so that it extends to the limit of the upper or lower frequency range.

The parametric filter is quite flexible. Any range of frequencies can be either amplified or attenuated. Several parametric sections are often cascaded in order to create complex filter response curves.

The Z-Plane Filter

A Z-plane filter is a filter which can change its function over time. In a Z- plane filter, we start with two complex filter types and interpolate between them using a single parameter. Refer to the diagram on the following page.

The Z-plane filter has the unique ability to change its function over time.

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8 - Preset Edit

Dynamic Filters

Filters A and B represent two different complex filters or “frames”. By changing a single parameter, the Morph, many complex filter parameters can now be changed simultaneously. Following along the Morph axis you can see that the filter response smoothly interpolates between the two filters. This is the essence of the Z-plane filter. Through the use of interpolation, many complex parameters are condensed down into one manageable entity.

Consider, as an example, the human vocal tract, which is a type of complex filter or resonator. There are dozens of different muscles controlling the shape of the vocal tract. When speaking, however, we don't think of the muscles, we just remember how it feels to form the vowels. A vowel is really a configuration of many muscles, but we consider it a single object. In changing from one vowel to another, we don't need to consider the frequencies of the resonant peaks! You remember the shape of your mouth for each sound and interpolate between them.

This Z-plane filter sweep can be controlled by an envelope generator, an LFO, modulation wheels or pedals, keyboard velocity, key pressure, etc. In fact, any of the modulation sources can control the Z-plane filter.

274 E-MU Systems

8 - Preset Edit

Selecting Voices, Samples & Groups

Selecting Voices, Samples &

Groups

When working on complex sounds we need an easy way to specify certain voices or groups of voices for editing. There are several ways to select Voices, Samples and Groups.

Selecting from the Preset Editor Windows

To select Voices, Groups, or Samples from any of the preset editor windows you simply move the cursor to the appropriate field and press the Edit key (F6). The label on the Edit key changes depending on which type of item the cursor is on.

•When the cursor is on any Voice-related Function, the Edit key will select Voice Edit.

•When the cursor is on the Group Number, the Edit key will select the entire Group.

•When the cursor is on the Sample Name, the Edit key will select the Sample and will automatically jump into the Sample Edit menu.

Here's another little trick to help you select voices from the Preset Editor Windows.

•Press and Hold the decimal point button while playing a keyboard key to select that voice. Repeatedly pressing the keyboard key will rotate through any other voices assigned to that same key.

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