A MPLITUDE E NVELOPE S ETTINGS Four points

1. (Blue) 0.00, 0.00 2. (Yellow) 0.02, 1.00 3. (Red) 0.08, 0.45 4. (Blue) 0.25, 0.00 VelSen: 0.740

Filter Controls

The filters in Crystal are similar to those found on many synthesizers, but with a few extra features.

There are the typical controls for selecting the filter type, setting the filter ’s cutoff or center frequency, and the resonance or Q of the filter. There is also a dedicated envelope generator that modulates the cutoff or center frequency. In addition to these standard filter controls, there are two extra control sliders, labeled Saturation and Shaper. We will look at these functions more in Chapter 8 when we talk about amplitude distortion effects. For now, know that Saturation applies a “tubelike”

distortion to the filter ’s output, while Shaper creates a small distortion in the audio signal before it enters the filter.

The filter types in Crystal are the commonly found lowpass, highpass, bandpass, and notch filters with both resonant and nonresonant versions of the lowpass (ResLoPass, Low Pass) and highpass (ResHiPass, High Pass) filters. There is also an extra version of the resonant lowpass filter

(XResLoPass) that has a richer sound than the ResLoPass filter.

Like most synthesizers, there is only one control, a slider labeled Freq, for the cutoff or center frequency; it adjusts between 50 Hz and 17.1 kHz. Whether it is the cutoff or the center frequency depends on the type of filter being used. When the filter ’s envelope is turned on, the frequency slider changes into two sliders, labeled LoFreq and HiFreq, that set the upper and lower boundaries for the cutoff or center frequency as it is modulated by the envelope generator.

The Resonance/Q slider changes its name and function depending on the filter type. For resonant filters, the slider controls the amount of resonance. For nonresonant filters, the Q slider narrows the width of the transition band.⁴

Focusing the Timbre

With the filter envelope off and the saturation and shaper sliders turned all the way down, select Low Pass as the filter type and push the cutoff frequency all the way to the right and the Q slider all the way to the left. While sustaining a note on your keyboard, gradually lower the cutoff frequency until the sound completely disappears. When that happens, the filter ’s transition slope is entirely below the frequency of the note you are playing.

Move the cutoff frequency up to around 5 kHz and notice that the sound is still rather dark, with only a little high-frequency content.⁵ Since the Q slider is all the way to the left, the slope of the filter ’s transition band is rather steep, thus eliminating most of the high frequencies. Begin moving the Q slider to the right—decreasing the steepness of the slope—and the sound begins to brighten as

more high frequencies are allowed to pass.

Position the Q slider in the middle and play a note while moving the frequency slider back and forth. Notice the sweeping timbral shift as the cutoff frequency moves higher and lower. Now switch to the ResLoPass filter type and, again, sweep the frequency slider. For comparison, try the same thing with the XResLoPass filter type. With both the ResLoPass and XResLoPass filters, the increased resonance adds a lot more focus to the sweeping of the cutoff frequency. Do you prefer the sound of the ResLoPass or the XResLoPass filter when you sweep its cutoff? What is the difference between the two?

Modulating the Cutoff

Select the ResLoPass filter type and turn the filter envelope on. Set the LoFreq slider to around 250 Hz and the HiFreq slider to around 15 kHz. From the filter envelope preset menu, select

UpFastDnSlow for the envelope shape, and position the Resonance slider at 0.500. Now when you play and sustain a note you will hear the cutoff frequency begin quite high and gradually drop down to 250 Hz as the sound continues. What happens if you increase or decrease the amount of resonance?

Sequenced Filter

Leaving resonance at 0.500, change the filter type to XResLoPass and choose Arpeggio from the filter envelope’s preset menu. In the next chapter, we will look at step sequencers and low frequency oscillators to create rhythmic effects in a filter, but Crystal allows you to do this right in the filter ’s envelope generator. With the Arpeggio envelope selected, the filter creates a pulsing timbral shift at the speed of the sixteenth note. Change the tempo in the keyboard window of the Crystal Player and note that the speed of the sixteenth-note pulsing stays synchronized to the new tempo.

Amplitude = Filter

With all the previous settings still in place, select Copy from the function/preset menu of the amplitude envelope generator and then select Paste from the function/preset menu of the filter envelope generator. This changes the filter envelope to be identical to the amplitude envelope. Since the attack and decay stages of this envelope are so short, the envelope creates a bit of a wow at the beginning of the sound.

Laser Blasts

Move the resonance slider all the way to the right, and the wow of the previous example becomes a high-frequency squeal as a result of self-oscillation in the filter. You can change the frequency of the

“laser blasts” by raising and lowering the HiFreq slider. Temporarily pushing a resonant filter into self-oscillation is a popular way to add the chirps one so frequently hears in synthesized sounds. As you did in Chapter 3, use the copy voice and paste voice functions to create a detuned multiwave oscillator with the same filter settings on all three voices.

These are but a few samples of what can be accomplished with audio filters. Here, we used only the most common type of filter for subtractive synthesis, the resonant lowpass filter, but dramatic effects can be created with any of them. Be sure to try out all the other filter types as you manipulate their controls in a similar manner to what you were doing in the examples above.

Using Your Own Synthesizer(s)

1. Where is the filter stage of your synthesizer(s)

2. Is there a global filter for the composite sound, or are there separate filters for all of the

oscillators or voices?

3. What types of filters do you have?

4. Do you have both resonant and nonresonant filters?

5. How is the transition slope of the filter measured: dB/octave, order, pole, Q, or something else?

6. For filters that have two transitions, is the slope measured with bandwidth, Q, or something else?

7. Do the filters have their own envelope generator, or do you need to assign an envelope generator to them?

8. Can you push your filters into self-oscillation?

Creating a sound with oscillators, shaping its amplitude, and manipulating the sound’s timbre are the basic elements of the synthesis process. Now it’s time to start modulating those elements with both internal and external controllers to bring a whole new level of dynamic control and musical quality to your synthesized sounds.

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