User manual ALESIS MODFX PHILTRE

[. . . ] Reference Manual This page intentionally left blank 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Copyright 2002, Alesis. All rights reserved Reproduction in whole or in part is prohibited. Specifications subject to change without notice. All trademarks are the property of their respective holders. [. . . ] The Master will send its digital audio output to the First Slave, and the First Slave will, in turn, send its output to the Second Slave. 24 3 Using the Philtre This section defines the different kinds of filters and modulations, and explains the functions of the Philtre's controls in greater detail. The technical information in the next few pages will help you get the most out of your gear. . . it's really pretty simple. What is filtering? An audio filter is a special kind of tone control that filters out certain frequencies. Just as a water filter lets water through but stops dirt and rust particles, audio filters let the frequencies you want flow through, while stopping the rest. Every kind of audio equipment has filtering or filter sections in it. If you have twoway speakers in your studio, each tweeter is protected by a high-pass filter that lets the treble through while keeping the bass out (so you don't blow the tweeter), and the woofer may be connected to a lowpass filter that keeps the high frequencies out. If you have threeway speakers, a band-pass filter lets only the midrange frequencies get through to the midrange driver. While most filters are used for equalization and crossovers, engineers discovered that powerful filters moved around dynamically could be a useful and creative special effect. The Philtre falls into this special class of filters, that includes wah-wah pedals and voltage-controlled filters on synthesizers. 25 3 Using the Philtre Filter curves, orders, and slopes When you look at a graphic display of their frequency response, every filter has a slope--gentle or steep, like the slope of a hill. The passband--the frequency range that the filter lets through--looks like a flat plateau. The frequency at the edge of that plateau, just as the response starts to go downhill, is called the corner frequency. Then, the frequency response goes down at a particular slope, measured in decibels per octave. The slope is determined by the number of components or poles in the filter. A simple single-pole filter, the gentlest kind, rolls off frequencies at a rate of 6 dB/octave above its corner frequency; a four-pole filter is a much steeper 24 dB/octave. In the Philtre, the PHREEQ control determines the corner frequency, and the STEEP switch allows you to quadruple the slope. The REGEN control increases gain at the corner frequency, further changing the filter characteristics. You hear this at high settings as the filter beginning to "whistle" as the harmonics near the corner frequency all begin to peak together due to phase addition; this is also called resonance or "Q". Modulating the filter frequency All the rest of the controls on the right-hand side of the Philtre are designed to modulate or dynamically change the filters' corner frequencies. If the DEPTH control is at minimum, and you move the PHREEQ control around by hand, you'll hear the effect of changing the corner frequencies. The Modulation section of the Philtre essentially does the same thing: it moves the frequency of the filter around dynamically, under control of an LFO (Low Frequency Oscillator). Not only does the Philtre give you a lot of modulation options, it can automatically synchronize the movement of the filter frequency with the speed of the music using the Tempo Sync features. 26 Using the Philtre What is Tempo Sync? Three of the five mod sources in the Philtre have a repeating cycle over time (Triangle, Sample/Hold, and Pattern). Sometimes, you'll want the rate of that cycle to match the beat of your music instead of being random. For example, you can set the rate so that the sweep of the filter completes each cycle once per measure, or to a tremolo-like effect that happens in sixteenth notes. The TEMPO SYNC feature of the Alesis ModFX series not only lets you set a tempo naturally by tapping on the TAP TEMPO button, it can automatically adjust its speed slightly relative to the audio input, after setting the basic speed using the TAP button. 3 To use Tempo Sync: You can set the Philtre to TEMPO SYNC mode as follows: 1. [. . . ] This warranty is enforceable only by the original retail purchaser and cannot be transferred or assigned. For the most effective service, the purchaser should register the purchase on the ALESIS website at http://www. alesis. com/support/warranty. htm. During the warranty period ALESIS shall, at its sole and absolute option, either repair or replace free of charge any product that proves to be defective on inspection by ALESIS or its authorized service representative. In all cases disputes concerning this warranty shall be resolved as prescribed by law. [. . . ]