EQ Magazine - September 2008 - (Page 44)

CHEAT SHEET MODULATION EFFECTS by Craig Anderton MODULATION LFO WAVEFORM FEEDBACK PHASE Cheat Sheet delivers concise, explicit information about specific recording/audio-related tasks or processes. This installment describes the parameters found in modulation effects such as flanging and chorusing. INITIAL DELAY This determines how the Low Frequency Oscillator-induced modulation varies over time. Examples: A square wave switches between two different delay times. A triangle wave varies linearly from a maximum to minimum delay time, then back again. A random wave changes the delay time randomly. MODULATION LFO RATE Also called Feedback Invert. Positive feedback feeds the audio back in-phase and creates a “sharper” sound. Negative feedback feeds back audio out-of-phase and creates a “hollower” type of sound, like a resonant tube. CROSS-FEEDBACK Modulation effects vary the delay time around a particular initial delay time, usually specified in milliseconds. Shorter delay times (0–15ms) are common with flanging, longer delay times (10–20ms) with chorusing. Attempting to change this value in real time often causes zippering, so it’s generally a set-and-forget parameter. VOICES Also called LFO Speed or LFO Frequency. The Rate sets the frequency of the modulation LFO. Typically, faster rates are used for chorusing, and slower ones for flanging. MODULATION LFO PHASE With stereo effects, this feature feeds back audio from one channel to the other channel’s input. This can create a more complex effect than simply feeding back the output of one channel to its own input. Feedback and Cross-Feedback can sometimes both be present. DAMPING Some chorusing processors have several delay lines, each with its own set of controls. This can create a more complex, evolving sound compared to using a single delay line. Each set of delay lines and controls is called a voice. Chorus units typically have 1, 2, 4, or 8 voices. PAN In modulation effects with multiple voices, you’ll generally find a Pan control for each voice to place it as desired in the stereo field. MODULATION SOURCE Choruses with multiple voices often have multiple LFOs (even a stereo chorus might have one LFO for each channel), and the Phase parameter varies the phase between the LFOs. Example: You might set two LFOs 180 degrees out of phase to modulate the channels in an equal and opposite manner. Increasing phase tends to increase the apparent stereo field width, as there’s less correlation between the right and left channels. MODULATION LFO RATE TEMPO SYNC Also called High Cut, Rolloff, etc. This inserts a filter in the feedback path that reduces high frequencies, creating a somewhat more subdued feedback sound. Additional filtering may be available to tailor the low and mid frequencies as well. BALANCE (WET/DRY MIX) There are many possible modulation sources. An LFO provides a cyclic change at a particular (usually slow) rate. Other sources include envelope follower (tracks the dynamics of the input signal), footpedal, MIDI continuous controller, etc. MODULATION DEPTH LFOs can usually be either free-running (the frequency is fixed at a user-set rate) or in the case of a software plug-in (or hardware unit with MIDI input), sync to the tempo of a host program or master clock. Tempo sync values are expressed as rhythmic values (1/4 note, 1/8 note, 1/8 note triplet, dotted 1/2 note, etc.). MODULATION SMOOTHING Sets the ratio of processed to unprocessed sound. Typically with flanging, these are mixed equally to provide the most dramatic flanging effect. With chorusing, the delayed signal is often mixed a bit lower than the dry signal to prevent the chorus effect from “taking over.” When set for wet sound only, it may be possible to obtain vibrato effects by shifting pitch cyclically without mixing it with the dry signal. MIX PHASE 44 EQ SEPTEMBER 2008 www.eqmag.com Cut Along Dotted Line Also called Modulation Width. This sets the difference between the minimum and maximum delay time. With chorusing, this is usually a relatively small difference, such as between 12 and 15ms. Flanging covers a much wider range, such as 0–15ms. High depth settings coupled with high rate settings tend to give a “warped record” effect, with unwanted pitch changes. Either lower the depth, or slow the rate. This provides a mathematical integration of the LFO waveform (rough translation: it rounds off square edges). It’s used mainly with a random waveform to change the standard “stairstep” shape into a smoother curve, thus producing smoother delay time changes. FEEDBACK In addition to feedback phase, a flanger might have a Mix Phase switch that allows throwing the wet signal out-of-phase. This produces a different type of tonality for flanging and to a less extent, chorusing. THROUGH-ZERO FLANGING Sends audio from the output back to the input, creating a more resonant sound. There may be separate feedback controls for each channel or voice. Also called Tape mode. With throughzero flanging, the delayed sound is mixed with a very slightly delayed dry sound. This allows the delayed signal to pass through a point where there is zero delay time between the dry and processed signals. http://www.eqmag.com

Table of Contents Feed for the Digital Edition of EQ Magazine - September 2008

EQ Magazine - September 2008 Contents Talk Box Sounding Board Punch In Freak Folk Todd Rundgren Guitar Trax Bass Management Key Issues Drum Heads Vocal Cords Mix Bus Cheat Sheet Sony Acid 6 Ableton Live 7 Portable Recorder Showdown Gadgets and Goodies Sounds Room with a Vu

EQ Magazine - September 2008

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