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In The Studio: Audio Effects Explained (Includes Audio Samples)
Starting with a variety of modulation effects and moving along to a whole lot more...
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This article is provided by Audio Geek Zine.

 
A while ago I mentioned using modulation effects to help create movement within a mix. Here, I’ll explain the different types of modulation effects that we have available for mixing, and then move along to gates, compression, EQ, delay, reverb, de-essing, and a whole lot more.

The modulation effects I’ll be discussing include:

—Tremolo
—Vibrato
—Flanging
—Phasing or Phase Shifting
—Chorus

I’ll start with some easy ones then move on to the harder to explain—but more commonly used—effects.

All of them are built around a low-frequency oscillator, more commonly referred to as just an LFO. An LFO is an audio signal usually less than 20 Hz that creates a pulsating rhythm rather than an audible tone.

These are used for manipulate synthesizer tones, and as you will see, to create various modulation effects. All of the effects listed use sine wave as the wave shape for the LFO.

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Tremolo is an effect where the LFO is modulating the volume of a signal. The signal attenuation amount is controlled by the depth and the rate adjusts the speed of the LFO cycles.

Listen to an example of Tremolo

Vibrato is an effect where the LFO is modulating the pitch of a signal. This is accomplished by delaying the incoming sound and changing the delay time continually. The effect usually not mixed in with the dry signal. The depth control adjusts the maximum delay time, and rate controls the lfo cycle.

Listen to an example of Vibrato

Flanging is created by mixing a signal with a slightly delayed copy of itself, where the length of the delay is constantly changing. Historically this was accomplished by recording the same sound to two tape machines, playing them back at the same time while pushing down lightly on one of the reels, slowing down one side. The edge of a reel of tape is called the flange, hence the name of the effect.

These days we accomplish the same effect in a much less mechanical way. Essentially the signal is split, one part gets delayed and a low frequency oscillator keeps the delay time constantly changing. Combining the delayed signal with the original signal results in comb filtering, notches in the frequency spectrum where the signal is out of phase.

We usually have depth and rate controls. The depth controls how much of the delayed signal is added to the original, and the rate controls how fast it will change.

Phasing (or phase shifting) is a similar effect to flanging, but is accomplished in a much different way. Phasers split the signal - one part goes through an all-pass filter then into an LFO, and is then recombined with the original sound.

An all-pass filter lets all frequencies through without attenuation, but inverts the phase of various frequencies. It actually is delaying the signal, but not all of it at the same time. This time the LFO changes which frequencies are effected.

Phase shifters have two main parameters: Sweep Depth, which is how far the notches sweep up and down the frequency range; and Speed or Rate, which is how many times the notches are swept up and down per second.

Listen to an example of Phasing

Chorus is created in nearly the same way as Flanging, the main difference is that Chorus uses a longer delay time, somewhere between 20-30 ms, compared to Flanging which is 1-10 ms. It doesn’t have the same sort of sweeping characteristic that Flanging has, instead is effects the pitch.

Again the LFO is controlling the delay time. The depth control affects how much the total delay time changes over time. Changing the delay time up and down results in slight pitch shifting.

Listen to an example of Chorus

You may have noticed that the majority of effects here involve delay. You can recreate most of the effects by using a digital delay with rate and depth controls, such as the Avid ModDelay2.


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