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We've gotten a lot done with delay so far using the parameters of level, delay time, feedback, low-pass filtering, and polarity reversal. It's time to take it to the next level using what are known as modulation controls. Modulation is simply a secret codeword for change. We want to introduce a way for the delay time to fluctuate during the song. The delay effects we've discussed so far, echo for emphasis, echo for groove, and slap back echo, use only a static delay. Interesting new effects can be built on a changing delay time.
And while we might manually change the delay time ourselves, a recorder delay time changes into the mix automation system. It is really useful to have the delay processor itself introduce the change. And this is done using a simple low-frequency oscillator or LFO. The LFO is an oscillating waveform that drives the delay time parameter. We don't listen to this signal. Instead, the delay time is controlled by it. If the LFO is a slowly moving sine wave, then the delay time parameter will sweep slowly with a sine wave trajectory through a range of delay times.
If the LFO is a quickly moving sawtooth wave, then the delay time changes more quickly in a sawtooth pattern. The LFO has three simple properties, rate, depth, and shape. Rate is the frequency of the LFO. Remember, we aren't listening to this signal. It's only used to change the delay time parameter in our delay processor. Rate specifies whether the manipulation of the delay time will be slow, quick, or somewhere in between. Depth is the amplitude of the LFO. It determines the amount of change to the delay time.
Do we modulate that delay by 5 milliseconds, 50 milliseconds, 500 milliseconds or more? Shape is the waveform of the LFO. A sine wave is common. It changes the delay time in a regular sine wave pattern through the range of delay values you specified using depth, doing so as quickly as you specified using rate. But a sine wave is not the only choice. The delay changing trajectory might follow any standard waveform, sawtooth, triangle, and square waves are common LFO shapes.
And maybe most interesting of all, many delay processors let you select a random wave shape so that the delay time moves without the regular pattern of the more structured, repeating wave shapes. This can lead to a more organic form of modulating delay. Mastering the modulation section of your delay by understanding these LFO building blocks, opens the door to a variety of new delay effects, doubling, chorus, spreaders, thickeners, and flanging are all built on changing delays as we discuss in the upcoming videos.
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