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Tremolo Effect

Module by: Ed Doering. E-mail the authorEdited By: Erik Luther, Sam Shearman

Summary: Tremolo is a type of low-frequency amplitude modulation. Learn about the vibraphone, a mallet-type percussion instrument that can create tremolo, experiment with the tremolo effect using an interactive LabVIEW VI, and learn how to model the tremolo effect mathematically.

Table 1
LabVIEWq.png This module refers to LabVIEW, a software development environment that features a graphical programming language. Please see the LabVIEW QuickStart Guide module for tutorials and documentation that will help you:
• Apply LabVIEW to Audio Signal Processing
• Get started with LabVIEW
• Obtain a fully-functional evaluation edition of LabVIEW

Overview

Tremolo is a type of low-frequency amplitude modulation. After learning about the vibraphone, a mallet-type percussion instrument that creates tremolo, experiment with the tremolo effect using an interactive LabVIEW VI and learn how to model the tremolo effect mathematically.

Physical Tremolo: Vibraphone

The vibraphone is a mallet-type percussion instrument similar to the xylophone and marimba. The percussionist in the right foreground of Figure 1 is playing a vibraphone.

Figure 1: Vibraphone (right foreground); click for larger version. Photographer: Charles Dietlein (http://www.flickr.com/photos/dietlein/232084492/). Copyright holder has granted permission to display this image under the Creative Commons Attribution-NonCommercial-NoDerivs license.
Figure 1 (232084492_4d55954909_b.jpg)

Following are the vibraphone's key characteristics:

  • Range of three octaves, beginning on F3 (the F below middle C)
  • Playing surface is covered by metal bars; the pitch of each bar increases as the length decreases; bars are typically struck by soft cord- or yarn-covered mallets
  • Sound intensity is increased by placing a series of resonating tubes (resonators) directly under each bar
  • Sustain pedal controls whether or not a damper is applied to the metal bars, giving the vibraphonist similar expressive control as a piano
  • Motor-driven disks rotate between the metal bars and resonators cause sound intensity to fluctuate (tremolo effect)

The name "vibraphone" was originally derived from the term "vibrato," since the undulating sound of a vibraphone resembles that of a vocalist singing a long note with vibrato. However, vibrato refers to a low-frequency fluctuation in frequency, an altogether different effect (see Vibrato Effect for details).

Tremolo Demonstration

LabVIEW.png Download and run the LabVIEW VI tremolo_demo.vi, which demonstrates the tremolo effect applied to a sinusoidal oscillator. Tremolo normally requires two controls: rate determines how quickly the amplitude should fluctuate, and depth establishes the amount of amplitude fluctuation. The third control adjusts the pitch of the sinusoidal oscillator.

Modeling the Tremolo Effect

Tremolo is a type of low-frequency amplitude modulation. The screencast video of Figure 2 develops the mathematical equations needed to model the tremolo effect. After watching the video, try the exercises below to ensure that you understand the main concepts.

Figure 2: [video] Develop the mathematical equations needed to model the tremolo effect
Figure 2 (lfmod_tremolo-eqn.html)

Exercise 1

What is the name of the term f R f R ?

Solution

Rate

Exercise 2

Which ratio is the basis of depth when expressed in decibels (dB)?

Solution

Ratio of maximum to minimum loudness

Exercise 3

True/False: Tremolo rate is typically above 20 Hz.

Solution

False; tremolo rate is typically between 3 and 10 Hz

Exercise 4

Which modification to the basic envelope equation is required to avoid clipping?

Solution

Subtract the depth value D

Now that you have been introduced to the main concepts of the tremolo effect, return to the interactive VI of the previous section. Experiment with the depth and rate controls, and confirm that the typical values mentioned in the screencast video in Figure 2 seem reasonable.

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Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

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