Tremolo effect

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 is playing a vibraphone.

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

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 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.

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 seem reasonable.