Reverberation

Introduction

Reverberation is a property of concert halls that greatly adds to the enjoyment of a musical performance. The on-stage performer generates sound waves that propagate directly to the listener's ear. However, sound wavesalso bounce off the floor, walls, ceiling, and back wall of the stage, creating myriad copies of the direct sound that are time-delayed and reduced in intensity.

In this module, learn about the concept of reverberation in more detail and ways to emulate reverberation using a digital filter structure known as a comb filter .

The screencast video continues the discussion by visualizing the sound paths in a reverberant environment. The impulse response of the reverberant environment is also introduced. Understanding the desired impulse response is the first step toward emulating reverberation with a digital filter.

Comb filter theory

The comb filter is a relatively simple digital filter structure based on a delay line and feedback . Watch the screencast video to learn how you can develop the comb filter structure by considering an idealized version of the impulseresponse of a reverberant environment.

The difference equation of the comb filter is required in order to implement the filter in LabVIEW. In general, a difference equation states the filter output y(n) as a function of the past and present input values as wellas past output values.

Take some time now to derive the comb filter difference equation as requested by the following exercise.

Comb filter implementation

Once the difference equation is available, you can apply the coefficients of the equation to the LabVIEW "IIR" (infinite impulse response) digital filter. The screencast video walks through the complete process you need to convert the comb filter difference equation into a LabVIEW VI. The LabVIEW MathScript node creates the coefficient vectors. Once the comb filter is complete, its impulse response is explored for different values of delay line length and feedback gain.