DAFX: Digital Audio Effects, Second Edition

3.4 Applications

Several applications of modulation techniques for audio effects are presented in the literature [Dut98a, War98, Dis99]. We will now summarize some of these effects.

3.4.1 Vibrato

The cyclic variation of the pitch of the input signal is the basic application of the phase modulator described in the previous section. A detailed description can be found in Section 2.6.1.

3.4.2 Stereo Phaser

The application of a SSB modulator for a stereo phaser is described in [War98]. Figure 3.11 shows a SSB modulator performed by a recursive allpass implementation of a Hilbert filter. The phase difference of 90° is achieved through specially designed allpass filters.

Figure 3.11 Stereo phaser based on SSB modulation [War98].

3.4.3 Rotary Loudspeaker Effect

Introduction

The rotary loudspeaker effect was first used for the electronic reproduction of organ instruments. Figure 3.12 shows the configuration of a rotating bi-directional loudspeaker horn in front of a listener. The sound in the listener's ears is altered by the Doppler effect, the directional characteristic of the speakers and phase effects due to air turbulence. The Doppler effect raises and lowers the pitch according to the rotation speed. The directional characteristic of the opposite horn arrangement performs an intensity variation in the listener's ears. Both the pitch modification and the intensity variation are performed ...