Original article: http://www.soundonsound.com/sos/apr04/articles/synthsecrets.htm
When synthesizing sounds, the effects you place after your synth's output are often as important as the synth itself (just think of last month's Leslie). As we near the end of Synth Secrets, we consider how a digital effects processor works. This is the 60th article in a 63-part series. Read all parts.
Gordon Reid
Last month, as part of the final push to synthesize the effects of the Leslie rotary speaker, I introduced the bucket-brigade device (or BBD) delay line and showed how we could attempt to use this to assist the simulation. I then showed that, while possible, this was not practical. In fact, because of space considerations, I omitted a number of secondary factors that make analogue recreations of the Leslie less than satisfactory. For example, the spatial amplitude response of the horn assembly is not smooth, so the volume of the sound 'wobbles' as lobes of loudness and quietness rotate past your ears. What's more, this response is frequency-dependent, meaning that there are independent amplitude modulations occurring for each frequency in the signal. Then there's the bass rotor... Due to its limited size, this is not effective at frequency-modulating low-frequency signal components so, unlike the horn, it is more a source of amplitude modulation ('tremolo') than frequency modulation.
Figure 1: A simple eight-stage bucket-brigade device (or BBD) delay line.
Figure 1: A simple eight-stage bucket-brigade device (or BBD) delay line.