Modulation
Modulation
We have discussed the most common modulation effects such as chorus, flanging and phasing. Now it is time to investigate other modulation effects.
Ring Modulator and Frequency Shifter
These two related effects are based on modulation of the signal amplitude. Both effects were popular during the 1970s and are currently experiencing something of a renaissance. The ring modulator, for example, was extensively used on jazz-rock and fusion records in the early 70s. The frequency shifter was, and still is, found as part of many modular synthesizer systems. Due to the intricate nature of its hardware, the frequency shifter was (and remains) relatively expensive to produce, and was therefore never as widespread as the simpler ring modulator.
The ring modulator modulates the amplitude of the audio input signal using either the internal oscillator or a second audio signal. The frequency spectrum of the resulting effect signal equals the sum of, as well as the difference in frequency between the two original signals. For example, if you were to put in two sine tones at 500Hz and 600Hz, the output would comprise tones at 1100Hz and 100Hz. Conversely, feeding the same 500Hz tone into both inputs would produce components at 0Hz (a silent DC offset) and at 1000Hz (an octave up from the pitch at the inputs). However, the results are only as simple as this when you input pure tones. When sounds rich in harmonics are used, all those harmonics contribute to the sum-and-difference process. This result is an output that is very complex harmonically.
The frequency shifter hosts an elaborate array of all-pass
filters that enable to separate the sum-and-difference signals into two separate audio signals. One carries the audio signal with its frequency spectrum shifted up, the other with its spectrum shifted down. The amount of frequency shift is set via the frequency of the internal sine wave oscillator.
Frequency shifting should not be confused with pitch shifting. Pitch shifting transposes the original signal, leaving its harmonic frequency relationship intact. The frequency shifter shifts the frequency content by a fixed amount and, in doing so, alters the frequency relationship of the original harmonics. The resulting sounds range from sweet and spacious phasing effects to strange robotic timbres.
The Ringshifter (above) can be found within Logic Pro and is a plug-in that emulates both a ring modulator and frequency shifter. It can operate with one input (using the internal sine wave to modulate), or you can include a second input using the side chain in Logic.
Because of the way in which the output frequencies are generated, ring modulators generally produce atonal, non- musical sounds. This has made them popular for science- fiction special effects, but they can also be used musically, with a little care.
For example, if two similarly pitched synth patches are ring- modulated together then, providing the input waveforms are not too harmonically complex, the output can be both interesting and musically useful. Some non-harmonic components will almost certainly still be present, and detuning the two inputs by a very small amount can produce unusual low-frequency beating effects, but you can arrive at some very worthwhile sounds in this way.
If you find ring modulation a little too strident for you, it can often be made more palatable by blending some of the original unprocessed input in with the processor’s output. If you’re still a bit cagey about using this effect, then perhaps the safest tactic is to use it as a sound design technique, sampling any isolated moments for later use – ring modulating a 100Hz tone with a vocal to produce the familiar Dalek voice is always fun, at least!
Processing percussion via a ring modulator can be good – use a pitched synth sound for the other input and you’ll end up with a metallic, pitched drum part that could form the basis of an experimental electronic song or dance track. Ring-modulating different cymbal sounds together is also an interesting experiment, which creates new, electronic- sounding cymbals.
If you want to create new sounds and treatments based upon a basic ring-modulation sound, try combining it with other effects. For example, use a dry sound as one input to the ring modulator, and its reverb or delay as the other. You can also further process the ring modulator output using conventional but dramatic effects such as flanging or heavy delay.
Leslie Cabinet and Simulation
The Leslie speaker is a specially constructed loudspeaker used to create special audio effects. Named after its inventor, Don Leslie, it is particularly associated with the Hammond organ. Separate Leslie speakers were a “must have” accessory for all Hammond owners, particularly after its characteristic sound was popularised by such acts as Procul Harum on A Whiter Shade of Pale, or the Spencer Davis Group on Gimme Some Loving.
The Leslie speaker consists of two driver units: a treble unit with horns, and a bass unit. The key feature is that the horns of the treble unit and a sound baffle for the bass unit are rapidly rotated using electric motors to create ‘Doppler effect-based’ vibrato, tremolo and chorus effects. It can be switched between its two speeds, and the transition between the two produces the most characteristic effects.
The resulting sound is instantly identifiable as that of the Hammond organ, frequently heard on psychedelic and rock music of the 1960s and 1970s. Unlike a high fidelity loudspeaker, the Leslie is specifically designed, via reproduction of the Doppler Effect, to alter or modify sound; faithful reproduction has never been part of its appeal. Much of the unique tone is owed to the fact that the system is at least partially enclosed, but with linear louvers along the sides and front so that the unit can vent the sound from within the box after the sound has bounced around inside, mellowing it
The Leslie might be considered an electro-mechanical sonic effects machine. Many rock and roll organists have turned the box around to expose the horn’s rotation for a visual effect, and in the hope of projecting a more powerful sound from both speakers.
While normally used with the Hammond organ, because it is a separate unit, any musical source, such as an electric guitar, can be played back through a Leslie speaker, creating a wide range of surprising and dramatic effects. John Lennon’s voice was processed through a Leslie speaker for the highly experimental song “Tomorrow Never Knows” on The Beatles’ 1966 album Revolver.
The classic Leslie is still made and sold to this day, though similar effects can now be obtained via analog electronic devices and digital emulation. Chorus and phase shifter devices can mimic the sounds produced by a Leslie speaker. In fact, early phase shifters like the Uni-Vibe were specifically marketed as low-cost Leslie substitutes for guitarists and used a foot-operated fast/slow switch. There are some convincing Leslie simulation plug-ins, such as the native instruments B4 (B3 Hammond organ simulation and Leslie plug-in).
Like the phasing effect, Leslie effects tend to work better with slower material. It works great on acoustic and electric guitar, but also on vocals, drums, etc.
When using a plug-in simulation, you can insert it across the channel you want to process. If you want a more subtle effect, you could have the direct signal more prominent in the mix, and feed the Leslie effect from aux sends, so you can bring in the Leslie sound, pretty much like a reverb. This can work well with vocals, for example.
Panner
A panner is simply a device that automatically pans a mono signal from left to right and back again, usually under the control of an LFO. It is closely related to tremolo, an effect created by modulating the level of a signal using an LFO, except that in the case of the panner there are two modulating circuits, one of which is at maximum gain while the other is at minimum. Some effect units incorporate options for triggering the pan to MIDI notes or syncing it to tempo via MIDI Clock, in which case it’s possible to synchronise the panning to the tempo of the music.
While panning raw sounds all over the place can sound a little dated if you overdo it, it can be effective to leave the original sound where it is and just pan the reverb or delay element of the sound. As well feeding the panner from auxes, you can bring the panner into the mix more subtly.
A more recent advance is three-dimensional panning, an effect that combines left/right panning with psycho- acoustic front/back panning. Continually changing levels and EQ changes make the signal sound as though it’s moving in a circle in front of the listener rather than simply following a straight line. As the sound pans, it seems alternately closer to the listener, then further away.
As mentioned above, panning can work well on effects such as delay and reverb, but also works well with effect- type sounds in your mix (like transition-type effects), and with synths. Note that with a DAW, mixers have pan with automation, so you can use this to create some movement.
