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  • All About Synthesizer “Hard Sync”

    By Anderton |

    The more interesting the synth sound, the better


    By Craig Anderton


    One of the great advantages of virtual instruments is that many parameters are automatable, so you can introduce dynamic changes as you do with other elements of a mix. But which parameters are worth automating? Just about everyone appreciates twisting filter cutoff frequency and envelope attack or decay, but today’s virtual synths have seemingly progressed faster than the ability of musicians to assimilate all the cool new tricks they can do. Case in point: oscillators.


    If you think that oscillators are simply static tone generators that are good only for providing a signal so that filters and envelopes can do something interesting to them, think again—thanks to capabilities like hard sync, frequency modulation, and ring modulation. These are powerful options that can make a synth leap out of a track by adding a more dynamic, edgy timbre. Let’s take a look at hard sync, the most popular of these effects, and a trademark sound of old school analog synths.




    One of the best known-examples of the hard sync sound appears in the synth figure on that old 80s hit by the Cars, “Let’s Go.” Hard sync changes a tone’s harmonic structure, so it’s kind of like filtering; but the sound is more pronounced, with an almost vocal-type resonance.


    Hard sync requires two oscillators. One oscillator tracks the keyboard and sets the pitch. However, we never hear this oscillator’s audio. Instead, it provides a sync reference for a slave oscillator, whose period (the length of one cycle) is always forced to be the same as the pitch oscillator. This is why it’s considered “synched” to the pitch oscillator.


    Confused? Here’s a more obvious example of “hard sync,” but at a much lower frequency. Suppose you have a slow LFO hooked up to control filter cutoff. There will probably be a mode that re-triggers the LFO when you hit a key. This “hard syncs” the LFO to your playing: no matter where the LFO is in its cycle, when you hit a key, it re-starts.


    Similarly, regardless of what the slave waveform is doing, when the pitch oscillator starts a new cycle, so does the slave. If you change the slave’s pitch, the waveform will still have the same period—thus the same perceived pitch—because it’s slaved to the pitch oscillator (Fig. 1). However, the harmonic structure will change radically as the slave’s frequency changes.





    Fig. 1: These three waveforms represent three different slave oscillator frequencies, but the pitch oscillator frequency is the same in each case. Note that the period (the length of each waveform’s cycle) is the same, but the waveform’s shape—and therefore, harmonic structure—differs.


    There are a few “rules” about hard sync settings:


    • You generally don’t want any audio from the pitch oscillator. Listen to the output from the slave oscillator.
    • If the slave oscillator pitch goes lower than the pitch oscillator, then the hard sync effect disappears. The slave oscillator should always be higher-pitched than the pitch oscillator.
    • The pitch oscillator waveform isn’t really significant, as it’s used only as a timing reference. The slave oscillator waveform is less important than usual because the hard synching action has such a strong effect on the sound. However, a sawtooth or square wave will give more “bite” than a sine or triangle wave.




    In addition to setting up the oscillators, you also need a modulation source to vary the slave oscillator frequency. Common choices are an envelope generator, mod wheel, or LFO (particularly an LFO that’s reset when you play new notes). However, you need a really wide-range pitch sweep—like four or five octaves—to get dramatic hard sync effects, and many modulation sources aren’t really designed to deliver that kind of output.


    The simplest solution is to “double up” the number of envelope destinations. For example, if there are two possible output destinations, send both to the slave oscillator’s pitch, and turn up both output levels as high as possible. I’ve even set two envelope generators with the same settings, each with two outputs, to the slave pitch, thus quadrupling the range. Also, if the oscillator has a control input, make sure that it too is set for as wide a range as possible.


    Fig. 2 shows the setup for a typical hard sync patch using Cakewalk’s PSYN II synthesizer. Consult your particular soft synth’s documentation, because you want to make sure you know which oscillator is modulating which so you can listen to the slave oscillator.




    Fig. 2: In Cakewalk’s PSYN II synth, Osc I sets pitch; Osc II is the slave. The section outlined in red sets the two oscillators to sync mode. The yellow line outlines the slave’s pitch parameters, whose initial setting is higher than Osc I. The modulation source is an envelope generator decay (outlined in orange); it has two modulation outputs (blue outline), both set to control Pitch, and both set to maximum to sweep over the widest possible range. The slave’s envelope generator modulation sensitivity control (green outline) is also set to maximum.


    There are oscillator cross-modulation options other than hard sync; Frequency Modulation (FM) is also popular. In a nutshell, this causes one oscillator to modulate the other (without re-synching) so that the resulting signal has more complex sidebands. Increasing the level of the modulating signal increases the complexity of the signal.


    In any event, next time you need to do a cutting synth solo, don’t reach for the EQ or exciter processor: set up hard sync, link it to your mod wheel, play expressively, and record the mod wheel movements as automation. You’ll be treated to a far more animated, biting sound that if you let it, can take over a track.



       Craig Anderton is Editor Emeritus of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.


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