So far in Sweetwater’s Simple Guide to Modulation series, which provides a brief overview of how to begin using modulators to build exciting patches, we’ve tackled LFOs and envelope generators. Here, in the third part of this four-part series, we’ll dig into sample & hold (S/H). Perhaps the most esoteric modulator yet, it is known for creating random electronic bleeps and bloops straight out of 1960s and ’70s sci-fi films! But, in keeping with the “Simple Guide” theme, we’ll explore some real-world uses of sample & hold along with a quick discussion of how it works. We think you’ll agree that sample & hold is capable of a lot more than glitchy sonic chaos. When used in a musical context, sample & hold can manifest wonderfully textured sounds that can take your patch-design game to the next level!
How Does Sample & Hold Work?
Sample & hold can be one of the more challenging concepts for beginning synthesists to wrap their minds around. So, we’ll attempt to describe it in as unassuming terms as possible. The first thing to realize is that the name of the sample & hold circuit is quite literal. As Daniel Fisher discusses in Synth Clips episode 20 — “Sample & Hold and Random,” a typical sample & hold circuit has two inputs — a signal input that receives dynamic voltage and a gate input for receiving a trigger signal. And it samples and holds the incoming signal each time it receives a gate input.
If that’s already sounding too complicated, then think about it this way: When you press a key on an analog synthesizer, the sample & hold circuit goes to work, continuously snagging a small snippet of whatever signal is coursing through it at a user-defined rate and then repeating that signal until you hit the next key. Now, with most sample & hold–equipped synthesizers, you can choose which type of signal is sampled. For instance, you can sample a white- or pink-noise signal or a waveform generated by one or more of your synth’s oscillators or its LFO. And each type of signal will make your sample & hold behave in a distinctive way. Random signals, such as noise, will generate, well, random and chaotic sample & hold behavior! Meanwhile, standard waveshapes will generate more predictable, though still relatively random, behavior. Plus, like an envelope generator or an LFO, sample & hold is often assignable to several parameters. We’ll focus on modulating two of these parameters with sample & hold: pitch and filter cutoff.
The sound samples were created with the Arturia ARP 2600 V software synthesizer, which is available standalone or as part of Arturia’s outstanding V Collection 8 software instrument bundle. A strikingly accurate emulation of a classic semi-modular synth (complete with virtual patch cables!), the Arturia ARP 2600 V is an excellent instrument for learning synthesis.
So, let’s start modulating parameters — this time with sample & hold!
Modulating Pitch
Modulating pitch with sample & hold is the easiest way to hear the effect that sample & hold modulation has on a source. To keep things straightforward, we’re starting with a single oscillator producing a pulse wave and playing just two notes, twice each.
To illustrate the random and not-so-random behavior that can be achieved with sample & hold, listen to these clips that will demonstrate different waveforms, starting with those that produce the least predictable behavior (such as random noise) and moving to the waveforms that produce the most predictable behavior.
For our first clip, we’ll apply pink noise as the signal source for the Arturia ARP 2600 V’s sample & hold generator to create the iconic chaotic-computer sound often associated with sample & hold.
Next up, we’ll feed some white noise into the sample & hold circuit. Though it produces equally unpredictable results, it has a slightly different character due to the inherent differences between white and pink noise. To learn more about those differences, read “Pink Noise Versus White Noise” on inSync.
Let’s move on to using waveforms as a signal source. This is easily achieved on the Arturia ARP 2600 V by patching one of the available waveform outputs on OSC2 or OSC3 to the Noise Generator input on the sample & hold module.
Unlike using white or pink noise as a signal, when you apply a waveform to the sample & hold’s signal input, the results become slightly more predictable. Furthermore, each time you press a key, the sample & hold will alter its rate because it’s being fed a waveshape with a different frequency. Now, that might seem contradictory to the notion that using waveforms makes sample & hold more predictable. Yet, each key will produce a repeatable rate change, which you can learn and then apply to a musical context.
As always, this is easier to understand once you hear it. So, let’s give a listen to what happens when you patch a sine wave into the sample & hold circuit.
Still pretty crazy! But it’s definitely more controlled than either the pink or white noise, and it’s easy to discern when the two notes are being played by noting the change of the sample & hold rate.
A triangle wave gives us a similar sound with a higher degree of predictability.
The increased predictability is due to the triangle wave’s linear shape versus the sine wave’s exponential/logarithmic shape. We’re treading into some pretty nerdy territory here; but, put simply, a triangle wave is going to sound more pleasant and harmonious than the sine wave, and it will be easier to fit into a musical context.
Next, let’s use a sawtooth wave as our sample & hold signal source.
Here, things are starting to get very predictable. Although the notes being generated are atonal, they’re creating a fairly orderly descending pattern. If you want to create an ascending pattern, then just invert the sawtooth.
Finally, by selecting a pulse wave as the signal source, we get the most predictable and repetitive modulation of the bunch. Arguably, it is not as musical as the sawtooth when applied to pitch; however, using a pulse wave as your sample & hold signal is a fun way to experiment with percussive sounds and off-kilter rhythms.
Modulating Filter
As you can hear, there are plenty of cool uses for modulating pitch with sample & hold. Yet, if you’re like us, you might find yourself more often assigning sample & hold to the filter cutoff. In this way, you maintain the pitch of your synth lines, but you can benefit from a bit of random modulation to add interest to patches. As with the pitch examples, modulations will vary in degree of unpredictability depending on the signal sent to the sample & hold circuit.
In our first example, we’re using white noise, and we’ve dialed up a bit of resonance to highlight the movement of the modulation.
Next, we switch over to the sawtooth wave, and we’re treated to curious, rhythmic filtering that varies according to which key is struck.
For a cool reverse-envelope effect, select an inverted sawtooth wave as your sample & hold signal source.
Last, we fed a pulse wave into the sample & hold circuit. But, before doing so, we assigned a sine wave as a modulation source for the pulse width. This adds a touch more variation and life to the patch.
Putting It All Together
For the sake of putting theory into practice, we created a short musical piece that highlights the use of sample & hold. The track consists of three elements: drums created in the FXpansion BFD3 virtual acoustic-drum module, a bass line using two oscillators on the Arturia ARP 2600 V with manual filter-cutoff sweeps, and a melody line that significantly employs sample & hold on the filter cutoff fed with a reverse sawtooth wave from OSC2. Combined with a ping-pong delay and an algorithmic plate reverb, this part fills up a ton of sonic real estate. And the per-key variations contribute a lot of movement, forming a very dynamic part from just a few elements.
Conclusion
There you have it — a very simple guide to modulation with sample & hold. In this article, we just covered the basics, but sample & hold can be further manipulated for some seriously out-there results. Try it out during your next synth jam and see what sonic madness unfolds!
Check out the previous articles, too.
