Getting airy pad synth sounds is quite accessible for most people with a few plugins. But getting deep, rich, low-frequency ambience can be tricky. Learn how to achieve these sounds using sub-oscillators.
By DJ Pangburn
Getting light, airy ambient synths is relatively straightforward—the principle is the same whether you’re using hardware, software, analog or digital synthesizers. You filter out the lower frequencies, give the signal a long sustain and release, modulate some parameters with an LFO, then add some effects like delay, reverb, and chorus.
To get low ambient frequencies on the other hand, it can be a little more complicated. Sometimes it’s enough just to play an octave or two down the keyboard. But there is another tool in the synthesis arsenal for getting deep ambient sounds: the sub-oscillator. Typically, sub-oscillators are used to accent basslines by fattening up the patch’s other oscillator(s).
Sub-oscillators, however, aren’t usually the featured effect on an entire ambient synth track. Below, we will illustrate how to use a sub-oscillator to create rich, deep ambient sounds in combination with plugin effects like delay and reverb.
This is a great question, because a good number of synths don’t have this feature. In simple terms, a sub-oscillator is an oscillator that is one octave below the main oscillator pitch. The most common type is a sine wave sub-oscillator. Again, sub-oscillators are often used to give depth to or “fatten” the low end of a synthesizer’s sound. The reason the sine wave sub-oscillator is most common is that it is the easiest and cheapest type to implement.
Many classic analog synths like the Roland Juno 106 and SH-101 came with sub-oscillators, but the Korg Poly-Six also came equipped with one. It’s probably one reason why the SH-101, along with its filter, has that glorious detuned sound for techno basslines. A mere turn of a dedicated rotary knob or flip of a switch is all it typically takes to introduce the sub-oscillator signal into the synth’s signal chain.
Sub-oscillators can also come as square, triangle and pulsewidth waveforms. And just as sub-oscillators need not be limited to one waveform, they also needn’t be limited to just one octave. Some sub-oscillators allow users to detune by two, three, or more octaves.
Because soft synths offer more flexibility than most hardware synths, sub-oscillators are pretty common in VSTs. Indeed, most of the best soft synths out there will have a sub-oscillator feature, so it’s really a matter of finding out what specific sounds work best for you.
Waves’ Element 2.0, an analog style polyphonic synth plugin, brings sub-oscillator functionality to your synth’s signal. “Sub,” as the feature is known on Element, mixes in a triangle wave that is one octave below Oscillator 1.
In the audio clip below, we selected the preset “Boog Mass” in Element. From there, we filtered out some of the higher frequencies and added a bit of resonance, before dulling the attack a bit and giving the signal longer sustain and release. Next, we turned our attention to the Sub feature. To give the synth a good amount of depth, we cranked the Sub knob all the way to the right. (Note: The melody we play below is in the C1-D2 octave.)
To give it more ambience, like some of Aphex Twin’s ambient music (which has serious warmth on the low end), we added some reverb using Abbey Road Chambers. We used the preset Tape Wobble for a bit of that old school tape effect. We also pegged both the reverb and wet/dry to 50% in the mix section. On top of that, we set the reverb on Element to 79.3 and the chorus to 23.9, which give the sound even more atmosphere.
To demonstrate a soft synth with multiple sub-oscillators, we turned to Analog, Ableton Live’s virtual analog synthesizer. We followed a similar process as with Element, but with one notable difference: each of Analog’s two oscillators features a sub-oscillator, allowing us to add some thickness to the signal with multiple waveforms. The result is a rich ambient bass sound reminiscent of Brian Eno and Boards of Canada.
For Oscillator 1, we selected a Triangle wave sub-oscillator and set it to 100%. For Oscillator 2, we used a Sine wave sub-oscillator at 100%. Of course, one sub-oscillator will do, but two are twice as nice. Even though Analog and Element are soft synths, by enabling their sub-oscillators we can give them that creamy and warm depth most often associated with vintage analog synths like the Moog Model D. (Note: The melody we play below is in the C3-D4 octave.)
As above, this clip needed a bit more atmosphere. To do this, we used both Abbey Road Chambers and one of Ableton’s reverbs for the task.
Once again, we used Abbey Road Chambers’ Tape Wobble preset, with the reverb and wet/dry both set to 35% in the mix section. To add a longer reverb tail to the overall mix, we used Ableton’s Forest Floor set to 39% dry/wet with a decay time of 12.9 seconds. The result is that the soft synth starts to sound like some of Eno’s work, but also resembles the rich bass notes used by Vangelis with his Yamaha CS-80 on the Blade Runner score.
To demonstrate how to give your hardware analog synthesizer some deep, wide, and rich sub oscillator sounds, we’ll turn to the Moog Sub 37. Released in 2014, Moog’s paraphonic synthesizer features a dedicated sub-oscillator in its Mixer module.
The Sub 37’s sub-oscillator is engineered to always be tuned exactly one octave below Oscillator 1’s pitch. And while the Sub 37’s sub oscillator waveform is always a square wave, a level rotary knob allows users to push the level beyond unity, which gives the oscillator section what Moog calls “gentle filter distortion.”
Being a Moog analog synthesizer, the Sub 37 sounds great even without the richness of its sub-oscillator. But adding the sub-oscillator gives the Sub 37 added depth. (Note: We play the melody below in the C3-D4 octave.)
In the final audio clip below, we add to this depth with some reverb from both Abbey Road Chambers and Ableton’s Forest Floor. We also added some long delay times with Waves’ Manny Marroquin Delay. The result is something like Mark Pritchard’s magnificent tune “Where Do They Go, The Butterflies,” which is drenched in long reverb tails and delays.
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