Poly Grid - Additive Synth

Alright, now it’s getting exciting. We’re going to turn our subtractive synthesizer into an additive synthesizer. Additive synthesis means manually generating overtones using individual oscillators—much like how a pipe organ works, where different pipes create different harmonics.

Step 1: Add a Second Oscillator #

1. Drag another Saw Oscillator into the Grid and drop it onto the input connection of the filter.
2. Hold ALT while doing this to automatically insert a Mixer module between the oscillators and the filter. This way, both oscillators feed into the mixer, and the mixer’s output goes to the filter.
   • Pro Tip: If you’re unsure about keyboard shortcuts, check the bottom of Bitwig’s interface. It displays which keys you can hold for different connection options.

Now you have two oscillators feeding into the mixer.

Step 2: Adjust the Second Oscillator #

Currently, both oscillators are receiving the same pitch because their Precords are active. As a result, they are playing the same frequency.

1. You can leave the second oscillator as it is or detune it slightly for a thicker sound.
2. To start building an additive setup, change the Ratio of the second oscillator from 1:1 to 2:1.
   • This makes the second oscillator play at double the frequency of the first oscillator (the second harmonic).

Now you’re stacking the fundamental frequency and the first overtone, creating the beginnings of an additive synth.

Step 3: Add a Third Oscillator #

1. Drag a third Saw Oscillator into the Grid and connect it to the mixer.
2. Set the Ratio of this third oscillator to 3:1, so it plays three times the frequency of the input pitch (the third harmonic).

At this point:

• The first oscillator plays the fundamental frequency (1:1).
• The second oscillator plays the second harmonic (2:1).
• The third oscillator plays the third harmonic (3:1).

This creates a stacked sound based on the harmonic series.

Step 4: Why Use Sine Waves for Additive Synthesis? #

Traditionally, additive synthesis is done using sine waves, not saw waves. Sine waves are pure tones with no overtones, so you can build a precise harmonic series by stacking them. Saw waves, on the other hand, already have built-in overtones, which can lead to overly dense or muddy sounds when stacked.

For a more traditional additive synth:

• Replace the saw oscillators with Sine Oscillators (right-click each module and select Replace With > Sine Oscillator).
• Each sine oscillator will represent a specific harmonic, and you can control the levels of each harmonic precisely.
• Optional: Remove the Filter because we can control the overtones with the oscillators directly!

Step 5: Expand the Setup (Optional) #

You're not limited to three oscillators! Add as many as you like to generate higher harmonics.

• Keep in mind that the Mixer module in Bitwig has a maximum of eight inputs.
• If you need more, you can chain multiple mixers together by routing their outputs into another mixer.

Conclusion #

In this example, we’ve transformed our subtractive synth into a simple additive synth by stacking multiple oscillators, each playing specific harmonics of the fundamental frequency.

Additive synthesis gives you precise control over the harmonic structure of your sound. Even though we used saw waves here for simplicity, switching to sine waves is a more accurate way to create clean, harmonic sounds. From here, you can keep adding oscillators or start experimenting with modulations to expand your synth!

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