Build A Simple Synth In Reaktor, Part 3

Many programs exist for creating your own instruments, from Logic Pro to MAX/MSP. Few, however, are as musically immediate and satisfying as NI's Reaktor. Toby Pitman gets synth building!  

Last time we added a bit of Pulse Width Modulation to our oscillator via an LFO. In this final part we’re going to add the LFO to our filter. Here’s where we left off.

The story so far...


Currently we have a separate envelope controlling our filter. We can choose the amount of envelope by using the pre-existing ENV control built in to the Multimode Filter macro. We need to somehow merge our LFO with this envelope information. To do this we need to customize our filter macro. Let’s have a look!


Step 1 - Enter The Filter!

Inside the Structure View double-click on the Multimode Filter macro.

Multimode Filter macro


Inside you’ll see the structure of the filter. Scary! This is a bit more complex than our previous macro structures. At the end of the day Reaktor is all about signal path. All we have to do is work out what we need to change.

The filter's structure


Step 2 - Disconnect The Envelope 

As we need to merge our LFO with our envelope we need to find where the envelope is coming in. You can see the port and envelope amount modules here.

The port and envelope amount modules


Essentially we need to disconnect these to start with. Select the Multiply module.

The Multiply module


...and delete it.

Deleting the Multiply module


Step 3 - Create The LFO Ins

Create a new Port. Control-Click the Structure View and choose Built-In Module > Terminal > In Port. Name the port LFO.

LFO port


Create a new Knob by choosing Built-In Module > Panel > Knob. And set the parameters in the Function panel. Name it LFO.

LFO knob parameter


Step 4 - Blend The Modulation

We’re going to blend the modulation sources using a simple mixer. Choose Built-In Module > Signal Path > Amp/Mixer

Amp/mixer


Here it is. You’ll notice it only has one input!

Amp/mixer input


First up connect the Env port to the in of the mixer.

Env port to the in of the mixer


To create another input hold Command (or Control on a PC) and drag a cable towards the three dots above the green stripe.

creating another amp/mixer input


When you hover over them a new channel is created.

new channel


Step 4 - Convert The Amount Signals

Now this may seem weird using an audio mixer to blend modulation data but it works. All we need to do is convert our knobs to the right kind of data to control the blend.

Because the mixer works in Logarithmic values we need to convert our knobs output values from Linear to Logarithmic. We do this using the Log. (A) module. Don’t ask!!!

Choose Built-In Module > Math > Log. (A). 

Log. (A) module


Place a Log. (A) module between the Knobs for Env and LFO and cable to the Level ports.

Log. (A) module cabling


Step 4 - Convert The Signals Back To Events

Now we need to convert the signal coming out of the mixer from an Audio type to an Event type. We do this with the A to E module. Choose Built-In Module > Auxiliary > A to E.

A to E module


This type of conversion from audio data to event data is pretty common in Reaktor. Wire the output of the mixer to the new module.

output of the mixer cabled into the A to E module


Now hold Command (or Control on a PC) again and drag the output to the Add module to create a new input.

dragging the output to the Add module


Step 5 - Hook Up The LFO

Now go back to the Instrument structure and connect the LFO to the LFO port on the filter.

connecting the LFO to the filter's LFO port


Using the Edit Panel button move your LFO knob into position.

moving the LFO knob


You should now be able to blend the Filter Envelope and the LFO together. Here’s what it sounds like.


And there you have a simple subtractive synth. Hope this opened some avenues to explore Reaktor. Have fun!

For the past 20 years Toby has worked as a professional guitarist, programmer and producer. Clients include Sir Paul McCartney, George Michael, Shirley Bassey, Yusuf Islam, Giles Martin as well as the London 2012 Olympic Ceremonies. He has also worked extensively in TV, Advertising and Film. As well as composing himself he has also ... Read More

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