Reaper is filled with lots of handy features that sit around in its assortment of menus. And one of these is Plug-in Parameter Modulation. This allows you to modulate a parameter on any of your plugins. This gives you great control over your tracks and plugins, plus allows you to add movement and interest to your tracks through the modulation. Let's see how this is done.
Step 1 '" Choose an Effect
On a track, click on the FX button to bring up the Add FX dialog box. Choose a plug-in to add to the track. I'm going to be using the ReaEQ. But you can add any plug-in and follow along.
On the EQ, set the first band to a high-shelf. Set the Frequency to about 15 kHz and the Gain to -34dB. Set the bandwidth to about 0.17. Also give a slight boost with band 4.
I would like the band 1 Frequency to sweep up and down the frequency range to create a filter effect. This can be done with Parameter Modulation.
Step 2 '" Enabling Parameter Modulation
On your track click on the Trim button. Scroll down to the effect you want to modulate. I'll be working with the 1st frequency band with the ReaEQ. So on the 1-Freq (High), tick the Mod box.
This will bring up the Parameter Modulation dialog box. By default the Enable parameter modulation is ticked. This will determine the baseline amount of modulation that is applied.
Let's first test this out using an Audio Control signal as a modulation source.
Step 3 '" Using the Audio Control Signal
With Audio Control signal ticked, go under the track audio channel and choose 1+2. I'll be using these as the audio track source, you can set it to other tracks. Leave the direction set to positive, but you do have the option to change the direction to negative and centered.
The right display box will show you how much audio control signal modulation is applied. Using your mouse you can change the shape of the audio signal, hence changing the way the audio control modulation is applied.
Play back your track and start bringing up the baseline to about 80%. Set the attack to 227 ms and the Release to 290 ms. Bring the Min Volume down to -42 dB. You will now see some modulation happening in the Audio control signal shaping window. The green lines represent the modulation changes. Now bring the baseline down to about 50%. You will hear more modulation occurring. Drop it down to 20% and even more modulation occurs. Tweak the Min and Max Volume settings, these will change the modulation control over the frequency parameter. If you view the ReaEQ while the track is playing back, you will see on the plug-in how the parameter is being modulation. So as a suggestion, have the plugin UI and the Parameter Modulation window open at the same time so you can see how the parameter is being affected.
Step 4 '" Using the LFO
Now let's test out the LFO in The Parameter Modulation window. Untick the Audio Control Signal and now tick the LFO. This low frequency oscillator will now modulate the ReaEQ high-shelf band. You can choose a different waveshape.
Try these out. I'll stick with the Sine waveshape as it applies smooth modulation transitions. The random waveshape works really nice to introduce randomization into your modulation and sound sources. The speed of the LFO is in Hz, or you can change it to sync to the tempo (by ticking the Tempo Sync box). This will be now measured in beats. So 0.5 will be at half the beat, 0.25 at a quarter of the tempo, and so on'