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FL Studio's mixer has four dedicated send tracks as well as the ability to use any other track as a send. This is fine for most purposes, but forces you to burn a track if you want to process a signal separate from the regular (i.e., not sent) audio before routing it to a send. With Patcher, you can process and send audio without using up any extra mixer tracks.
In this tutorial, we will be EQing an audio signal before routing it to a send track. This is useful if you want to control the timbre of each signal going to a reverb plugin, as opposed to setting up an EQ on the send track directly before the reverb plugin. For example, we can cut out the low end of a kick drum before sending it to the reverb so that the reverb will only respond to the higher frequencies of the kick drum, but can still respond to lower frequencies sent from other sources, like a vocal.
Route the audio you wish to use to a new mixer track, if you haven't already. Now, you will have to decide which mixer track to use a send. If you want to use one of the four dedicated send tracks, everything is already set up for you. To use a different mixer track for the send track, make sure the track your audio is routed to is selected, right click the track send button underneath your desired send track and select "Sidechain to this track". It would also be a good idea to name this track appropriately, by selecting it and pressing F2.
Back in the original mixer track, create an instance of Patcher in one of the effect slots. In Patcher, drag a connection between the 'Audio Input' node of the 'From FL Studio' object to the 'Audio Ouput' node of the 'To FL Studio' object. This lets a dry, unaffected, unsent audio signal pass on right through, as if Patcher wasn't even there.
Still in Patcher, right-click the 'To FL Studio' object and open the 'Audio' section of the 'Inputs' menu. This displays a list of all the mixer tracks Patcher can send audio to. All of the dedicated send tracks and any tracks we've 'sidechained' to will show up here. Choose whichever send track you want to use; I'm going to use the one I made in the first step, named 'Send'.
Right-click the background of Patcher and select an EQ plugin from the 'Add plugin' menu. The Fruity Parametric EQ 2 will be fine. Connect the audio input node of the EQ (located on the left side) to the 'Audio input' node of the 'From FL Studio' object. Connect the audio output node of the EQ to the newly created 'Send' node on the 'To FL Studio' object. Now our audio goes through the EQ before going to the send track.
A send is useless if it doesn't actually do anything, so select whichever mixer track you're using as a send and insert a reverb plugin in one of the effect slots. the Fruity Reeverb 2 plugin will work fine. Open the reverb plugin and change the wet/dry mix level to 100% wet. In Fruity Reeverb 2, this is done with the sliders on the right side. Drag the 'Dry' slider all the way down and middle-click the 'Wet' slider or right-click it and select 'Reset' from the menu.
Back in Patcher, double-click the EQ plugin to open the plugin's interface in the editors tab and adjust it to give the response you desire. I'm going to set the first band to a highpass filter and get rid of all the low frequencies. Since the Fruity Parametric EQ 2 has a level control, it could be used to set the send level. Otherwise, go to the map tab and click and drag along the connection between the EQ plugin and the Send node to set the send level.
That's pretty much it. All you have to do is tweak the reverb, EQ and send level until it sounds good. Here are some examples, with a kick drum.
First, without the EQ:
And then with the EQ: