In this 3 part tutorial we will take a look at Reason's main mixer, "faithfully modeled after the famous SSL 9000k analog mixing desk", to demonstrate a technique pros use to make their mixes pop. There is a reason the SSL 9000k has so many mix channels. Often a single instrument may be routed to several parallel channels, one for each effect added to the track. This reduces effect convolution while allowing precise control over effects.
The first thing I will demonstrate is a technique for boosting a section of a track that you want to pop out through your mix. Begin by creating your source mix channel, then create a parallel channel for the same source mix channel. I generally try to keep my source mix channel at 0dB (unit gain) or as close to it as possible. The source mix channel will remain untouched except for the fact that I'm going to turn the width knob all the way left to the off position. Turned fully off the source mix channel output will be in mono. The reason for doing this will be explained later when I explain parallel reverb.
Now for our parallel channel, I often label this "Boost" as shown in the below screenshot.
Next I will turn on the SSL's high pass (HPF) and low pass (LPF) filters in the "Boost" parallel channel. So, where you would normally apply EQ to boost frequencies in your mix, you're going to "draw" your filter curve for that frequency region instead. Below you will notice I'm applying a narrow scoop and I've also drawn a HF Gain/Frequency Bell to cut out some of the high end off the low pass curve.
Rather than applying an EQ curve in your source mix channel, you can sculpt the mix presence with the above filter curve in the "Boost" parallel channel. The "Boost" parallel channel is increasing the average volume, but only for this region of the frequency spectrum from the source mix channel. You can sculpt your sound with this curve by moving it left or right, and you may also make it more wide or narrow to taste.
Second is adding an effect to the "Boost" parallel channel's narrow band. For this I'm using flange effect, as it complements this region of the spectrum that I cut out as well. To do this you should solo the "Boost" parallel channel and with the fader at 0dB (unit gain), you turn on the effect send you want to use and dial it in for subtleness. Now you should hear a texture change. You have effectively added dynamics in this tiny range with sculpt-ability and high precision of control. Lastly remove a bit of width on "Boost" parallel channel, but not too much (keeping it at approximately 25%)
Now that you've setup your "Boost" parallel channel, you can unmute your source mix channel and dial in your "Boost" parallel channel for subtleness. At this point you should experiment by moving the curve. Use EQ to shape it a bit and get a feel for how it changes the sound, carefully listening to how your boost range sounds and feels.
The effects you can use on the curve depend on where your curve is and your sound source. I usually apply a phaser, flanger, distortion, chorus or Reason's Pulveriser (set on base pressure). Chorus works great in the high spectrum, whereas the Pulveriser works well in the low spectrum. Phasers and flangers are good for low to mid range and distortion on mid to high range, but also works in base. This all depends on how you want to texture your boost. If it does nothing turn it off. If you hear a change then dial in for subtleness, or to compliment the instrument. I find this technique also fattens up thin synth patches.
Another added benefit to this process is now you can have mix overlap and the different textures will add distinction. You still don't want to have a lot of overlap between instruments, but now you can push the boundary a bit further. Lastly, the texturing dynamic will separate the instruments more effectively.