This is a technique to control the vocal placement in the mix. Make it stand out or blend. The principle is to group instruments separately and vocals separately to make room for or reduce vocal characteristics with EQs.

Start by routing each and everyone of the instruments to a bus (BUS1). Now, by lovering the bus volume you should only hear the vocals.

If yo have more then one vocal track you should group them to another bus (BUS2).

   BUS1             BUS2
    |                |
Instruments        vocals

The example in this blog post has only one vocal track, so there’s no actual benefit of routing it to a bus.

INSTUMENTBUS
      |                  |
 Instruments         Lead Vocals

On vocal track ( or vocal bus if created):
Use a parametric equalizer and sweep over the frequency-band to find the vocal characteristics. When found, gain a few dB. Then isolate it by narrowing the bandwidth.

On instrument bus:
Since the instrument bus contains several instruments, it’s difficult to identify a joint characteristic. Therefore a simple approach is to use a parametric equalizer with the same center frequency as for the vocal track. Reduce gain a few dB. Then isolate it by narrowing the bandwidth.

What you have managed now are the vocals to stand out. Now lets compare the original and the EQed song.

 Original song

 EQed song

If you instead want the vocals to step back or blend. Invert the gain of the vocals and instruments.