Remember that our topic is processing Rock Vocals, so whatever is good for Pop or R&B will likely be unsuitable here. You rarely hear a shimmery top end in Hard Rock, so if a mixing and mastering services engineer needs to make a singer’s voice brighter, the choice of 10+ kHz range will be a mistake. The appropriate selection would be around 5-8 kHz, which is a more edgy range of high frequencies declared by most mixing engineers.
Generally, paying special attention to the treble processing is only worthwhile if it was insufficient in the record initially, or if it’s intended to “cut through” the bright guitars. The general presence in rock music lies in middle frequencies, and the mixer has to find the right balance of the top end for the voice in the context of the song. Otherwise, the voice completely disappears behind the wall of the guitar sound.
This is where the focal point of this genre vocals lies. There are two most important frequency ranges for the vocals: the upper mids (1-4 kHz) and the 300Hz-1kHz zone (the lower mids). It is the upper midrange that should be the focus in aggressive rock styles (Death Metal, Hardcore), and not the top end. The upper midrange makes the voice fully audible behind the heavy guitars and should be taken to account at online audio services.
Mixing mastering vocal with the emphasis on the lower midrange is more typical for rather gloomy Heavy Rock styles. Here, the engineer might highlight this range in order to keep up the overall vibe, but the level of vocals in the mix will have to be lifted to maintain a correct balance. Interestingly, the vocal track in solo mode might seem too midrangy and etched, but if you turn on all other elements, everything will fall into place!