Overview
As metal fans we all know the bass is typically an instrument that is usually hidden in the back of mixes. However I’d say that this is quite different with Tool. Keep in mind that not every single band needs to have the bass on the forefront because that sometimes just isn’t the style needed. For more traditional metal the bass is more there to back up the rhythm guitar sections. In Tool every instrument has their own space to work with.
Most Tool songs have a bass motif that occurs throughout most of their songs. The obvious one here is Schism because almost everybody knows the opening bass line. The actual bass line is important to grasp the listener, but the tone of the instrument is also as important when it comes to the enjoyment of the listener.
I believe that his bass tone hits all the aspects of what I think makes up a good tone for any instrument. His dynamics are almost unmatched when comparing him to other bassists. My preference for bass tone is a thick low end and a punchy high end. In my own experience of trying to make my bass tone to my liking I always found it hard to do. If I wanted the low end to be thick the high end would lack and vice versa. Then again I wasn’t using the same equipment that he was using but it shows that he was looking for that tone. The beginning to The Grudge is another great example of the punchy high end.
Gear
Of course, everything in music is objective so you might not agree with my opinion here and that is totally ok. If you want to take a look at what Justin uses live you can check out the link below.
https://equipboard.com/pros/justin-chancellor?gear=amplifiers