I am not a classical musician but I have learned a bit of counterpoint and from what I remember, dissonance is usually used sparingly like on upbeats and between two passing tones. Nowadays however, I often find examples in popular music where dissonance seems more exaggerated and I am trying to understand how I can use it to good effect in my own compositions without going too far. Here is an example I really like and I think the use of the 9th note is very interesting. There is even a 9th on the downbeat of the second beat. Is dissonance used like this in classical music or is this kind of thing only familiar in pop music? Are there any rules when using such dissonance in modern popular music? For example, I notice that when the 9th appears it never falls on the same beat as the bass note and I wonder if this was intentional. Also, Would a 9th work more in the upper voices? I am a bass or low baritone, would I have to be more careful about this type of interval if my own composition was in the lower octaves. EG
I think it's a matter not of quantity but that the treatment of dissonance follows the conventions of the music's style.
You could have something in a "classical" style with dissonant diminished seventh chords held for a long time before being resolved. In terms of proportion it could be 7 beats of accented diminished seventh chord then just 1 beat of the resolving chord. That's a lot of dissonance, but because it gets resolved it's totally fitting within the style.
When it comes to pop music you need to use a different standard of dissonance. This came up in one of your other questions: How to use counterpoint to write melodies over chords. I think you really need to get away from using a definition of dissonance from the 18th century when the music is not in that style. Even by the late 19th century you can find music where the treatment of the ninth is very free and it doesn't make sense to regard it strictly as a dissonance.
I think you should read this: Temperley, The Melodic-Harmonic 'Divorce' in Rock. I think it makes clear how pop/rock music has a different approach to dissonance than "classical" music. There is some over lap between the styles, but rock does some things that classical doesn't. Pop/rock style and the sense of what is harmonious or dissonant really needs to be understood on its own terms.
A dissonance ("tension") can exist anywhere, the point is that the harmonic rhythm should be coherent with the role of the chords.
But the point is that the concept of "dissonance" is not absolute, and completely depends on the period in which music has been written (and is listened): consider that a certain point in ancient music even thirds were considered dissonances.
Since the spread of tonal music in Western culture, composition evolved as composers were constantly trying to find new directions for their expression, sometimes including aspects of other cultures that used aspects of harmony that were less "rigorous" than common practice, introducing more dissonances that gradually became more "natural".
The ninth in the example is not to be intended in the "classical" sense, which normally is a lowered ninth on a dominant chord (so, very dissonant), and is only used on the melody.
Also, the fact that it's not on the downbeat or doesn't follow the bass is ininfluent, as the melody doesn't need to use only the notes of a chord, nor follow strict rules of harmonic rhythm: in classical music, it could have been considered an appoggiatura (or anticipo, in this case), but in more modern music it's considered a more than valid note to "stop on" anyway. In this specific case it's also on the dominant (but not lowered), so it really doesn't create a problem at all.
If you're worried about the register, don't: as soon as a voice is considered "melody", it theoretically can do anything you want, even if it introduces a dissonance; the register doesn't matter that much: consider classical opera, it's not like arias for bass singers didn't use dissonances just because they sung lower notes.