All 12 notes can be valid choices to use while improvising. What makes it good or bad depends on how it is used. We will cover ways you can add chromaticism into your playing without it feeling like you are hitting wrong notes. These are neighboring tones, approach tones, enclosures, and use of diminished arpeggios.
The simplest form of adding non-diatonic notes into your improvised melodies are neighbor tones. This concept is extremely easy to grasp and put into your playing almost immediately. A neighboring tone is a note a half step below or above any note in the scale you are using. This creates a nice smooth sound that creates so many new possibilities.
Once you understand the concept of neighboring tones you can jump into approach tones. The typical approach tone is 3 notes. This is very bebopish, and cool sounding. When used in rock it sounds really hip. Guthrie Govan is known for using this kind of stuff a lot. You can think of an approach tone as approaching a note in the scale you are using from 3 chromatic notes above or below. In most places in the scale, what you are doing is simply connecting 2 different notes in the scale with a neighboring tone. You can extend this to longer approach tones by thinking about connecting the scale with neighboring tones. Django Reinhardt often used extended approach tones in a very fast chromatic scale way.
Take 2 notes above and 2 notes below your note of choice in the scale you are using. There are good amount of combinations you can come up with. A common enclosure is one above and 2 below. This is a very popular type of chromaticism in bebop and sounds extremely cool. You have seen each of these so far have added on to previous knowledge, starting with neighboring tones. Now we will take a little bit different approach to adding chromaticism to your solos.
To fully understand this concept I am going to explain some theory behind it.
1) A Diminished chord is often a substitute for a dominant chord. When chords have the same function, they often substitute for each other. There are only 4 diminished chords, after that they repeat in an inversion.
2) Often diminished chords are used as passing chords. For example you could play the chord progression C – Dmin like C | Db Dim | D-. This works because the diminished is working as a secondary leading tone. This also means you can add a secondary dominant. The secondary dominant would be C | A7 | Dmin. Most chords are capable of having secondary dominants and leading tones.
3) Implying chords simply means playing around other chords that are not written. Or in other words you are using notes that are note emphasized by the rhythm section.
So how does this work? You imply a bunch of chords. Let’s say you are playing in the key of G. You can play a G arpeggio, G# Diminished arpeggio, A minor arpeggio, A# diminished arpeggio, B minor arpeggio, C arpeggio, etc. This allows for tension and release as well as creating a chromatic root line.
All of these approaches to adding chromaticism are not meant to withhold your creativity, they can be play with your stylistic manners. You can articulate them differently, put different rhythms to them, Different notes, Mix them up however you wish. These are just a few proven ways to use chromaticism to spice up your solos.