Touch, Dynamics, and Accents
All over the internet, whenever someone asks how to sound like some famous artist, you'll read, "Tone is in the fingers." It's true. There's more to playing than putting your fingers on the right frets and plucking the right strings. We already covered how to cleanly fret and play notes in Basic Technique. Other technique lessons on legato, bending, and vibrato will help add flair to notes. We also alluded to good right hand technique and the various methods to alter tone and dynamics in picking. Here we will expound upon picking hand technique.
This is mainly designed for single note or small chord playing - generally riffing or lead. This is less important for strumming chords, which is more focused on rhythm.
Contents
Pre-Reqs
Recap on Picking Technique
Let's start with a recap on picking. The pick should be pointing directly towards the face of the guitar. Your picking motion should be parallel to the face of the guitar, moving "through" each string. No "pecking" or "popping", and no picking diagonally through the string, which can lead to sliding the pick on the string, causing a scratchy or noisy sound (see Basic Technique).
For speed, It should be held perpendicular to the face, allowing you to easily alternate between downstrokes and upstrokes without losing speed. Your picking motion should come from the wrist or elbow, not the thumb or finger joints. This will help keep a consistent rhythm both on a single string and when picking across strings (see alternate picking).
A Fresh Look at the Mechanics of Picking
I like to break down the mechanics of the pick's interaction with the string as 3 different periods, separated by 2 key events. The periods are approach, displacement, and resonance. The events between them are contact, and release. Chronologically, that's approach -> contact -> displacement -> release -> resonance.
Approach
There's nothing too special here. You've decided to pluck the string and started your picking motion. The most important thing is the position of your right hand, how you are holding the pick, and how you are carrying out the motion (finger/thumb, wrist, and/or elbow joints). This will determine the velocity, location, and angle of the pick when it contacts the string. While these things can and sometimes require alteration in the middle of a picking stroke, most of the time it is too late to change anything once you've made contact. Any change that occurs is due to the string's resistance to being displaced or just the subtle changes in angle that are a result of the pick being moved by a close or distant fulcrum (finger joints vs. wrist vs. elbow).
The approach is not necessary. You may being your picking stroke with the pick already pressed against the string. I often do this to mute the string, then get a near perfectly "clean" sound to the note.
Contact
Contact is when the pick first touches the string. If the approach was lengthy with a high velocity, there will be a slight audible thud on contact. It will be noisy rather than musical. This can be desirable or undesirable depending on context - it adds more noise and volume to the initial attack portion of the note, making it sound more raucous. On the other hand if the approach was basically non-existent, there will be no thud, and the note will sound cleaner.
Displacement
Displacement is the pick pushing the string away from its natural resting position. The sting naturally resists displacement, with more and more force required to displace it further and further. The pick's material and thickness will determine how far the pick is able to do so. Also in play is your grip strength on the pick - the string puts torque against the pick relative to where you are gripping it. Ultimately, either the pick or your fingers will give in allowing the pick to become angled in relation to the guitar's face, so that the string begins to slide down its edge and off the tip. This is called the release. (Of course the string will break before becoming severely displaced, if using some incredibly extreme picking method.)
Other factors that determine how much displacement is available are the shape of the pick, and the angles it is held incident to the guitar's face and the string. In relation to the guitar's face, it can "hook" the string, avoiding release. Or it can allow for less displacement. Similarly, angling the pick in either direction away from perpendicular to the string offers less and less ability to displace it, varying depending according to the pick shape.
Release
While the release is nothing too interesting - just the string finally freeing itself of the force of the pick and attempting to return to its at-rest state, the transition from displacement to release is more interesting. Depending on the amount of displacement as well as the angles, shape, and material of the pick, as the string slides down the edge (or face) of the pick, it will make noise. Most of the time this will sound scratchy, although some smoother materials may be quieter than others. This energy does transfer into the string, which will resonate on each side of the pick. Thus, pick location on the string matters to this sound, and it is why pick slides have their characteristic sound.
Resonance
As the string attempts to return to rest, its elastic properties cause it to overshoot the at-rest location, bouncing back and forth and producing the desired frequency (and its overtones). This is resonance. Usually, all the previous parts of the picking mechanism can be thought of as noisy, while this is considered musical. However, depending on the amount of displacement, the thickness of the strings, and the guitar's setup, when the string attempts to resonate, it may slap against frets or otherwise create noise.
Also, the location where the string was picked also determines how the string will resonate - the balance of its fundamental frequency vs. its overtones, as well as its amplitude over time - its characteristic attack vs. sustain vs. decay signature.
Pick Angle Incident to the String
Trying to pick the string with its face completely parallel to the string can cause the entire face of the pick to rub against the string during the picking motion. Depending on the type of pick, this may cause hang-ups or other undesirable obstructions to a smooth picking motion. So you almost always want to have the pick angled at least somewhat off of parallel.
The degree to which you do so will affect how easily and how quickly the string will slide down the pick's edge. It also affects how easily the pick or your fingers can flex as the string pushes back more and more against the pick. This affects how far you can displace the string thus your level of dynamic control. It also changes the relative volume of the string sliding against the string vs. its resonance after release.
Usually you want to be just slightly off from parallel to the string. This allows you the maximum dynamic control, with the pick or your fingers' flex naturally allowing it to release as you hit the critical point of displacement. It also has the most resistance to the string sliding down the pick edge, allowing you to displace the string further than you otherwise would.
That said, you may not always want that. Different angles can give different pick attack noise signatures as well as affect the level of overtones vs. the fundamental frequency. A lot of this depends on the pick material and shape, and the exact nature of your picking motion. Its best to experiment with it. A completely perpendicular angle is going to be sharper on the string than otherwise, and with an approach that has significant velocity, this can also trigger harmonics in the string.
Location on the String
Exactly where on the string you pick the string has a huge impact on the resulting tone. Picking closer to the center of the resonant portion of the string (halfway between the fret being held and the bridge) will give a strong balance of fundamental and overtones, resulting a square wave type tone from the resonant string. (That's like an "oooooooo"). In contrast, picking closer to the bridge will give a more nasal, bright tone, similar to a sitar.
The natural location for you to pick is between the pickups or over the neck pickup. This means for riffs or chords where the fretted notes are lower on the fretboard (towards the nut), the tone will be the bright, somewhat nasal tone we are familiar with. As you move towards 12th to 15th position, your picking location will naturally be at the center of the resonant strings, getting that singing lead tone.
But don't rely on changing positions to dial in that tone. Move your right hand around to try some new tones out. For an extra smooth lead, make sure you are picking exactly in the center of the resonant portion of the string; move back towards the bridge for a more aggressive tone.
Dynamics and Fret Buzz
As you pick harder and harder, the resonance of the string will naturally get louder and louder. From inaudibly low strength to medium-high strength, things go as planned. There are differences to how loud the initial attack vs. the more lengthy sustain is, with the attack being relatively louder the stronger you pick.
However, at a certain point, a heavy stroke has the attack resonate so wide that the string will start slapping against the frets. This naturally makes a brief metallic popping or clanking, adding an extra emphasis to the energy of your playing. It can really help to accent key notes, or to demonstrate the energy in a few measures of power chords.
Picking even stronger, you can get even the sustain portion of the resonance to slap against the frets, getting a consistent buzz. This will overpower the actual note itself, and should be used sparingly.
Breaking down the Rules
When you're looking to really highlight a note, it's often preferable to break some of the guidelines previously established. Using the thumb and finger joints to pick can sometimes attain a higher degree of dynamic control. It can also allow easier or quicker angling of the pick as described above.
Rather than picking directly through the string, you may want to pick diagonally through the string, to add some scratching to the pick attack.
Pick Angle Incident to the Guitar Face
Above I described rotating the pick, so that it attacks the string at different angles, causing it to have more or less resistance to the pick, thus determining the level of dynamics achievable and subtly altering the tone of the pick attack. But we still wanting to have the tip of the pick pointing directly at the face of the guitar.
When the pick is angled non-perpendicular with respect to the face of the guitar, one of two things happens. Either it will "hook" the string, causing the string to become stuck between the tip of the pick and your fingers as you try to displace it. Normally, this is bad because it makes picking more difficult and can throw off your rhythm. The eventual release may be overwhelmingly strong, causing from fret buzz, as described above. Or there may be no release at all causing you to miss the note altogether. Now, these are certainly concerns for a novice, which is why I recommend a strict perpendicular hold while gaining confidence with the pick. As you develop control, you can actually use this to your advantage. A slight hooking of the string is the only way to gain absurdly strong dynamics to notes. So long as you are aware of the complete mechanics of the picking motion, you can apply a hook to displace the string heavily, before relaxing your pick angle slightly to allow the string to release from the pick and slam into the frets and create a huge accent.
On the other hand, angling the pick the other way will make it difficult to impossible to apply tension to the string without pushing through it and getting an early, weak release. The sound of the pick sliding against the string may be as loud or louder than the sound of the ensuing resonant string. Again, this is bad practice for a novice trying to gain pick control, but another weapon in the arsenal of a master. It is like the reverse of an accent. Your audience can hear that you are trying to playing a note, but barely anything musical is voiced. It is like a dying man trying to utter his last words - the incident noise is there, but what is he trying to say? In the extreme it is painful to listen to (just like a ridiculously strong accent). But done tastefully, it can earn you legendary status.
Accents
Accents are a technique where certain notes are given more emphasis than others generally by means of having louder dynamics. (Another technique include turning on/off an effect for that one note.)
Notation
Accents are commonly notated with a > symbol above the note in tablature:
Accents on the downbeat: 1 2 3 4 1 2 3 4 > > --0--0--0--0-|5----------
When accents two levels of accents are required, '>' is used for normal accents, and '^' is used for stronger accents:
Accents on the downbeat, strong accents on backbeat: 1 2 3 4 1 2 3 4 > ^ > ^ --0--0--0--0-|5--5--5--5--