Here is an answer to you question and give you a different perspective on the problem.
Let's look at a jam with Am - G - F - F
for now, in std tuning (EADGBE). Playing the roots on the 6th string, you'll play using the CAGED chordal system. That's great. Track one guitar doing that, and track a second guitar playing inversions.
Am = A C E: Root, minor third, fifth
G = G B D: Root, third, fifth
F = F A C: Root, third, fifth
The minor third and major thirds in these three chords give the tonal movement you're after. Typically, these notes will be buried inside the 'standard' chord shapes on the guitar, but if you play inversions and let them be the highest notes of the chords, you'll really accentuate the movement in the melody.
Harmonic Minor & Chromatic notes
One of my favourite techniques.
In the key of C, the 5th degree is G Major chord. G Major has a B in it, which is one semi-tone away from C and thus provides a bit of suspense/ tension. Playing a G Major followed by a C Major gives a feeling of resolution. In the minor key, you don't get that resolution by moving from the Em to Am for instance. The way to get that tension, is to play E Major in place of the E minor.
(Resume) So, now that you're playing some nice CAGED chords, and some inversions (playing them up near the 12th fret for a 'pretty' sound), you can cycle through Am - G - F and occasionally drop down to E Major.
Am - G - F - F
Am - G - F - F
Am - G - F - F
Am - G - F - E
What makes this sound interesting is the notes played in order, C - B - A - Ab. It's got a nice chromatic movement going on which will really catch the ear, you won't find that movement inside the diatonic scale. When you resolve from the E Major, to Am, it is quite powerful.
Pink Floyd's Comfortably Numb starts out with a few bars of B minor chord, layered with a B- power chord. It then proceeds to play B min - A Maj - G Maj - E min chords. After a chorus, B min is replaced by B sus 2. Later in the song, I think it returns to B min.
- major = Happy
- sus4 = even more joyful
- minor = sad
- sus 2 = depressing,
Pink Floyd's twenty something minute song Echoes, from the B-side of Meddle, has a very interesting approach with chords. In the verse it uses C# min, G# min, F# min, G#7.
In the chorus it changes to really interesting C#, G#, F#m, G#7 (you won't see a movement like this using the diatonic system). Then there is the famous bit C#, C, B, A#, A.....A, A#, B, C, C#..... which, so I understand, Pink Floyd took Andrew Lloyd Webster to court over for copywrite infringement (Phantom of the Opera).
Echos takes the listener on a journey, invoking a number of mixed emotions along the way.
Hawkwind's 2010 album Blood Of the Earth features a song called Sentinel. It follows the progression, Em, C, Bm, C. The chorus then plays G, D#, Dm, D# - not in the same diatonic scale as the verse. When I heard it for the first time, I was very impressed, and I still am.
Arpeggios & Delicacy
Strumming can be good fun, it can be used to convey gentle or aggressive sentiments. Playing single note lines from chords (listen to the Hawkwind example), can convey a delicate sound. For sad music, delicate sounds can be useful. The Hawkwind example plays two ascending notes from the 'bottom' of the chord, then the descending notes from the 'top' of a chord.
Let there be silence
I heard a quote from Roger Walters a number of years ago. To paraphrase, "Don't play stuff for the sake of it. Sometimes, it's better to let there be gaps between parts, room for the music to breath.
According to Spinal Tap
Dm is the saddest key.
Sometimes, a lack of major or minor tonality can be just as useful by employing 5th chords. You'll see this technique used in a number of Pink Floyd songs, notably songs from The Wall album.
Dynamics & The Sound War
Industry production of music entered the business into The Sound War, an arms race of volume. Loudness tends to be a big factor in the success of a song. People tend to like louder volume music. Queen famously had their engineer remove the limiter from a Live Aid gig during their set and replace it with their own. According to the story, they were MUCH louder than everyone else, and their performance has gone down in history as one of the best. Loudness and record sales have shown positive correlation. Mix engineers try to maximise the volume of music played over the radio by using compression and limiting. When you listen to a song next, watch the volume meter jump up and down. If its a song from the last 20 years, you'll probably see it jumping around the yellow and red section of the meter. Nowadays, the sound war is starting to fade with most music being streamed online rather than purchased on physical media or consumed on the radio. YouTube is leading the way, by normalising the music (turning it down). This allows the engineers to make use of dynamics when mixing songs! Dynamics doesn't mean play quietly. It means play quietly when it works for the song, and play loudly as well when it works for the song. Classical music makes heavy use of dynamics. Try to incorporate dynamics into your arrangement. Judas Priest and Black Sabbath use dynamics, and they are Heavy Metal. They have some great songs. Judas Priest's Beyond the Realms of Death is a sad song. The band has two guitar players and they really can play well. Notice how the song uses an arpeggied minor chord with a descending bass note during the clean/acoustic guitar sections, then goes into raging power chords for a powerful effect during the chorus. Black Sabbath's Wheels of Confusion is an interesting song to listen to. The introduction is quite sad, then the verse kicks in and it's more upbeat. When you get about 5 minutes 10 seconds into the song, the tone changes completely and turns very dark.
Finding different places to play chords on the neck
Basic chord theory:
- Major chords are comprised of a Root, Major Third and a Fifth note.
- Minor chords are comprised of a Root, Minor Third and a Fifth note.
- Sus 2 chords are comprised of a Root, Major Second and a Fifth note.
- Sus 4 chords are comprised of a Root, Perfect Fourth and a Fifth note.
There are some very informative tutorials on the major scale, the minor scale and chord construction. I learnt from the Dorling Kindersly Complete Guitarist. It's a wide topic, but its very rewarding to learn even the basics. With this knowledge and the knowledge of which note is played at each fret of each string on your guitar (half a days learning), you will be able to pick any cluster of corresponding notes to make a chord or an inversion of a chord. There is an A minor triad shaped like part of an A Major 7th chord, which is played half way up the neck. When played in conjunction with an open A minor chord, I think it's really pleasing.
Major and Dominant Seventh Chords can be used to add flavours to your chords. For each degree, the major (capitals I, IV,V), minor (lower case ii, iii, vi) and diminished (vii) chords have next to them, listed the type of diatonic 7th chords available.
- I - Maj 7
- ii - Dom 7
- iii - Dom 7
- IV - Maj 7
- V - Dom 7
- vi - Dom 7
- vii - Dom 7b5
Sometimes they add embellishments which are great. Sometimes, they really detract from a passage. An A minor 7 chord (A C E G) has C E G in it which are the notes of a C major chord. If you have a C chord in a passage and want some variation, try replacing your C with Am7. Play it in a jam such as
Em, D, C, C
Em, D, Am7, Am7
Wikipedia has an introduction article to chord substitutions. There are some very interesting uses of substitutions which you can hear in music by The Beatles.
Summary: How to use your guitar to make a song sad
- Have a story in mind to tell, and use your instrument to tell it by applying dynamics, chromatic movements, arpeggios and other techniques.
- Variation is a big part of keeping the attention of listeners. We humans are remarkably good at blocking out repetitive things in order to dedicate more 'brain-power' to other tasks. Add variation to your song, and you'll maintain attention. Variation also provides you with the opportunity to give mixed emotions during different parts of a song. If you want an example, queue up 16th note hi-hats in a DAW and play 4 bars worth. You'll see it grates on the ear. now apply randomised velocities and some randomised positioning, (in logic pro the humanise function does this), and notice the difference.
- Use dynamics
- Don't play notes/ chords for the sake of it. Let the music breath
- As a musician, you're job is to manipulate and guide the emotions of the audience. Find chord progressions, strumming/arpeggio patterns and tempos which allow you to do so.
- Listen to other people's music which you like and re-create their songs. You'll learn and remember more technique by re-creating a handful of songs than you will by reading