I take online acoustic guitar lessons with Bryan Sutton, who is one the greatest bluegrass acoustic guitar player of all time. He says one of our important single string articulations for accenting the musical phrase is a downstroke versus an upstroke. He says the downstroke is rich and full bodied, while the upstroke is thinner sounding.
I tried this and this tonal difference is true. But it is true when I downward pick slant, but what I found is that I can reverse this tonal difference when I upward pick slant and get a fuller tone on the upstroke.
So here is what I think is going on.
With a downstroke using a downward pick slant, where the downstroke brings the pick below the strings, the downstroke actually pushes the string slightly towards the body of the guitar, and after the immediate release of a downstroke, the string has an initial acceleration vector that travels away from the body of the guitar. The strings initial energy is away from the guitar, away from the frets, away from the bridge, and away from the nut.
With an upstroke using a downward pick slant, where the upstroke brings the pick above the strings, the upstroke actually pulls the string slightly away from the body of the guitar, and after the immediate release of an upstroke, the string has an initial acceleration vector that travels toward the body of the guitar. The strings initial energy is slamming toward the guitar, into the frets, into the bridge, and into the nut.
The string travel and tone is reversed if you switch to an upward pick slant.