Tuesday, 8 March 2011

#2: Attack of the Guitar Pick!

Let's say you record the same guitar part two times. The first time you play the part very softly, gently plucking the strings with every note and chord. The second time you play as hard as you can, hitting all the notes accurately, but with all of your might. Our intuition says that both recordings would sound different, even if the volumes were matched. Louder sounds louder even if isn't... OK, but how? That's what we're going to look at today: how does "playing harder" affect guitar tone?

We'll pluck the same string over and over again; sometimes we'll pick harder, other times softer. Then we'll look for differences in the sound. First, we'll look at our classic sound characteristics—brightness and sustain—for the full duration of each pluck (see first blog). Then, we'll separate each pluck into two parts: the attack and the decay. For each part, we'll determine the brightness and sustain separately.

As usual, the guitar is a Fender Telecaster (American Standard) with D'Addario regular light strings (0.010–0.046). The 3rd string (G) was used for this experiment.

> The whole signal. Brightness goes down (a little) with harder picking, and sustain drops significantly. There may be a relationship between these two trends: higher harmonics ring longer than lower harmonics ("On the sensations of tone," Part I, Chapter IV, H. Helmholtz), and if louder sounds aren't as bright, as we see here, then it would make sense that they don't ring for as long. (It may be a good time to note that these sustain values are based on a drop of -20 dB from the signal maximum. If we were just looking for the point where the signal got silent, then louder sounds would certainly ring for longer, as our intuition would suggest.)

> Attack! The brightness trend here is similar to that for the entire signal: a slight decrease in brightness for louder sounds. Because the attack region is so short (one second), an alternate method for expressing sustain was used: the volume drop across the region. There may be greater sustain (i.e., less volume drop) over the attack region for louder sounds—opposite to the effect for the entire signal—but the data in the plot below are too messy to say for sure.

> Decay... The results here are similar to those for the whole signal: louder sounds are less bright and drop faster in volume.

Playing harder or softer leads to differences in sound beyond just a change in volume. A softer sound has greater sustain and is a little brighter, whereas a harder sound has a stronger fundamental frequency and decreases in volume more quickly.

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