Why does a violin sound different from a horn?

Several kinds of audible information

Pitch

Timbre

Attack

Decay

Vibrato

Thus, we need to quantify sound

Thus, we need to measure sound

We need to systematically compare sounds…

The Waveform• Plot motion of air (pressure vs. time)

time (ms)

pres

sure

• Microphone converts pressure to voltage

Compare Waveforms

period

T = 2.2 ms

T = 7 ms f = 1/T = 140 Hz

f = 1/T = 460 Hz

pure tone sine wave

• Single period implies a single, constant frequency• Described by only two numbers: f, A

ampl

itud

e

period

How can we describe more complicated sounds?

simplest sound simplest waveform