The document discusses the concept of timbre, which refers to the characteristic quality of a sound that allows the human ear to distinguish between different musical instruments playing the same note. Timbre is determined by the complex frequency spectrum of each note, including the relative volumes of different harmonics. Understanding timbre is important in music production, as the goal is to accurately record, store, and reproduce the characteristic timbre of different sounds and instruments. Sonograms provide a visualization of a sound's changing frequency spectrum over time, revealing the differences in timbre between instruments like violins and trumpets.

1. Hello, let me introduce myself, I am Fabien Viale from Nice, France. This
lesson is for week 1 of Introduction To Music Production at Coursera.org. I
will be teaching some knowledge on audio basis, especially focused on the
notion of timbre. Please excuse me in advance for grammar or vocabulary
mistakes, as English is not my first language.
1) What color is Sound?
This question was asked to Radio Luxembourg listeners concerning Pink Floyd
first radio hit "Arnold Layne". Listeners where asked to guess which hue
the song suggested.
Musicians may have already an idea of what would be the "color" of a song.
Musically speaking, we know that different scales (major, minor) produce
different moods from bright, happy, to dark, melancholic.
But as there is a color to music, there is also a color to individual
sounds inside the music. "timbre" is the answer to this question : "What
color is sound?"
A piano, an electric guitar with a clean sound, an e-guitar with
distortion, all playing the same note (pitch) will definitely not sound the
same. All of them will have a different audio imprint that we call timbre.
It is important to notice that the notion of timbre is closely related to
human audio perception. It is "how" the human perceive the difference
between a flute and a clarinet playing the same note. It is thus a term of
psychoacoustics. The real physical characteristics of sound that determine
the perception of timbre include spectrum and envelope. The spectrum is the
decomposition of a sound in terms of frequencies, and the envelope is how
the volume of the sound varies in time. The timbre of a sound is
traditionally visualized with a Sonogram, which displays the evolution of
the spectrum (energy per frequency) over time.
2) What causes timbre?
The perception of different timbre between different musical instruments is
due to the fact that each note from a musical instrument is a complex wave
containing more than one frequency. If there was only one frequency
involved when playing a note, the notion of timbre could not exist and a
piano playing an A at 440Hz would sound exactly like a trumpet playing the
same note, and would sound like a sinus wave.
It is the characteristics of a sound with relation to its frequencies which
makes the timbre. And by characteristics we mean as well “character”. The
character of a timbre for example would be that it has plenty of energy on
some specific frequencies, and very little on others. For example a drum
kick will have plenty of energy on the low end spectrum, where a charley
would be much more concentrated on the high end.
It could be as well that its attack is brutal (like a snare drum) or smooth
(like a violin).
Timbre is not only related to musical instruments, it can describe any
sound. The human voice has a timbre, and that's why we are able to
recognize the voice of one person or another. A singing bird has a timbre,
as well as a train passing by.

2. 3) There is timbre and timbre.
There is one specific property of the sound that has fascinated humans for
millenniums.
We know that the sound is a vibration of the air. In most cases, this
vibration is chaotic. But in some cases, this vibration is well ordered and
follows the mathematical property of a periodical movement. And this
periodical movement of air is pleasant to human ears, probably because it
is rare, different than the common chaotic movements.
It is the same thing which happens when a stone is thrown in the middle of
a calm lake. Circular periodic waves appear progressively starting from the
stone impact. And people would stop and watch it, as being something
pleasant to contemplate. If the wind comes, those periodic waves would be
replaced by scattered, chaotic waves, which is not as pleasant to our eyes
(well that’s a matter of taste).
In term of sound, this analogy refers respectively to music and noise.
Music is the harmonic periodical movement and noise is the chaotic
movement.
So we would imagine, ok cool, so now we know what’s beautiful and what’s
not, let’s do some cool stuff with pure sinusoidal waves! Even if you
haven’t tried yet to create something beautiful with only sinusoidal waves,
I’m sure you get the picture to how boring it would sound like!
And there comes the complexity of human nature, we need order, but not too
much, we need as well excitement, movement. In music, all this excitement
comes from:
- The volume of each harmonic (integer multiplier) of the fundamental
pitch of the sound. Some musical sounds have all there harmonics (1x,
2x, 3x, 4x, etc), other sounds have only even harmonics (1x, 2x, 4x,
6x, etc). there are as many possible combinations as we could think.
- The presence of noise-like artifacts (transients). For example, we
can sometimes appreciate to hear the hammering noise on a piano, the
blowing attack on a flute, etc.
- The evolution of all this in time
In the sonograms below, we see how the timbre of a violin compares to the timbre of a trumpet.
Where the violint has a long range of harmonics slowly decaying from the fundamental all the way to
15 kHz, the trumpet has its first three harmonics with a lot of energy, but decays rapidly afterwards
and don’t produce harmonics above 9kHz.
1 - Trumpet
2 - Violin

3. Finally in the figure below, we see two other examples of timbre. The left one is the noise produced
by creasing a scrap of paper. You can see it there is not much white in it. It means it has nearly all
frequencies possible. We call that a “white” noise and it’s very often use in order to test the
spectrum response of an audio equipment or a room. The right one shows vowels sang by a human.
4 - Paper noise
3 - Vowels
In conclusion, the timbre is the imprint of sounds, it defines their color, their character, how they
evolve in time. Understanding the principals behind the concept of timbre is essential in music
production. The purpose of the audio chain is exactly that, how could we record, store, and diffuse
the timbre of an existing sound ? How can we shape it to our need ?