Timbre
What is the difference between a tuba and a
flute (or, more accurately, the sounds of each)?
How do we tell the difference between two people
singing the same song, even if they¡¯re
singing exactly the same notes? Why do some
guitars "sound" better than others
do (besides the fact that they're older and
cost more and have Eric Clapton's autograph
on them)? What is it that makes things "sound"
like themselves?
It is not necessarily the pitch of the sound
(how high or low it is) ? if everyone in your
family sang the same note, you could almost
surely tell who was who, even with your eyes
closed (it's not by smell, or even just the
fact that grandma sings out of tune). It¡¯s
also not just the loudness ? your voice is still
your voice whether you talk softly or scream
at the top of your lungs. So what¡¯s
left? The answer is found in a somewhat mysterious
and elusive thing we call, for lack of a better
word timbre, and that's what this chapter is
all about.
Actually, we have to admit that timbre (pronounced
"tam-ber", and not "tim-ber"
as in "look out below"!) is a kind
of sloppy word, inherited from previous eras,
that lumps together lots and lots of things
that we don't fully understand. One of us thinks
we should abandon that word and concept entirely,
and compares it to the nineteenth century concept
of the ether, through which lightwaves were
supposed to travel. But it's one of those words
that gets used a lot, even if it doesn't make
much sense, so we'll use it here too? we're
sort of stuck with it for the time being. Maybe
the best definition for it is everything that's
not pitch and amplitude (but even that doesn't
work, because pitch and amplitude are part of
timbre too... okay, we'll stop now).
What
Makes Up Timbre?
As we mentioned, timbre can be roughly defined
as all those qualities of a sound that aren't
just frequency or amplitude. These qualities
might include:
Spectra: the aggregate of simpler waveforms
(usually sine waves) that make up what we
recognize as a particular sound. This is what
Fourier analysis gives us.
Envelope: the attack, sustain, and decay portions
of a sound (often referred to as transients).
Envelope and spectra are very large concepts,
and include a lot of sub-categories. For example,
spectral features are very important, different
ways that the spectral aggregates are organized
statistically, in terms of shape and form.
For example the relative "noisiness"
of a sound is a result, in large part, of
its spectral relationships Many facets of
envelope (onset time, harmonic decay, spectral
evolution, steady-state modulations) are not
simply explained by just looking at the envelope
of a sound. Researchers spend a great deal
of time on very specific aspects of these
ideas, and it's an exciting and interesting
area for computer musicians to research.
It's helpful here to bring another descriptive
term into our vocabulary: spectrum. Spectrum
is defined by a waveform's distribution of
energy at certain frequencies. The combination
of spectra (plural of spectrum) and envelope
help us to define the "color" of
a sound. Timbre is difficult to talk about,
because it's hard to measure something subjective
like the "quality" of a sound. This
concept gives music theorists, computer musicians,
and psychoacousticians a lot of trouble. However,
computers have helped us make great progress
in the exploration and understanding of the
various components of what's been called,
traditionally, timbre.
