Transcript image by Hans-Christoph Steiner based on Grey, JM 1979, JASA

On Timbre
Phy103 Physics
of Music
Four complex tones in which all
partials have been removed by
filtering (Butler Example 2.5)
One is a French horn, one is a violin, one is a pure sine,
one is a piano (but out of order)
It’s hard – but not impossible to identify the instruments.
Clues remain (attack, vibrato, decay) and these
contribute to the “timbre”. Timbre is not just due to the
spectral mix.
Attributes
from Erickson’s Music Structure
Subjective
Objective
Tonal character, usually
pitched
Periodic sound or sound
composed of only a few
frequencies
Noisy, with or without some Random pulses or broad
tonal character, including
band spectrum
rustle noise
Vibrato
Frequency modulation
Tremolo
Amplitude modulation
More Attributes
Coloration
Spectral envelope
Coloration glide or
formant glide
Change of spectral
envelope
Attack
Prefix
Final sound
Suffix
Beginning/ending
Rise/decay time
Schouten’s “Acoustic
parameters”
1.
2.
3.
4.
The range between tonal and noiselike character.
The spectral envelope.
The time envelope in terms of rise, duration, and decay.
The changes both of spectral envelope (formant-glide)
and fundamental frequency (micro-intonation).
5. The prefix, an onset of a sound quite dissimilar to the
ensuing lasting vibration.
This represents way too many free parameters for an engineer
to cover the complexity of sounds.
Timbre
space
•
•
Grey’s Timbre cube
Is it possible to classify
timbres, for example
recognition of instrument
from audio?
image by Hans-Christoph Steiner based on Grey, JM 1979, JASA, 61, 1270
Timbre space
based on
nearness ratings
by people
Psychology
experiment
From McAdams, S. et al. Psychological Research, 58, 177-192 (1995)
Broad band vs Tonal
“Beat That” by Beat Kaufmann
Hz
The
Syrinx
Filtered Broad Band
• ASA demo 5
• A Low pass filter cuts off all high
frequencies
Blending of harmonics into one
tone or timbre
ASA Demo 1 Cancelled Harmonics
20 harmonics of 200Hz are played
together.
When the relative amplitudes of all 20
harmonics remain steady they blend and
we hear them all as one tone
When one harmonic is cancelled or given
a vibrato then it stands out and we hear it
separately
How many harmonics are needed for a
tone to have its recognizable character?
• ASA Demo 28 Adding in
partials of a carillon bell
Hum note 251 Hz
Prime or fundamental 501Hz
Minor Third and Fifth 603,750Hz
Duodecime or Twelfth 1506Hz
Upper Octave 2083Hz
Next two partials 2421,2721Hz
Remainder of partials
Adding in partials for a guitar
ASA Demo28 In order
•
•
•
•
•
•
•
•
fundamental
2rd harmonic
3rd harmonic
4th harmonic
5th and 6th harmonic
7th and 8th harmonic
9th, 10th and 11th harmonic
Remainder
What are the characteristics of
sounds used for music?
Properties of musical sounds
• Composed of tones, not alot of broad band
noise
• Overtones are nearly harmonic
• Lots of exceptions to the above rules
Timber and Transposition
• High and low tones from a musical instrument do
not have the same relative spectrum.
• Low notes on the piano have week fundamentals
whereas high notes have strong ones
• ASA Demo30 shifting the spectrum of a bassoon
down
The effect of Tone Envelope
on Timbre
ASA demo29
Piano envelope is normally decaying
but here it is reversed
Tones and Tuning Stretched
The scale can be stretched
The partials can be stretched
Here are examples of all 4 combinations
-- pure harmonics and normal scale
-- scale stretched
-- partials stretched
-- stretched harmonics and scale 1 octave=2.1
Changes in Timbre
The singer’s formant
• Cook demo 42 Singing with and without
the singer’s formant
spectrum with singer’s format
spectrum without
Changes in timbre with vocal
effort
Cook demo #78
a)
b)
c)
d)
Successive vocal tones, amplitude only turned down
Same as a) but high end of spectrum is also turned
down, as would happen for decreasing effort
Same as b) but with additional reverb that is held
constant so voice sounds like it is getting quieter in a
fixed location
Same as a) but with increasing reverb so the voice
sounds as if it is getting further away
Terms Introduced
• Timbre space and popular choices for their
dimensions