Slide 2 Sound Synthesis Part I: Introduction & Fundamentals
Nicolas Pugeault [email protected]
http://info.ee.surrey.ac.uk/Personal/N.Pugeault/ Slide 3
Introduction Instruments can be made in a variety of ways: think
guitar, piano, organs, etc. Use electronic devices to create
sounds: synthesisers. Can either Recreate an existing timbre or
something different. Slide 4 Introduction Producing a sound by
sending an electrical signal to a speaker is trivial. The question
is what are the relevant and desirable properties of the signal to
ensure that the resulting sound is as desired (eg, similar to a
real instrument). Slide 5 Applications Musical instruments Computer
games Sound effects for films Multimedia, computer system sounds
Mobile phones Speech synthesis Toys Effects Slide 6 Sound Synthesis
Plan Synthesis I: Fundamentals Synthesis II: Additive Synthesis
III: Filtering and distortion Synthesis IV: Other approaches
Post-processing, pitch correction (autotunes) Sound perception
Slide 7 Sound Synthesis Part I: Fundamentals Nicolas Pugeault
[email protected]
http://info.ee.surrey.ac.uk/Personal/N.Pugeault/ Slide 8 Lecture
Plan Introduction to sound synthesis Perception of sound Loudness
Pitch Timbre Sound synthesis Fundamentals Summary Slide 9 Sound
(contd) Sound is a pattern of compression and depression of the air
Record it using microphones Perceive it from our ears Generate it
by speaking or using speakers Energy per m2 decreases with the
square of distance... Slide 10 Sound is a waveform Sound is a
waveform, Can be reflected when hitting a non- transmissive surface
If the surface is flat, reflected in cohesive way Otherwise depends
on frequency and surface texture Sound proof studio wall, for
absorbing high frequencies Slide 11 Attributes of sound Sound
LoudnessTimbrePitch Temporal characteristic Spatial characteristic
Slide 12 The simplest sound: Pure tone Sinusoidal wave (440Hz)
Periode p=1/f0 Slide 13 Reminder: Fourier Transform Idea: All
functions can be decomposed in a (possibly infinite) sum of
sinusoidal functions of varying frequencies. Transforms a function
from time domain to frequency domain. Eg, right, for a square wave.
First component First two components First three components First
four components Slide 14 Loudness Often measured in decibels (dB)
R=20*log10(A/A0) A0 is a reference amplitude, often taken as the
threshold of audibility. Logarithmic perception of loudness. A
change in 6dB means a doubling of amplitude! Range of audibility:
~120dB (1 to 1million) Slide 15 Perception of Loudness Correlated
with amplitude. Here: constant frequency (f0=440Hz) Varying
amplitude (A = 0.2, 0.5 or 1.0) Slide 16 Loudness (contd) However
Perception of Loudness is frequency dependent. Sound X and Y have
the same amplitude, which is louder, X or Y? X (100 Hz, A=1) Y
(3,500Hz, A=1) Considering only amplitudes, sound Y should be the
same loudness as sound X. However, Y is louder than X. Why? Slide
17 Loudness (contd) Fletcher Munson (1933) Subjects listen to pure
tones Various frequencies amplitude inc. per 10dB Robinson &
Dadson (1956) more accurate Basis for standard ISO-226 Perceived
Loudness (Phons) 1 Phon = 1dB SPL @ 1kHz British Standard BS ISO
226 (2003) (source wikipedia) Slide 18 Loudness (contd) There is a
difference between sensory loudness and perceptual loudness!
(Emmet, 1992) For the design of a synthesiser with large dynamical
range, changing only amplitude is a poor choice since signal may
clip. Solution: use spectral variation: Broad spectrum will likely
result in a loud sound. Narrow spectrum will be perceived as quiet.
Slide 19 Perception of Pitch Frequency correlated with pitch Here:
3 examples of pure tones. What if sounds are more complex? Range:
20Hz- 20kHz Best acuity: 200Hz- 2kHz Slide 20 Pitch: Fundamental
& Harmonics Real sounds are not pure more complex! The ear
assumes that multiple frequency components form one sound.
Harmonically related -> fuse into single pitch at Fundamental
Frequency (f0 largest common divisor) Each sinusoid is called a
Harmonic partial of the sound (fk = N*f0) Slide 21 Fundamental
& Harmonics (2) Fundamental f0 First harmonic f1 = 2*f0 Second
harmonic f2 = 3*f0 Third harmonic f3 = 4*f0 Seventh harmonic f7 =
7*f0... Slide 22 Fundamental & Harmonics (3) The pitch is
correlated with the Fundamental frequency. Although in this example
the fundamental is missing, the pitch is the same. The timbre is
different. Slide 23 Timbre All those sounds have the same pitch
(A4, 440Hz) Flute A4 Tuning fork A4 Violin A4 Singer A4 They differ
in timbre. Slide 24 Defining Timbre Definition (American Standard
Association): That attribute of sensation in terms of which a
listener can judge that two sounds having the same loudness and
pitch are dissimilar. (ASA, 1960 ; Wikipedia, 2011) Has a
wastebasket quality (Dixon Ward, 1965) : What is neither loudness
nor pitch... Synonyms: Tone quality or colour, texture... Affected
by a sounds envelope. Slide 25 Timbre (contd) What physical
parameters relate to timbre? Static spectrum (transient) Envelope
of spectrum (transient) Dynamic spectrum (time-evolving) Phase This
list is not exhaustive. cf wastebasket quality! Slide 26 Timbre:
Static Spectrum (220Hz) Slide 27 Timbre: Envelope of Spectrum Slide
28 Timbre: Envelope (contd) Difference in envelope (same note,
440Hz fundamental) Top: Flute Bottom: Violin Envelope differs!
Conclusion: Envelope is instrument-specific. Flute Violin Slide 29
Timbre: Envelope (contd) Arrows indicate formants. This slide
indicates two speech vowels (i and u) Formants not only determine
timbre but helps distinguishing vowels. (used in speech
recognition) Slide 30 Timbre: Dynamic Spectrum Will those two
sounds have the same timbre? No, same average spectrum, but
different timbre! Difference: Top: original sound Bottom: time
reversed. Conclusion: Temporal variation of spectrum impacts
timbre! A B Slide 31 Timbre: Dynamic Spectrum (contd) Slide 32
Timbre: spectrogram Time (s.) Frequency (Hz) Slide 33 Timbre:
Dynamic Spectrum (contd) This slides shows the long term (average)
spectrum for two sounds (top: original and bottom: time reversed)
Spectrum is identical; timbre is totally different very misleading!
Conclusion: it is important to know how the spectrum evolves in
time. The timbre does not only depends on the harmonic structure
but on the way spectrum varies in time. A) Normal B) Time reversed
Slide 34 Time envelope (ADSR) Time Envelope (ADSR) Attack is the
time from nil to peak. Decay is the time from peak to the sustain
level. Sustain is the level during the main sequence of the sounds
duration, until key is released. Release is the time to decay from
sustain level to zero. Slide 35 Time Envelope (example) Slide 36
Example of the same sound with and without attack Attack cut at
0.7s. With (blue+green): Without (green): Slide 37 Timbre: Phase?
Sound A Sound B Are A and B of different timbres? Slide 38 Timbre:
Phase? Timbre depends (weakly) on phase relationship between
harmonics. BUT waveforms are totally different, magnitude spectra
identical, and timbre are (almost) identical! Conclusion: Human
hearing is not sensitive to phase differences. Sound A: Square
wave, fundamental 500Hz, 9 harmonics. Sound B: Square wave,
fundamental 500Hz, 9 harmonics, every second harmonic phase shifted
by 90 degrees. Slide 39 Summary 1: Loudness Control In order to
control loudness in synthetic sounds: Modify the spectral content:
more energy at high frequency louder (see right). Modify the
amplitude Higher amplitude louder Slide 40 Summary 2: Pitch Control
In order to control pitch in synthetics sounds: Modify the
fundamental frequency. High fundamental frequency high pitch.
Fundamental frequency Slide 41 Summary 3: Timbre Control In order
to control timbre in synthetic sounds, modify Spectral content
Spectral envelope Spectrum in time Spectrum evolution during
transient states Slide 42 Plan Introduction to sound synthesis
Perception of sound Loudness Pitch Timbre Sound synthesis
Fundamentals Summary Slide 43 Fundamental Definitions Computer
Instrument: An algorithm that realizes (performs) a musical event.
Unit Generator: A high-level building block in an instrument. Slide
44 Oscillator Basic waveform generator Abbreviations: EG Envelope
Generator LFO Low Frequency Oscillator VCA Voltage Control
Amplifier VCF Voltage Control Filter Slide 45 Abbreviations EG
Envelope Generator LFO Low Frequency Oscillator VCA Voltage Control
Amplifier VCF Voltage Control Filter Slide 46 Important Terms Two
types of synthesisers monophonicpolyphonic You can only play one
note at a time. If you play several keys together, only one note
will be generated no chords! You can play several notes at the same
time can play chords! Slide 47 Types of synthesis Sound Synthesis
Additive synthesis Distortion techniques Subtractive synthesis
Granular synthesis Analysis based Physical modelling Slide 48 Plan
Introduction to sound synthesis Perception of sound Loudness Pitch
Timbre Sound synthesis Fundamentals Summary Slide 49 Additional
Reading C. Dodge, C., & Jerse, T. A. (1997). Computer Music:
Synthesis, Composition, and Performance. Schrimer, UK. (see
chapters 2 and 4)
