sound synthesis
Download
Skip this Video
Download Presentation
Sound Synthesis

Loading in 2 Seconds...

play fullscreen
1 / 41

Sound Synthesis - PowerPoint PPT Presentation


  • 158 Views
  • Uploaded on

Sound Synthesis. Part II: Oscillators, Additive Synthesis & Modulation. Plan. Simple Oscillator (wavetable) Envelope control Simple Instrument (Helmholtz) Additive Synthesis Modulation Summary. AMP. FREQ. PHASE. WF. Simple Oscillator. Oscillator 3 strategies.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Sound Synthesis' - tannar


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
sound synthesis

Sound Synthesis

Part II: Oscillators, Additive Synthesis & Modulation

slide2
Plan
  • Simple Oscillator (wavetable)
  • Envelope control
  • Simple Instrument (Helmholtz)
  • Additive Synthesis
  • Modulation
  • Summary

AMP

FREQ

PHASE

WF

simple oscillator
Simple Oscillator

Oscillator

3 strategies

Mathematical equation based oscillator

Wavetable oscillator

IIR-Based oscillator

  • Solve math function for each sample
  • Ex: y = sin(x)
  • + Accurate
  • Inefficient
  •  Non real-time applications
  • Pre-computed and stored in memory
  • + Fast (Look-up table)
  • Memory

Unstable filter that generates waveform of desired amplitude and frequency.

+ Fast

+ Memory efficient

 Sound synthesis

wavetable oscillator
Wavetable Oscillator
  • Example of a wavetable (N = 16)
  • Store N values sampled over one cycle
  • Phase increment: SI=N f0/fs
wavetable oscillator example
Wavetable Oscillator (example)
  • Parameters
    • N = 16
    • F0 = 220
    • Fs = 1kHz
    • SI = 16 * 220/1000SI = 3.52
  • Increase quality:
    • Increase sampling rate
    • interpolate
wavetable oscillator distortions
Wavetable Oscillator Distortions
  • Quantization:Eg, pure tone F0=440Hz, Fs=8,192Hz
    • Truncate N=16
    • Truncate N=32
    • Truncate N=512
  • Interpolation: truncate, mean, linear
  • Aliasing
wavetable oscillator interpolation
Wavetable OscillatorInterpolation
  • Truncation (0th level interpolation)
wavetable oscillator interpolation 2
Wavetable Oscillator Interpolation (2)
  • Rounding (slightly better 0th order)
wavetable oscillator interpolation 3
Wavetable Oscillator Interpolation (3)
  • Linear (First order interpolation)
wavetable oscillator interpolation 4
Wavetable Oscillator – Interpolation (4)
  • Quadratic (Second order interpolation)
wavetable oscillator interpolation 5
Wavetable Oscillator Interpolation (5)
  • Cubic (Third order interpolation)
wavetable oscillator interpolation 6
Wavetable Oscillator Interpolation (6)
  • Signal to (interpolation) Noise Ratio (SNR)(eg, pure tone F0=220Hz, Fs=8,192Hz)
    • Truncation: SNR = 6 k – 11 dB
    • Rounding: SNR = 6 k – 5 dB
    • Linear: SNR = 12 (k – 1) dB(Moore, 1977; Hartman, 1987)(k = log2(N) and N is the table length)
  • Conclusion: For increasing quality, increase number of samples, and use interpolation.
wavetable oscillator interpolation 7
Wavetable Oscillator Interpolation (7)
  • Pure tone F0=440Hz, Fs=8,192Hz
    • Truncate N=16
    • Truncate N=32
    • Truncate N=512
wavetable oscillator aliasing
Wavetable Oscillator – Aliasing
  • Aliasing: One of the biggest problem for modern digital sound synthesisers (sampling freq fs=48kHz, Nyquist freq fn=fs/2=24kHz).
  • How to avoid aliasing?
    • Storing a band-limited version of the waveform in the table (in memory)
    • Or, generate an aliasing-free signal from frequency-limited Fourier series representation.
aliasing 2
Aliasing (2)
  • Several sinusoids can fit a set of samples.
  • Aliasing when sampling rate is low! Example:
    • Signal:f0 = 0.9Hz(red)
    • Sampling at:fs = 1Hz, Nyquist freq fn = 0.5Hz
    • perceived fa=|n*fs-f0|=0.1Hz(blue) (n such that fa < fn)
aliasing 3
Aliasing (3)
  • Square wave, 563 Hz fundamental, 48kHz sampling rate.

Generated using “perfect” square waveform

Generated using a limited Fourier series.

slide17
Plan
  • Simple Oscillator (wavetable)
  • Envelope control
  • Simple Instrument (Helmholtz)
  • Additive Synthesis
  • Modulation
  • Summary

AMP

FREQ

PHASE

WF

time envelope 1
Time Envelope (1)
  • ADSR Envelope
    • Attack
    • Decay
    • Sustain
    • Release
  • Important is:
    • Duration
    • Shape
      • Linear
      • Exponential
      • Other (functional, table)
linear vs exponential envelope
Linear vs. Exponential Envelope

A) Linear

B) Exponential

  • Recall:“amplitude perception is (nearly) logarithmic”
    • linear decay  logarithmic (perceived) fading
    • Exponential decay  linear (perceived) fading
  • Note: Exponential decay never reaches zero  set min value
oscillator as an envelope generator
Oscillator as an Envelope Generator

A

fm

  • Advantages:
    • wavetable interpolated shape.
    • Easy encoding of several repetitions.
  • Drawback:
    • attack and decay times are affected by overall duration!
  • Alternative:
    • interpolated function generator

fc

slide21
Plan
  • Simple Oscillator (wavetable)
  • Envelope control
  • Simple Instrument (Helmholtz)
  • Additive Synthesis
  • Modulation
  • Summary

AMP

FREQ

PHASE

WF

simple instrument
Simple Instrument
  • Helmholtz model
    • Waveform
    • Constant frequency
    • Envelope
  • Envelope feeds varying amplitude to the oscillator.

AMP

DURATION

ATTACK

DECAY

ASD Envelope

FREQ

AMP

PHASE

simple instrument 2
Simple Instrument (2)
  • Envelope generator used as a signal processor.
  • Oscillator feeds varying amplitude to the envelope generator.
  • Allows to process the amplitude of a natural (recorded) sound through an envelope.

AMP

FREQ

PHASE

DURATION

AMP

ATTACK

DECAY

ASD Envelope

limitations of the simple instrument
Limitations of the Simple Instrument
  • Helmholtz model
    • Waveform
    • Constant frequency
    • Envelope
  • Limitations:
    • Amplitudes of all spectral components vary simultaneously.
    • All spectral components are perfect (integer) harmonics.
  • ... unlike real sounds!

AMP

DURATION

ATTACK

DECAY

ASD Envelope

FREQ

AMP

PHASE

slide25
Plan
  • Simple Oscillator (wavetable)
  • Envelope control
  • Simple Instrument (Helmholtz)
  • Additive Synthesis
  • Modulation
  • Summary

AMP

FREQ

PHASE

WF

additive synthesis
Additive Synthesis

FREQ

FREQ

FREQ

+

additive synthesis 2
Additive Synthesis (2)
  • Analysis: Frequency and amplitude envelopes can be obtained from analysis (spectrogram)
  • Flexibility: Virtually any sound can be synthesised.
  • Allows for the generation of new, natural sounding functions.
  • Quality: Can realize sounds that are “indistinguishable from real tones by skilled musicians” (Risset, Computer Study of Trumpet Tones, 1966)
additive synthesis 3
Additive Synthesis (3)
  • But...
    • Require large amount of data to describe a sound
      • Each oscillator requires two functions
    • Functions are only valid for limited rangeof pitch and loudness!
      • Analysis for a given pitch and loudness will not give the same timbre when extrapolated for different pitch and loudness.
  • Requires very large library of function sets!
  • Just too much control?
slide30
Plan
  • Simple Oscillator (wavetable)
  • Envelope control
  • Simple Instrument (Helmholtz)
  • Additive Synthesis
  • Modulation
  • Summary

AMP

FREQ

PHASE

WF

modulation
Modulation
  • Modulation:“Alteration of amplitude, phase or frequency of an oscillator, in accordance to another signal” (Dodge & Jerse, 1997)
  • Vocabulary:
    • Carrier oscillator: modulated oscillator
    • Carrier wave: modulated signal (prior to modulation)
  • Spectral components of modulated signal:
    • Carrier components: come only from carrier
    • Sidebands: come from both carrier & modularion
amplitude modulation
Amplitude Modulation
  • Carrier:
    • Frequency: fc
  • Modulating
    • Frequency: fm
    • Amplitude m*AMP
  • Modulation index: m
    • m=0 no modulation
    • m>0 modulation
    • m=1 full modulation

m*AMP

AMP

fm

+

fc

AMP

amplitude modulation 2
Amplitude Modulation (2)
  • Carrier frequency fc
    • Unaffected by modulation index
  • Sidebands fc+/-fm
    • Amplitude m/2*AMP
    • Energy split equally between lower/higher
    • When m=1, sidebands 6dB below carrier
  • Perception
    • If fm>10Hz -> two tones, additional loudness.
    • If fm<10Hz -> tremolo

Amplitude

AMP

m/2*AMP

fc-fm

fc

fc+fm

Frequency

Pure tone fc=220Hz

Tremolo fc=220Hz, fm=6Hz, m=1

ring modulation
Ring Modulation

A

A

A

fm

fc

fm

  • Modulation is applied directly to carrier’s amplitude.
    • A=0  no signal!
  • Alters frequency!
  • If both sinusoidals:
    • Only sidebands:fc-fm and fc+fm!
    • Amplitude A/2
  • Eq. to signal multiplication

fc

*

Amplitude

A/2

fc-fm

fc

fc+fm

Frequency

vibrato modulation
Vibrato Modulation
  • Modulating signal applied to the carrier’s frequency.
  • “Slight wavering of pitch”
  • Pitch varying between fc-v <= fv <= fc+v
  • Average is <fv> = fc
  • Eg, fc=220Hz
    • Pure tone
    • Vibrato fv=6Hz, v=0.05fc

v

fm

fc

+

A

fv

slide38
Plan
  • Simple Oscillator (wavetable)
  • Envelope control
  • Simple Instrument (Helmholtz)
  • Additive Synthesis
  • Modulation
  • Summary

AMP

FREQ

PHASE

WF

additional reading
Additional Reading
  • C. Dodge, C., & Jerse, T. A. (1997). Computer Music: Synthesis, Composition, and Performance. Schrimer, UK.(see chapter 4)
slide40

v

fc

fm

AMP

DURATION

ATTACK

DECAY

ASD Envelope

+

fv

AMP

slide41

AMP

DURATION

ATTACK

m*AMP

ASD Envelope

fm

AMP

+

fc

AMP

ad