Model-Based Synthesis of the Clavichord Vesa Vlimki 1 , Mikael - - PowerPoint PPT Presentation

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Model-Based Synthesis of the Clavichord

Vesa Välimäki1, Mikael Laurson2, Cumhur Erkut1, and Tero Tolonen1

1Helsinki University of Technology,

Laboratory of Acoustics and Audio Signal Processing (Espoo, Finland)

2Sibelius Academy, Centre for Music and Technology

(Helsinki, Finland)

ICMC 2000, Berlin, August 2000

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• 1. Introduction
• 2. Acoustics of the Clavichord
• 3. Synthesis Model
• 4. Musical Example
• 5. Conclusions

Model-Based Synthesis of the Clavichord

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• 1. Introduction
• The clavichord is one of the oldest musical instruments
• Sound is pleasant but quiet

– Maximum SPL only about 50...60 dB

• Only useful in intimate performances
• We propose a digital synthesis method to generate

clavichord tones

• SPL can be amplified using the volume knob

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• 1. Introduction (2)
• Mikael has a clavichord

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• 1. Introduction (3)
• The instrument used in our measurements (Heugel, Paris)

Sound example: A short excerpt

• f a piece by

J.S. Bach

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• 2. Acoustics of the Clavichord
• String is excited with a simple lever mechanism
• Enables mechanical aftertouch

(from T.D. Rossing, “The Science of Sound”, 2nd Ed. Addison-Wesley, 1990)

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• 2. Acoustics of the Clavichord (2)
• Waveform shows the attack transient and a noise

burst at the end (A3, 197.5 Hz)

• Sound example: this signal 3 times

0.5 1 Time (s)

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• 2. Acoustics of the Clavichord (3)
• Pitch decays during the attack

– Player’s hand probably affects the string tension – Contribution of tension modulation effect is weak

• Should be accounted for in sound synthesis

0.5 1 197 198 199 200 Frequency (Hz) Time (s)

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• 2. Soundbox
• The bridge was

excited with an impulse hammer

– Most prominent modes can be found – Excitation point was varied to see how mode amplitudes change

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• 2. Soundbox (2)
• Modes are

excited in a different way

• The soundbox

response is an essential part of clavichord tones

• Sound example:

1) Original 2) Fade-in to avoid metallic attack (Played 2 times)

100 200 300 400 500 20 40 60 Magnitude (dB) 100 200 300 400 500 20 40 60 Magnitude (dB) Frequency (Hz)

High end Low end

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• 3. Synthesis Model
• Commuted Waveguide Synthesis

(Smith, ICMC’93; Karjalainen et al., ICMC’93)

– Partials are extracted from recorded tones (inverse filtering or subtraction of a sinusoidal model) – These are excitation signals for a string model

• Currently, we have a fully automatic analysis (Erkut

et al., 2000, AES 108th Conv.)

• Sound example

– A chromatic scale “without partials” but including the soundbox sample

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• 3. String Synthesis Model

F( z) D e la y l i n e H l ( z) Input O ut p u t Loo p F i l t e r F ra c t i

• n

a l D e lay

Fundam en tal f r e q uency Decay r a t e

• Invented by Jaffe and Smith (1983) based on the

Karplus-Strong algorithm (1983)

• Can be derived from the solution of the wave

equation (Smith, CMJ 1992)

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• 3. Modified String Model

F( z) D e la y l i n e H l ( z) Input O ut p u t

A t tack sharpness

• Modification to control the sharpness of the attack

– Controls the contribution of the hammer noise – Needed particularly at high frequencies

• A sharper attack is obtained when gdir > 1

gd

ir

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• 3. Modified String Model (2)
• Sound example (A4, 392 Hz)

– gdir = 1.0 – gdir = 2.0 – gdir = 3.0 – gdir = 4.0

(played 2 times)

F( z) D e la y l i n e H l ( z) Input O ut p u t gd

ir

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• 3. Model Structure
• Two string models coupled together for each string
• Resonators simulate the ringy modes of the soundbox

In

1 i

g ) (

1 z

S ) (

2 z

S ) (

1 z

R ) (z RK Out

2 i

g

1

• g

2

• g

2 1

c

...

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• 3. It’s Not Really Physical Modeling
• Several samples are used
• 1. Excitation

– Processed recordings – Fed into the string models

• 2. Hammer noise for ends of notes

– Can be extracted from recordings of very long tones

• 3. Soundbox response

– Processed impulse response of the soundbox – Triggered at a low level for each note

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• 3. Implementation
• Implemented using ENP

– Extended standard musical notation and synthesis control (see Laurson et al., ICMC’99)

• Real-time synthesis with 6-voice polyphony on a

Macintosh G3 laptop

• Recently, tension modulation nonlinearity was included

(Tolonen et al., 2000)

– Produces “less synthetic” sound

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• 4. Musical Example
• Renaissance music produced by Mikael Laurson:

Guillaume Dufay (1400-1474), “Par le regard de vos beaux yeux”

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• 5. Conclusions
• A simple clavichord synthesis model was proposed
• Combines Commuted Waveguide Synthesis and

Sampling

– String synthesis using coupled digital waveguides – Repreduction of hammer noise and soundbox responses using special and processed recordings

• Demos and musical examples will be available at:

http://www.acoustics.hut.fi/~vpv/publications/icmc00.htm