News 2008

Didge(R)Evolution


After 6 years of private theoretical and experimental (low budget) research driven by curiosity and the longing after individually playable desired instruments a highlight of the common Didjeridu research project (Geipel / Reimer) is reached now.

Many Didjeridu players from all over the world want to know whether it is possible to create an instrument after its individual desired conceptions. Since some years that is possible with our Computer-Aided-Didjeridu-Sound-Design-tools (CADSD), but required much experience and simulation time, since many interior forms had to be adjusted and varied by hand, to get the desired relevant impedance and sound spectra.

So far it was not possible to find the interior forms for desired spectra in a more efficient and automatically way. In order to reach this, I started at the beginning of 2008 the project „Didge(R)Evolution“- the application and advancement of nature modelled evolution algorithms for the generation of desired forms from practically immense, infinite large variety of possible forms.

The current project highlight is a simulation system, which is able to generate desired instruments on basis of an advanced high performance simulation model of the Didjeridu acoustics and using new Didjeridu specific directed-evolution-methods. It runs like a “living evolution system” in which special instruments with many specific parameters can quasi “breed”. The so created interior forms often looks similar the cross-sectional contours of good termite-carved instruments, with the difference, that the method is able to generate also forms which do probability not occur in nature.

Frank Geipel, 3th October 2008



 
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Simplified description of the CADSD based Didge(R)Evolution software

Since only few Didjeridu building interesting people have experiences with mathematical modelling, programming and physical theories, here a simplified description of the Didge(R)Evolution software:

Before the program can take up its work, a goal of a sound- and an impedance spectrum exact as possible must be defined. That can be momentary up to 20 different characteristics.

Imagine you then, we create (program) virtual termite swarms, whose single termites have individual abilities to form Didjeridus with special characteristics. In the next step the size and number of this virtual termite swarms have to be fixed - in our animated example is it only 1 swarm with 512 termites.

With the start of the program each individual termite takes up its work and eats (first times completely randomized) its own Didjeridu within the spatial delimitation of the virtual blank tree. After some seconds the first 512 instruments are finished.

Now each individual instrument is tested how well it fulfils the given goal characteristics. The termites, which were most successful, may reproduce and pass their genetic information on to a new termite generation. The others become extinct. Additionally, similarly as in nature, coincidental mutations are produced, which change the individual characteristics of individual termites. Thus the first generation is terminated.

In the second generation the descendants as well as its relatively successful parents and mutated brothers and sisters eats out again 512 Didjeridus from virtual blank trees again randomized however with improved individual characteristics to reach the goals. Afterwards again all instruments are tested. The successful termites of the swarm may reproduce again, while the remainder becomes extinct.

This evolutionary cycle is repeated until a virtual Didjeridu was produced with all defined goals in the best possible way fulfilled and no evolutionary progress is reached - in the example visibly as the red line. Usually after 150 to 400 generations this is the case.

In order to produce outstanding and special instruments with this directed evolution method, the know-how of the “Didjeridu breeder” to formulate the goals is very important. Extensive knowledge about the interactions of most diverse intrinsic resonance pattern with different play techniques on the effects of the sound spectra are of crucial importance, but also extensive building and playing experiences. The results depend on the quality of the defined goals.

Frank Geipel, 2th November 2008

History
Common Didgeridoo research project:

To reach and inspire the world-wide player community interested in the Didjeridu, we had decided (2003) not to publish in scientific specialized media. From that surrounding field in the meantime cases exists, where partially information from our project without indication of source is used and/or existing sources are listed incompletely.

June 1998
Knowledge, that the sound characteristics are determined substantially by the interior forms (by termites coincidentally eaten or handmade).
First experiments with sliding elements in didjeridus (handmade).
(Reimer)

January 1999
Development of the “Test-A-Doo“ for the experimental examination of different interior forms during playing.
(Reimer)

June 2001
Presenting the website “Test-A-Doo”.
(Reimer)

May 2003
Use of the transmission line method to simulation of impedance spectra of complex Didjeridu interior forms for the determination of playable overblows (toots).
(Geipel)

June 2003
Start of cooperation Reimer/Geipel

August 2003
Development of methods for the simulation of sound spectra of complex Didjeridu interior forms and the first CADSD software (Computer-Aided-Didjeridu-Sound-Design). Explanation of singing harmonics and heterodyne amplification.
(Geipel)

May 2003
Development of the water level method for the reconstruction of cross-sectional contours of interesting Didjeridu interior forms.
(Reimer)

November 2003
First German expenditure of the book „The Didgeridoo phenomenon “and explanation of the interior form dependence of sound development in Didjeridus.
(With chapters from Reimer „Dem Wunschklang auf der Spur“ und Geipel „CADSD – Simulation von Klangspektren komplexer Didgeridoo-Innenformen“)

October 2003
Extension the website “Test-A-Doo” to “didgeridoo-physik.de”
(Reimer / Geipel)

April 2004
Article in the “Didgeridoo & CO magazine”
Physics and construction / The digitally didge
(Geipel)

September 2004
Building of prototypes according to bag method (similar Hempstone Didges) for the experimental verification of CADSD designed Didjeridus
(Reimer)

October 2004
First English expenditure of the book „The Didgeridoo Phenomenon“.
(With chapters form Reimer „Seeking the desired sound“ and Geipel „CADSD – Simulation of sound spectra of complex Didgeridoo interior forms“)

November 2004
Study and explanation of the harmonic wobble effect during Yidaki playing with NEAL style.
(Geipel)

September 2007
Study and explanation of the heterodyne amplification during Mago playing with WAL style.
(Geipel)

March 2008
Installation of new knowledge into the first high performance CADSD version.
(Geipel)

May 2008
Start of the Didge(R)Evolution project.
(Geipel)

September 2008
First directed evolution of Didjeridus with free definable physically possible sound and play characteristics.
(Geipel)


Our special thanks regard to the north-Australian indigenous people of the origin areas of the Didjeridu, their fascinating playing techniques and talents in Yidaki- and Mago-crafting. The musical and emotional experiences in that field inspired us to advance this private research project. There is still much to discover.

Frank Geipel, Kay Reimer
5. October.2008

Physics of the Didgeridoo  

DThe x-ray photos by Johannes are unique! Have a look!!!!

Johannes Schildkamp Kay Reimer / 13.11.04               zurück   This Website lives on the cooperation of non-commercially oriented Didgeridoo-builders. They all have in common the search for deeper knowledge that might shed some light on the complex coherences of the production of sounds of the didgeridoo, and the willingness to share parts of this knowledge with the public. One of those is Johannes Schildkamp, known by many in the scene by his method of didge-boring. Some time ago we decided to closely connect our websites, which means that parts of the contents of www.yedaki.de can now be reached directly via www.testadoo.de / www.didgeridoo-physik.de and, in the near future, vice versa. We are looking forward to the x-ray photos he is preparing at the moment.   Improved method of measuring Kay Reimer / 14.10.04                back Now inner shapes of didgeridoos can be measured more precisely. This relatively simple gadget works on the principle of communicating pipes and also allows the measuring of bent didgeridoos. The didgeridoo is being filled step by step with water, the filling level can be read off outside the instrument. The amount of filling can be dosed by a pump combined with a clock timer. Thus the amounts and levels of filling plus the angle of the measured part are aquired to calculate the inner shape. On these photos you can see the measuring of a new CADSD-prototype. The intention here was to identify possible errors of the planned inner shape. This is important to ensure that the prototype exactly matches the afor simulated shape. If I then like the sound I get when playing the prototype, I can confidently transfer that shape to a raw log of noble wood to realise my desired didge. A further chapter to this should be about the fine tuning of the raw log to influence the resonances of the wood. But we will come to that later...       Overtone wobbles Frank Geipel / 11.11.2004                     back With the sound of some very rare didgeridoos comes a distinct "wobble" (kind of vibrato) between certain overtone-frequencies, especially when being played with dynamic traditional techniques. These instruments are quite rare, like e.g. the "E" owned by Sven Molder or the Datjirri-"F-F#" owned by Frank, as shown in the gallery. What is the physical reason for this effect? The vibrating air column of a didgeridoo shows several resonances depending on the inner shape, these can also be played as toots (white peaks in the figure below). With these resonance frequencies the didgeridoo is bound to oscillate. An harmonic overtone of the basic drone occuring to fall on one of those resonance frequencies will be amplified and is then clearly perceptible as "singing" tone. (For further interest in this subject I recommend the book The didgeridoo phenomenon“.) But what exactly is the precondition for a didgeridoo to be able to "wobble" between the 5th and the 6th harmonic overtone (6th and 7th multiples of the basic frequency)? In the case of the instrument depicted by the figure below, a pronounced resonance of the the oscillating air column can be detected, lying about 10Hz below the 5th and about 10Hz above the 6th harmonic overtone frequency. If this didgeridoo is played dynamically, an unstable wobble-state is acquired, meaning that by a short push of the fundamental the 6th overtone will jump 10Hz higher into the resonance present at that peak, hence being amplified for a short period. As this state is unstable, the fundamental will fall back, lowering the 5th overtone by 10Hz into the resonance peak existing there, thus amplifying again the according overtone for a short period. This effect will occur 5-10 times per second, hence a distinct "wobbling" (vibrating, singing) overtones can be perceived. After further refinement of the CADSD-method it is now possible for us to project and build instruments showing these overtone "wobble" abilities. FFT taken from our fibre-glass "E" horizontal axis: Frequency in [Hz] - vertical, from top to bottom: time red: loud (distinctly) perceptible partial tones yellow: medium perceptible partial tones green: quiet perceptible partial tones Overtone wobbles from 470-600 Hz 5th harmonic overtone (6th multiple of the basic tone frequency) at about 498 Hz (resonance frequency to the left of it at about 485 Hz) 6th harmonic overtone (7th multiple of the basic tone frequency) at about 580 Hz (resonance frequency to the right of it at about 595 Hz) Sound example FFT taken from Svens "E-Yidaki" horizontal axis: Frequency in [Hz] - vertical, from top to bottom: time red: loud (distinctly) perceptible partial tones yellow: medium perceptible partial tones green: quiet perceptible partial tones Overtone wobbles from 490-590 Hz 5th harmonic overtone (6th multiple of the basic tone frequency) at about 500 Hz (resonance frequency to the left of it at about 490 Hz) 6th harmonic overtone (7th multiple of the basic tone frequency) at about 580 Hz (resonance frequency to the right of it at about 590 Hz) Sound example

Making CADSD-Prototypes using fibreglass components Kay Reimer / 12.9.2004              back Its quite simple to quickly check a few basic shapes using the Testadoo, but its very hard to achieve complex interior shapes with it. To get suitable test instruments for calculated CADSD results I use the method described first-time by the inventors of the hemp-didgeridoos. The method is simple as well as ingenious - a sack resembling the desired interior shape is filled up with sand and sprayed on with a mash of hemp fibres and water. After hardening the sack is removed - and here goes your didge. Cool! Ansgar Stein has successfully transferred this method to fibreglass didge making. From him I got the first tips which I modified due to the precise requirements for making CADSD prototypes. The new version of CADSD now automatically calculates the precise measurement of the sack for the interior shape. This is transferred 1:1 into a graphic application and printed. The template is then copied on two layers of non elastic fabric, sewn precisely and cut out. To reduce the impact on the material and also to avoid inconsistencies caused by the extensility of the fabric I use rice instead of the heavy sand as filling material. A two-joint attachment also avoids longitudinal extension. Then the sack is coated step by step first with seperating agents, followed by synthetic resin and fibreglass matting up to a wall thickness of 6 to 20mm. After hardening the sack is removed and the new prototype is cut to the final length. The playing and sound capabilities now can be checked and compared via FFT with the calculated overtone and resonance spectra. The accuracy of the making process can easily be verified using my improved method of measuring interior shapes. Although these instruments sound very good themselves, I mostly use them as a preparation for the more time consuming making of CADSD- wood instruments (e.g. for Franks current overtone-wobble-project...). (As you can see with Ansgar Steins fibreglass instruments, these didges are ideal for travelling and life performance. He recently made a fibreglass-version of his favorite Didge, using the measuring method)

New CADSD Didgeridoos! Frank Geipel / 12.08.2004               back The computer-aided-sound-designed F/F-Twins are ready! Although I know by my simulating method about the intended sound and playing characteristics, it is always a good experience to really hear and play the ready made instruments. Both Instruments are made from heavy and hard (hopbeam). Both are on F and have the first overblown one octave above. But the playing characteristics are totally different... and hard to describe. 1) Length: 157 cm, weight: 4,6 kg, material: (hopbeam), Inner diameter mouthpiece: 28-29 mm iInner diameter bell: 80-100 mm oval Outer diameter bell: 110-130 mm, Sound: open, resonant, enhanced/singing 2nd harmonic overtone, Response: excellent, Back pressure: medium Basic tone: F, 1st Overblow: F, 2nd Overblow: C  Sound example (played by Frank) Sound example (played by Sven Molder) 2) Length: 152 cm, weight: 5,0 kg, material: (hopbeam), Inner diameter mouthpiece: 28-29 mm, Inner diameter Bell: 85-125 mm heart-shaped, Outer diameter Bell: 110-150 mm, Sound: direct, dry, pronounced 2nd harmonic overtone, singing 5th harmonic overtone Response: excellent Backpressure: high Basic tone: F, 1st Overblow: F Sound example (played by Frank) Sound example (played by Sven Molder) back to top