Welcome to the
of Frans A.
I retired from
Technology, Applied Physics
Department, in 2004.
However, I am still engaged in
some interesting stuff, along with a special item for
children. Please, mouse click the topic you are
your convenience, PDF files of papers not easily
Bilsen 1966, Bilsen 1967, Bilsen
Ritsma & Bilsen
1970, Bilsen 1973, Bilsen &
Raatgever 1973, Bilsen
Raatgever 1983, Bilsen
& Dols 1995,
Bilsen 2001, Bilsen &
Raatgever 2001, Bilsen &
at Chantilly castle in 1993
occurs in free nature when the sound of a sound source
reaches the ear of an observer directly and, at the same time,
against a sound-reflecting surface. This phenomenon has been named
Repetition Pitch (RP), because the addition of a true repetition
original sound to itself is the basic requirement (Bilsen, 1966).
corresponds to the reciprocal value of the time delay
between the original and the repeated (reflected, delayed) sound.
RP is most salient when the original sound is wide band
and pitch-less itself (for example: white noise).
Probably the first written
report of the phenomenon dates from Christian
observed such a pitch in the sound from a fountain
reflected against the steps of a large stone staircase in the
of the castle of Chantilly in France (see Oeuvres
Vol.10, Correspondance no.2840, pages 570-571, see Gallica
). A similar example stems from the Mayan step pyramid in Chichen Itza
detailed explanation see RPglide).
might also be able to observe a gliding pitch when a plane flies
by moving one's head towards and from the ground. Or more
when one approaches a steam locomotive blowing off
music, the phenomenon is sometimes deliberately created by
means (delay and add) to superimpose a pitch or coloration
effect on the original music (see Flanging
and sound recording, the phenomenon often causes an
unwanted coloration of the original sound. Blind peoples might use
to locate obstacles by clicking the street surface with
their cane, thus producing a wide-band impulsive sound that is
reflected by an obstacle. Numerous
experiments in the past, in
the field of psychological and physiological acoustics, aimed at
understanding the perceptual and neurological processes
perception in general, RP in particular. Both temporal and
models of pitch extraction were proposed (see References).
Three key publications
Two-octave scale in repetition pitch from digital noise
added to itself, stretching from G2 (10.20 ms delay) to G4
- RPm Two-octave scale
with many mutually-equal-distant
repetitions added (named IRN by
1996), thus producing an
- Locanimat A
digital animation with intensified RP illustrating the
pitch or coloration due to a single sound reflection from the
- Locomovie Fragment taken from an
arbitrary movie showing a steam
locomotive passing by and producing a changing RP sound
at a (fixed) microphone,
- Chantilly Video of
at the staircase of the castle Chantilly. Note a rather
salient RP due
to mutually-equal-distant reflections (compare IRN),
- Chichen Itza Three sounds in
a handclap, the pyramid's response (from ocasa), and
synthesized RP glide following the pyramid's dimensions.
- Bilsen, F. A., and Ritsma, R. J.
“Repetition pitch mediated by temporal fine structure at
regions,” Acustica 19, 114-115. PDF
- Bilsen, F. A. (1977). “Pitch of
evidence for a ‘central spectrum’,” J. Acoust. Soc. Am. 61,
- Sayles, M., and Winter, I.M.
temporal representation of the delay of dynamic iterated
positive and negative gain by single units in the ventral
Brain Res. 2007.06.098
A dichotic or binaural pitch may
observed when continuous white noise is presented
by headphones to the left and right ear of a listener. Given a
particular interaural phase relationship between the left and
signals, a sensation of pitch
occurs. In other words, stimulation of either ear alone gives rise
the sensation of white noise only, but stimulation of both ears
together produces the pitch. Generally, a dichotic pitch is
somewhere in the head amidst or separate from the background
be more specific, the dichotic pitch is
characterized by three perceptual properties: pitch value, timbre,
in-head position (lateralization) of the pitch image. The first
binaural pitch phenomenon reported in the literature is the
(HP) (Cramer and Huggins, 1958). In this case, the interaural
relationship consists of a rather sharp phase shift over 2 pi
in a narrow-band frequency region of the white-noise spectrum. The
sensation is of a fluctuating pure tone. Probably the strongest
dichotic pitch ever is created by having several
phase-shift regions. It is therefore called multiple-phase-shift
(MPSP, Bilsen, 1976; see also sirl
for a similar stimulus).
Experiments on dichotic pitch were motivated by the
study of pitch in general and of the binaural system, being
and separation of sound sources (see cocktail
). Various models were developed in the past.
the so-called CAP-CS model seems successful in predicting
pitch value and pitch-image position (see References).
* sound tracks taken
from the audio compact disc
with booklet "Demonstrations of
Pitch" by F.A.
Bilsen and J. Raatgever (Delft, 2002),
- MPSP+ Two-octave scale in MPS
pitch, stretching from G2 (98 Hz) to G4 (392 Hz). The pitch
perceived in the center of the head,
- MPSP- Two-octave scale in the
same pitch range. Due to the extra interaural phase shift of pi
radians, the pitch image now is perceived off center,
- HP+ Two-octave scale in Huggins
pitch (HP) stretching from C4 (262 Hz) to C6 (1047 Hz). This
a fluctuating pure tone in head centered,
- HP- Two-octave scale in the same
range. Again, due to the extra interaural phase shift of pi
the pitch image now is perceived off center.
* It may be evident that
dichotic-pitch stimuli should be listened to properly with
Tracks 1 - 62 of audio
compact disc (DP_wma)
- Fourcin, A.J.
(1970). “Central pitch and auditory lateralization,” in Frequency
Periodicity Detection in Hearing, ed. R. Plomp and G. F.
Smoorenburg (A. W. Sijthoff, Leiden), pp. 319-328.
- Raatgever, J.,
and Bilsen, F. A. (1986). “A central spectrum theory of binaural
Evidence from dichotic pitch,” J. Acoust. Soc. Am. 80, 429-441.
- Bilsen, F.A., and
Raatgever, J. (2000). “On the dichotic pitch of simultaneously
interaurally delayed white noises. Implications for binaural
Acoust. Soc. Am. 108, 272-284.
One of the problems with
hearing aids is malfunctioning in situations with disturbing
noise like, for example, in a cocktail-party or meeting-like
Therefore, around 1983, I proposed a project at the Delft
aiming at a new type of hearing aid that would enable
peoples to focus on a
particular voice amidst of other disturbing voices and/or noises.
general, three strategies
seem feasible: 1) the use of two identical conventional hearing
provided that both ears have degraded about equally, 2) the use of
conventional hearing aid supplied with binaural-like signal
processing, and 3) the use of one or two conventional hearing aids
a strong directional microphone. Given the knowledge and
available in the TUD
, the latter option was chosen and this has
resulted in the "hoorbril
pair of spectacles with an array of
microphones mounted either on the legs (endfire array) or on the
itself above the glasses (broadside array). Financial support was
supplied by the Dutch Organization for Scientific Research (NWO)
the Philips Company. Today, the company Varibel
produces and sells
endfire principle. See also Babble
- Bilsen, F.A., Soede, W., and Berkhout, A.J. (1993).
“Development and assessment of two fixed-array microphones for
aids,” J. Rehab. Res. Developm. 30, 73-81.
- Soede, W., Berkhout, A.J., and Bilsen, F.A. (1993).
“Development of a directional hearing instrument based on
Acoust. Soc. Am. 94, 785-798.
- Soede, W.,
Bilsen, F.A., and Berkhout, A.J.
(1993). “Assessment of a directional microphone array for
listeners,” J. Acoust. Soc. Am. 94, 799-808.
Acoustics and biophysics
Here you will find a list of publications in english by coworkers of
former research group named "Biologische
Natuurkunde" (Biophysics, from 1967
headed by Prof.dr. G. van den Brink) and re-named "Akoestische
Perceptie" (Perceptual Acoustics, untill 2002 headed by
F.A. Bilsen) on acoustical topics,.
In classical mechanics, the
of rigid bodies is generally
described by two analogous vector equations: F
of the center of mass, and M
for rotation around the center of mass, with F
the total external force, p
the momentum (dutch: impuls
the moment of forces
(koppel of krachtmoment
the angular momentum (impulsmoment
we consider the
intriguing movement of
the so-called tippe
or Kelvin top after its inventor Lord Kelvin
(Sir William Thomson). Such a top essentially consists of a
body and a
cylindrical stem, with the center of mass displaced from the
the sphere. After having been put into rotation around its
axis of symmetry vertically, the top gradually changes its
flips over into a stable rotation on and around the stem. We have
conclude that the rotation has changed sign, such
the angular momentum
still has its
position. Further, the center of gravity has moved upwards,
the cost of a decrease in magnitude of L
behavior is explained by the action of a small friction
at the contact point
of the top with the ground surface. Many publications in the past
been devoted to the explanation of the complex
movement of the tippe top. Here we propose a qualitative explanation
using the above equations
only. For further details and demonstrations see TippeTop1
Enjoy a movie (Bilsstadt1) or slide
show (Bilsstadt2) of our model train setup.