Translating the human hair surface state into
sound
Authors: Mariko NOMURA1, Hiroaki IDE2, Akiko KAMIGORI1, Damien VELLEMAN1,
Frederic FLAMENT PhD3
(1) Nihon L’Oréal Research and Innovation, Kawasaki, JAPAN
(2) EL PRODUCE Inc., Ide Sound Institute, Tokyo, JAPAN
(3) L’Oréal Research and Innovation, Chevilly-Larue, FRANCE
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Translating the human hair surface state into sound
Authors: Mariko NOMURA1, Hiroaki IDE2, Akiko KAMIGORI1, Damien VELLEMAN1, Frederic
FLAMENT PhD3
(1) Nihon L’Oréal Research and Innovation, Kawasaki, JAPAN
(2) EL PRODUCE Inc., Ide Sound Institute, Tokyo, JAPAN
(3) L’Oréal Research and Innovation, Chevilly-Larue, FRANCE
Introduction:
The surface of the hair shaft is regularly submitted to frictional processes (shampooing, brushing,
combing, etc.) that progressively damage hair cuticles over time, assuming an average 1cm/month growth
rate (1). The tip of a 36 cm long hair is therefore 3 years “old” and bears witness to structural assaults that
occurred during this period. These events are amplified by frequent, careless brushing, often on a daily
basis, and too intense, inappropriate or frequent bleaching and perm, which cause the cuticle scales to lift
up (2-6). Such surface “hooks” increase friction. Due to the direction of the cuticle scales along the hair
shaft, the coefficient of hair surface friction depends on the direction of the induced movement, i.e. root to
tip or tip to root, the latter being higher. The numerous techniques that record hair (or wool) frictional
properties have been extensively reviewed (7). The recent availability of highly sensitive equipment (see
below) allowed us to record the tiny irregularities of the hair surface using a manually driven probe sliding
along the hair shaft in a given direction. The recorded signal can then be translated into sound to be heard
by consumers and/or hair professionals. The preliminary results of this new approach and its possible future
development are the subjects of this oral presentation.
Objectives
The objectives of this study were to, i) assess in vitro, the ability (sensitivity) of currently
available instruments to record the frictional state of differently damaged hair swatches and ii) develop an
algorithm that transforms the recorded frictional forces into sound which can be perceived by humans (i.e.
between 20 Hz to 20 KHz). This process, called “sonification” (8), transforms raw data into non-verbal
acoustic signals (e.g. Geiger counter and wind-bells). In short, this approach transforms a physical signal
into a sound heard by the consumer or the hair professional that translate the hair surface status, i.e.
whether it is altered and/or improved by an appropriate hair care product.
Materials and Methods
i) The measuring device: The TL 701 Handy Rub Tester (3D motion friction measurement equipment,
HRT) developed by Trinity Lab, Inc. (Tokyo, Japan) (9) has a specific urethane-based sensor tip (photo 1)
of about 1 cm2 area that internally comprises a highly sensitive movement sensor with a 2-axis load cell
and an acceleration sensor to calibrate the outputs of the load cell by millisecond units. Measurement
quantities include the normal force (Fn) and the tangential force (Ft) as illustrated by scheme 1. The
coefficient of friction (COF) can therefore be expressed as the ratio Ft/Fn. The measurement is recorded as
two load cells data (unit: N), Coefficient of Friction (COF), and acceleration sensor data (X-Y-Z axis, unit:
G) in milliseconds. In short, the probe may be viewed as a highly sensitive haptic sensor.
Scheme 1: Principle of frictional force evaluation (Ft/Fn) and Photos 1 (Left and Right): The HRT device
and its recording sensor tip (right)
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ii) Protocol: 9 standardized hair swatches of virgin/untreated hairs of Japanese origin (length 27 cm, weight
1.0g) supplied by International Hair Importers & Products, Inc. (New York, USA) were all initially washed
with a commercialized bland shampoo, rinsed with tap water (35 °C), and dried under ambient dark
conditions. 3 swatches were left untreated and 6 were slightly bleached using a commercialized slight
bleaching product (Persulfate-based) for 30 minutes at 35 °C. Once rinsed and dried off, 3 swatches from
these 6 bleached samples were again submitted to the same procedure, referred to here as “medium
bleached” swatches. Once rinsed and dried off, all swatches were further applied and fixed onto a
horizontal plastic plate. The HRT probe was then manually displaced along 20 cm of the surface of hair
swatches for 4 seconds. The recorded signal is therefore an average value of the surface status along the 20
cm distance since the latter slightly varies along the hair fibers (4). The normal force (Fn) applied onto the
swatch was set to a 250-350 gf range, in both directions: root to tip (R-T) and tip to root (T-R). Dedicated
software automatically stops the measurement when the applied normal force is between 250 gf and 350 gf.
iii) Transforming raw data into sounds: The recorded/stored signals were further transformed to a sound
through an algorithm called “Soniphy®” (El Produce Inc., Ide Sound Institute, Tokyo, Japan) (10). As the
first step, the hair friction raw data is filtered (e.g. high/ low pass filter) by removing the unnecessary data
and setting the threshold. Then, the filtered COF data is converted into a) music and b) signals (Figure 1).
Figure 1: Raw data conversion into sound
a. Musical Conversion: First, the maximum and minimum COF values are detected based on the natural
and medium bleached hair surface status analyzed here. Then, 88 music notes are mapped to the COF
range. A melody is created based on the filtered COF data within a chosen music range. Second, the
suitable pitch range is adapted for people to recognize the hair character. The time range is also selected, by
narrowing or expanding time, to emphasize the hair character (Scheme 2). Finally, the melody is arranged
(e.g. selection of music scale and tone, addition of back sound music).
Scheme 2: Application of COF range to 88 music notes and selection of the best pitch range by
“Soniphy®”
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b. Signal Conversion: The hair friction raw data is converted into sine waves using the “Soniphy ®”
algorithm with 1/million Hz resolution in the audible range (20Hz to 20KHz) (Scheme 3). The signal data
are analyzed mathematically. In this study, the data are analyzed with Fourier transformation to create the
frequency spectrogram. Then, the music score from the “Musical Conversion” was also analyzed to
observe the melody pattern.
Scheme 3: Illustration of signal conversion within the audible frequency band (20Hz to 20KHz)
The pitch range can be adjusted as needed when dealing within more severe cases of surface alteration.
Results
1) Hair Friction raw data.
According to the previously described protocol, the hair surface friction levels of the three groups
of swatches were determined (3 passes per swatch) in both directions (R-T, T-R). Figure 2 shows that the
COF significantly increases with bleaching intensity in the R-T direction (0.4 to 0.54). The T-R direction
logically leads to higher COF values, although significantly less in medium bleached swatches, as
compared to untreated swatches (1.01 to 0.9). Such a result likely reflects the fact that, in medium
bleached swatches, many cuticle scales have been eroded at the tip region, making this part “smoother”
than the root region.
Figure 2: Illustration of the different COF (mean ± SEM) recorded on swatches, according to hair surface
damage level, by moving the HRT probe 1) root to tip or 2) tip to root.
2) Conversion of the COF raw data into sound
This is, to our knowledge, the first attempt to use music theory to illustrate or reflect hair surface condition
through a combination of instrumental data and the “Soniphy®” software.
a. Music Conversion: The COF raw data can thus be converted to a given melody simultaneously with the
measurement by using the new algorithm. In this study, the melody was created with four octave pitches
and harp tones. The acceleration sensor conversion melody was also added as the back sound music (NB: to
be heard during the oral conference).
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b. Signal Conversion: The hair friction data of all hair surface status levels (R-T direction) was converted
to sine waves with 1/million Hz resolution, and the preliminary result is shown as a spectrogram, obtained
through Fourier transformation with the whole pitch range from 27.5Hz to 2489.0 Hz (Figure 3).
Figure 3: Results of conversion of the friction data of all hair surface status levels (R-T direction) into the
spectrogram.
Additionally, the hair friction data of all hair surface status levels (T-R direction) is also converted to music
and signals. The melody was shown as a musical score using general music transformation software to see
the hair rhythm from the melody pattern. To see it easily as a score, it was toned down two octaves and the
time base was expanded (4 sec to 28 sec). The spectrogram from signal conversion was also shown to find
the corresponding musical score. The time base of the spectrogram was also expanded (4 sec to 120 sec).
As a result, we found a unique constant melody pattern for each hair condition. That is, individual melody
patterns were shown by musical analysis (Figure 4).
Figure 4: Results of musical analysis on the music score and comparison to the spectrogram
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Discussion
Consumers of cosmetic products evaluate their performance through visual, tactile and/or
olfactory cues. All of these sensory inputs contribute at different stages to drive overall appreciation
according to specific consumer needs. The sound approach reverses this concept by using sound to provide
the consumer an additional sensorial experience. The alteration of the hair surface induced by bleaching(s)
leads to a higher average friction value corresponding to degraded hair surfaces, in agreement with
previous works (3-5). In this study, natural/untreated hair show an average COF of 0.40 that is translated
into a pitch of 568Hz, while a medium altered hair surface presents a COF of 0.55 translated into a pitch of
1,760Hz, i.e. sharper. As the application of hair care products is well known to decrease the overall friction
value of an altered hair surface (11), the perceived efficacy of treatments that smooth the hair surface could
then be quantified by raw data and/or translated into a personalized consumer “melody”. For the sake of
scientific rigor, we initially chose a well-documented frictional effect on the hair surface. In short, we
believe that the conversion of an electronic signal into a given sound should only be based on a meaningful
physical signal. This procedure creates a new experience by stimulating the auditory senses in addition to
the usual tactile and visual feedback experienced by the consumers, experts, or hair salon professionals.
Such approach may not be limited to hair fibers. It could be extended to the study of the effects of some
skin care procedures, products, or to epidemiological studies. Furthermore, such conversion thus affords a
wide range of possible sensorial applications (sound, music, and light) as stimuli toward consumers or hair
professionals. These preliminary experiments likely pave a new way in the assessment of cosmetic product
efficacy and claim substantiation by adding another dimension in the overall perception of benefits brought
by a cosmetic regimen.
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