Open Journal of Acoust i c s , 2011, 1, 41-54
doi:10.4236/oja.2011.12006 Published Online September 2011 (
Copyright © 2011 SciRes. OJA
Some Aspects of Analysis of Dolphins’ Acoustical Signals
Vyacheslav Ryabov
Karadag Natural Reserve of NAS of Ukraine, Kurortnoe, Feodosia, Ukraine
Received August 3, 2011; revised August 19, 2011; accepted August 22, 2011
Dolphins produce various types of sounds in a wide range of frequencies. Characteristics of some sounds till
now have not been correctly registered, that influenced on interpretation of their functions. Studying of the
characteristics and functions of dolphins’ acoustical signals is the purpose of the present work. In this work
the acoustical signals of two dolphins (Tursiops truncatus) were registered by two-channel system in the
frequencies band up to 200 kHz at quasi-stationary position of the dolphins. The dolphins along with whis-
tles are producing the packs of coherent and non-coherent broadband pulses. The waveform and spectrum of
coherent pulses was invariable within a pack, but considerably varies from a pack to a pack. The waveform
of each non-coherent pulse vary from a pulse to a pulse in each pack, therefore their spectrum also vary from
a pulse to a pulse and have many extremums in the band of 6 - 200 kHz. It is very likely that the non-coher-
ent pulses play a part of phonemes of a dolphin spoken language and the probing signals of dolphin’s non-
coherent sonar. The use possibility of the signals by dolphins for communication and orientation was con-
sidered, as the signals apparently are bimodal. Results of the work have significance for further studying of
the dolphin’s sonar and spoken language.
Keywords: Dolphins, Hearing, Sonar, Acoustical Signals, Language, Orientation
1. Introduction
Cetaceans are secondary-aquatic mammals which have
completely returned to living in the sea. It is supposed,
that they evolved from primitive ungulates, or it is prob-
able, from carnivores which foraged in coastal waters
until completely adapting to a complete life in the sea,
approximately 50 - 70 million years ago [1-4]. The fossil
records of the early Oligocene shows evidence of diver-
gence between the suborders Odontoceti and Mysticeti.
Till now there are at least 65 recognized species of Odon-
toceti which represent carnivores [5,6].
It is known that Odontoceti undergo a number of func-
tional and morphological modifications in the process of
secondary adaptation to the aquatic habitat. It is tempting
to think that the most vivid modification known as tele-
scoping of a skull [7] was associated, among other rea-
sons, with the development of the own echo-location
system and peripheral part of hearing, while the conver-
gence of the lower-jaw halves at the level of mental fo-
ramens reflects the optimization of aperture and base of
the new external ear [8-11].
In Cetaceans the encephalization hypothetically arise
rapidly and already 25 million years ago they had a brain
weight more than of Homo sapiens. Average weight of a
dolphin brain of 1587 g, it is more convoluted and hav-
ing more surface area per unit of volume than a human
brain [12].
Though experiments with dolphins are conducting
from the middle of the last century, questions about ne-
cessity of such brain as well as about existence possibil-
ity of a highly-developed language and supreme forms of
a consciousness are still discussing.
In the same time there were achieved certain successes
in the studying of dolphins’ acoustical signals. The tonal
frequency-modulated whistles and packets of short
broadband acoustical pulses or the pulse burst are
thought to be the sounds primarily playing a role in so-
cial interaction of dolphins [13-21]. However, these
acoustical signals mostly were studied in a frequencies
band up to 20 kHz, therefore, the authors practically in
all these works, discussed them as signals with the ma-
jority of energy on frequencies from few hundred to a
few thousand Hz. Recently some of these acoustical sig-
nals are studied in more details in frequencies band up to
130 kHz [22,23]. Authors have shown, that free-ranging
the Hawaiian spinner dolphin (Stenella longirostris) and
the Atlantic spotted dolphin (Stenella frontalis) are pro-
Copyright © 2011 SciRes. OJA
ducing the packs of short broadband pulses (the burst
pulses), on the average approximately 30 and 100 pulses,
with a mean interpulse interval 3.85 ms and 3.19 ms,
respectively. The spectrum maximum and the central
frequency of the pulses for spinner dolphin were on av-
erage 32.3 and 40.1 kHz, respectively, for spotted dol-
phins these were somewhat higher at 40.3 and 44.4 kHz,
respectively. The power spectrum width of these pulses
roughly 20.5 kHz for spinner dolphin and 18.1 kHz for
spotted dolphins. Spectral energy distribution in the
pulses did not depend on position of the pulse in a pack
or an interpulse interval. Only less than 20% of pulses
had peak of energy on frequencies below 20 kHz. On the
average more than 80% of pulses energy was on fre-
quencies above 20 kHz for both species. At the same
time authors have shown, that the waveforms of these
pulses and the dolphin’s sonar clicks could not be read-
ily distinguished from the other. Therefore, click train
were considered as burst pulses if their mean interpulse
interval did not exceed 10 msec. Dolphins produced
these pulses primarily on close distances to each other
up to 3 - 14 m, therefore authors have assumed, that
dolphins use these pulses for exchange of emotional
signals [23].
Thus, the dolphin’s acoustical signals have been reg-
istered mainly incorrectly (inadequate band of frequen-
cies and levels of records that lead to clipping and distor-
tion of a signal’s waveform; random position of a dol-
phin relatively of a hydrophon). Therefore in this work
the acoustical signals of two dolphins (Tursiops truncatus)
were registered by the two-channel system with a wide
dynamic range in the frequencies band up to 200 kHz at
quasi-stationary position of the dolphins. The dolphins
during registration were producing various types of the
signals freely, not suspecting at all, that they are regis-
tered at this time. The two-channel system of registration
has advantage in comparison with a single-channel one
because enables to restore spatial localization of sound
sources and to give the qualitative evaluation of the sig-
nals directivity (as the result of processing the difference
in levels and arrival times of the signal between the
channels). Thanks to this the recorded signals had
matched precisely with each dolphin, as well as all re-
flections of the signals from the edges of pool. Till now
the acoustical signals of dolphins were not registered by
a two-channel system.
The studying of characteristics and functions of the
dolphins’ acoustical signals is the purpose of the study.
Specific tasks consisted in the recordings and subsequent
analysis of the signals produced by two dolphins of one
species by the two-channel recordings system in the pool
conditions, in frequencies band of 0.1 - 220 kHz.
2. Procedure
Experiments were carried out on two adult Black Sea
dolphins (Tursіops truncatus) with nicknames Yasha
(male) and Yana (female), in the indoor pool of 23 × 9 ×
4.5 m of Karadag Natural Reserve of NAS of Ukraine.
The dolphins are in the pool about 20 years and have
normal hearing.
The experimental configuration is shown in Figure
1(a). The experiment was carried out without special
training of the dolphins. The time intervals when the dol-
phins approached near to the gangway (5) and remain on
a water surface, almost without locomotion (Figure 1(b))
were used for recording their acoustical signals. The
signals are recorded by the two-channel recording system.
The matching of the registered signals with the dolphins
as well as and the reflections of the signals from the
edges of pool (the side walls, the bottom, the surface of
water) were performed at the two-channel recording ana-
lyzing. For this purpose the signal arrival times differ-
ence and the levels difference of the given signal on the
hydrophones of channels I and II as well as and known
distances between the dolphins, the hydrophones and the
edges of pool were taken into consideration.
The distance between the hydrophones (the base 3.5 m)
were chosen such to receive the necessary difference in
levels and arrival times of each signal on the hydro-
phones, and to arrange them in the dolphin’s far acoustic
field (approximately > 1.5 m). At the same time, the
hydrophones were placed 1 m below the water surface in
order to reduce the probability of signals shielding by the
other dolphin in direction of the hydrophone distant to
the dolphin producing sounds (Figure 1(a)). Besides, the
hydrophones were located so that (2) was placed near to
the pool sidewall whereas another one (1) further of the
sidewall for signals reverberation evaluation in the pool.
The recordings were obtained by using the spherical
hydrophones (1 and 2) with diameter of 14 mm and cali-
brated sensitivity 203.5 dB and 206 dB relative to 1
V/µPa, or 66.5 and 50 µV/Pa, respectively. The hydro-
phones’ frequency characteristics have irregularity of
±3dB up to frequencies of 160 kHz and ±10 dB up to
frequencies of 220 kHz. Each recording channel consisted
of the hydrophone, the 0.1 kHz high-pass filter, the 40dB
voltage amplifier and the one channel of the 14 bit ana-
log-digital converter (USB-3000). The digitized signals
of the dolphins during recording were continuously trans-
ferring from the analog-digital converter to the hard disk
of notebook via interface USB 2.0. The analog- digital
converter has dynamic range of 81 dB and sampling fre-
quency of 1 MHz for each channel. The frequency char-
acteristic of the analog-digital converter at the given
sampling frequency was flat up to 160 kHz and smoothly
Copyright © 2011 SciRes. OJA
Figure 1. The experimental configuration. (a) 1, 2 are the hydrophones of channels I and II, respectively. The distance be-
tween hydrophones is 3.5 m at the depth of 1 m. 3, 4 are the dolphins Yana and Yasha, respectively. The distance between
dolphins is about 1 m. 5 is the gangway located 0.1 m above water surface. 6, 7 and 8 are the long wall, short wall and bottom
of the pool, respectively. The distance between the hydrophone 2 and sidewall 6 is 0.45 m. The distance from hydrophones to
the wall 7 is 3 m. The water level is 4 m. (b) The quasi-stationary position of the dolphins during the recording.
fell down to 3 dB on frequency 200 kHz for each chan-
nel. The programs packages of PowerGraph 3.3.8 and
Adobe Audition 2.0 were using for recording and analyz-
ing acoustical signals of the dolphins. The 4096-point
FFT with Hamming windowing function or 1024-point
FFT were used for the signals spectrums computing,
Figure 2 and Figures 3-5, respectively. A lot of acousti-
cal signals produced by the dolphins freely at will were
recorded. The most typical recording (Figure 2) was
chosen for the analysis and discussion. The dolphins were
in quasi-stationary position (Figure 1(b)) in relation to
the hydrophones and each other during the recording
(Figure 2), approximately 34 sec. No other mammals
were in the pool during the signals recording.
3. Results
The time dependence of all sounds produced by the dol-
phins during of 34 sec of the recording and the sonogram
of area with whistles from 3th to 14th sec are given in
Figure 2. One can see that the dolphins produced the
packs of pulses with the time intervals between the packs
(789 - 4000 msec) more than the interpulse intervals (Ta-
ble 1). The packs sequence in Figure 2 is designated by
the numerals (1 - 10). Duration of the pulses in the packs
vary from 80 µsec up to 600 µsec. The waveform of each
pulse is complex (Figure 3) and varies from the pulse to
the pulse in each pack. Therefore, the spectrum of each
pulse as well varies from the pulse to the pulse (Figure
3(a)). In this connection, I have named their as the
non-coherent pulses. The spectrum of the non-coherent
pulses covered approximately all hearing range of a dol-
phin, from 6 - 15 up to 160 - 200 kHz and had many
maximums and minima. However, considering that hear-
ing thresholds of a dolphin steeply increase from fre-
quencies above 135 kHz the signals sonograms in Fig-
ures 3 and 5 are presented only up to 160 kHz. The sound
pressure levels (SPL) of the non-coherent pulses vary
from 15 up to 330 Pa (Figure 2). The number of pulses
in the packs varies from 4 up to 27 pulses, but more often
the packs have from 6 up to 8 pulses with the interpulse
interval from 19 msec up to 300 msec (Table 1). The
arrows near numerals (Figure 2(a)) specify the direction
of pulses transfer, from Yasha to Yana or on the con-
Except the non-coherent pulses there were recorded
also the packs of pulses with the waveform and spectrum
that are invariable within each the pack but significantly
vary from a pack to a pack (Figures 2-4). In this connec-
tion I named them as the coherent pulses. The SPL of the
coherent pulses not exceed of 3 - 5 Pa what are about
two orders lower of the SPL of the non-coherent pulses
(Figure 3). In the Figure 2 these pulses are barely per-
ceptible, thus the producer of the coherent pulses is des-
ignated by the conventional sign nn (where n is the serial
number of the pack) in the pack localization place, re-
spectively. In the Figures 3 and 4 these pulses are shown
in more convenient scale. The waveforms of coherent
Copyright © 2011 SciRes. OJA
Figure 2. The time dependence of the dolphins’ acoustical signals (a). The sonogram of area with whistles (b). Along X-axis
are the signals locations on the time axis. Along Y-axis are SPL in dBs relatively 350 Pa and frequencies in kHz, respectively.
The numerals (1 - 10) are the packs sequence. The arrows near the numeral specify the message transfer direction. wn and nn
are localization nth whistles and nth packs of the coherent pulses, respectively. I and II are the channels numbers, respec-
pulses are complex, the pulses duration was about 350 -
650 µsec (Figures 3(b) and 4). The spectrum of coherent
pulses covered the frequencies band from 7 - 10 up to 22
- 100 kHz and had many maximums and minimums.
There were the packs of the relatively narrow-band and
broadband pulses. The interpulse interval in packs of
coherent pulses always varies, as a rule gradually de-
creasing from the beginning to the end of a pack and is
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Table 1. The characteristics of the non-coherent pulses’ packs.
pack number 1 2 3 4 5 6 7 8 9 10
pulses numbers
in pack 23 8 4 6 7 8 6 27 14 19
interval (msec) 90 - 266 80 - 230 180 - 240160 - 21289 - 13687 - 18195 - 17019 - 126 68 - 112 31 - 138
pack duration
(msec) 3850 860 580 770 620 890 620 1250 1100 1120
122 non-coherent pulses in all
Figure 3. The non-coherent (a) and coherent (b) pulses of the dolphins in the time (above) and frequency (underneath) do-
main. Along X-axis are signals locations on the time axis of Figure 2. Along Y-axis are SPL in dBs relatively 350 Pa, the rela-
tive amplitudes of sonogram in dBs and frequencies in kHz, respectively. The time scale for the pulse produced on 32.81th sec
is 200 µsec/div, and 100 µsec/div for the rest.
seldom on the contrary (Figure 4(a), Table 2). The rela-
tive variation of interpulse interval was within of 1.1 -
5.6 and not depended from duration of a pack. The packs
contain from 20 up to 611 pulses with the interpulse in-
terval within of 1 - 41msec (Table 2).
The dolphins produced five frequency-modulated whis-
tles with harmonics up to 100 kHz (Figure 2(b)). The
whistles producer is designated by the conventional sign
wn (where n is the serial number of whistle) in the whis-
tles localization places, respectively. Fundamental fre-
quency of the whistles (Figure 2(b)) vary in the band of
821kHz, 8 - 16 kHz, 8 - 22 kHz, 3 - 16 kHz and 2.8 - 28
kHz, and the number of harmonics on the hydrophone
placed near to whistling dolphin were of 1, 2, 1, 4 and
about 16, from first to fifth whistle, respectively. On the
distant hydrophone from whistling dolphin the harmon-
ics were absent at first three whistles, at fourth whistle
their quantity was the same, at the fifth whistle were
about 7 harmonics. On account of relatively low SPL of
the whistles and coherent pulses their reflections from
the sidewalls and bottom of the pool, apparently, were
masked by noise and are imperceptible.
At the same time the reflections of the non-coherent
pulses are well visible both in the time and frequency
domain (Figure 5). On account of the dolphins’ quasi-
stationary position the reflections locating of the each
non-coherent pulse from pool edges approximately are
identical and for the example is given in Figure 5 for the
pulse that Yana produced on 10.88th sec.
4. Discussion
Dolphins specially were not trained to produce acoustical
signals in this experiment. Besides, their position on a
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Figure 4. Example of the time dependence of interpulse interval in the pack of coherent pulses (a) that Yana produced from
16.8th up to 17.6th sec (n4, Figure 2) and a magnification of the area from 17.185th up to 17.23th sec represented in the time
(c) and frequency (d) domain. The single pulse (b) at the expanded time scale of 200 µsec/div. Along X-axis are pulses location
on the time axis of Figure 2(a). Along Y-axis are SPL in dBs relatively 350 Pa and frequencies in kHz, respectively. The rela-
tive amplitudes scale of sonogram is the same as in Figure 3.
Table 2. The characteristics of the coherent pulses’ packs. In the row “interpulse interval” the first value is the interpulse
interval in the pack beginning, the second value in the end.
pack number 1 2 3 4 5 6 7 8 9 10
numbers in pack 24 611 20 86 73 56 119 72 202 104
interpulse interval
(msec) 8.5 - 62 - 1.8 1 - 2.5 28 - 5 13 - 519 - 6.541 - 13.515 - 4 9.5 - 3.8 29.5 - 5.7
relative variation of
interpulse interval 1.4 1.1 2.5 5.6 2.6 2.9 3 3.7 2.5 5.2
pack duration (msec) 300 1100 40 850 820 505 670 410 758 822
1465 coherent pulses in all
water surface almost without locomotion (Figure 1(b))
more likely speaks to an outside observer that they dozed.
However, when the two-channel recording system was
turned on it was discovered that the dolphins at this time
carry on the lively conversation using the main arsenal of
signals communication (Figure 2). This means that after
20-years of theirs staying in the pool the dolphins still
have what to tell to each other!
The dolphins did not produce outgoing pulses (clicks)
of the sonar with rostral directivity [24] during this re-
cording (Figure 2), probably, in it was not necessities;
therefore their melons were partially above water.
Though, the standard stereotype acoustical clicks with
duration approximately 25 µsec and the spectrum maxi-
mum near of 115 kHz were recorded during other re-
cording when the dolphins were under water. It is neces-
sary to note, that SPLs both the non-coherent and coher-
ent pulses were by one-two orders less of the sonar’s
clicks levels. Besides, each type of the pulses mostly had
characteristic waveforms.
All recorded pulses (Figures 2-5) apparently are the
acoustical signals that widely considered as the dolphins’
social signals [13-21]. However, in these works the
packs of pulses were studied in the frequency band up to
Copyright © 2011 SciRes. OJA
Figure 5. The non-coherent pulse that Yana produced on 10.88-th sec (Figure 2) and the pulse reflections in the time (a) and
frequency (b) domain. 1 is the non-coherent pulse. 2 is the echo from wall (6, Figure 1). 3 is the echo from dolphin Yasha. 4 is
the echo from wall (7). 5 is the echo from pool bottom (8). 6 is the double echo: the bottom of pool—the surface of water. 7 is
the echo from wall opposite to wall (6). Along X-axis is the time in msec. Along Y-axis are SPL in dBs relatively 277 Pa, and
frequencies in kHz, respectively. The relative amplitudes scale of sonogram is the same as on Figure 3.
20 kHz, therefore it is difficult to compare the obtained
results (Figures 2-5) with the literature data. In the same
time the recorded pulses have too low energy levels on
frequencies of human hearing and at playing back the
record as a result there are only weakly audible the
pulses-repetition frequencies. Therefore, to classify the
Copyright © 2011 SciRes. OJA
pulses aurally as: “quack”, “squeak”, “squawks”, “bark”,
“squeal”, etc. [16] it turns out practically impossible. In
this connection, apparently, it is necessary to agree with
the opinion stated in the work [22], and to reconsider
classification of dolphins’ signals in view of their physi-
cal characteristics. Therefore in the present work the re-
corded pulses are described mostly from the point of
view of their physical characteristics.
In total the dolphins had produced 122 the non-
coherent pulses in 10 packs, 1465 the coherent pulses in
10 packs and 5 the whistles, for 34 sec! All recorded
whistles (Figure 2) contained harmonics quantity more
on the hydrophone nearest to whistled dolphin. In gen-
eral, the types of fundamental frequency contours of
whistles and the harmonics quantity are typical for these
animals [25-29].
The characteristics of the coherent pulses (Figures 3
and 4, Table 2) are practically completely coincide with
the burst pulses registered in free-ranging the Hawaiian
spinner dolphin (Stenella longirostris) and the Atlantic
spotted dolphin (Stenella frontalis) [22,23]. Moreover,
the dolphins Yana and Yasha gradually controlled the
interpulse interval value in each pack (Figure 4 and Ta-
ble 2), and in the different degree. The relative changes
of the interpulse interval were from 1.1 up to 5.6. The
interpulse intervals in the packs of coherent pulses al-
ways vary, as a rule, gradually decreasing from the be-
ginning to the end of a pack and are rare on the contrary.
In general, the value control of interpulse interval also it
is possible to consider as control of the phase of each
subsequent pulse in the pack.
The dolphins in each case used the necessary quantity
of pulses (from 20 up to 611) with the necessary inter-
pulse interval (from 41 up to 1 msec) (Table 2). Besides,
the dolphins used pulses of the necessary waveform and
spectrum in each pack. Spectrum of the coherent pulses
of Yana and Yasha also as and of Hawaiian (Stenella
longirostris) and Atlantic (Stenella frontalis) dolphins,
had many maximums and minima and covered the fre-
quencies band up to 100 kHz. The spectral maximums
and minima in each pack as well as and the pulses
waveform did not vary in the pack but ones significantly
vary from the pack to the pack (Figures 3 and 4). Major
energy of the coherent pulses is concentrated on fre-
quencies above 7 - 10 kHz, and there were packs of rela-
tively narrow-band and broadband pulses as in work [22].
Hence, Black Sea dolphins (Tursiops truncatus) pro-
duced the packs of coherent pulses (Figures 2-4) just
like and the Hawaiian and Atlantic dolphins [22,23].
The locating of all dolphins signals in the time domain
has character of an exchange of three types of signals,
Figure 2(a). The signals of each type each dolphin has
produced in turn, without the overlapping in time. For
the whistles produced by Yana (Figure 2, w1 - w3) Yasha
did answer with the whistle (w4), after that the whistle of
Yana (w5) follows again. In the same way, without over-
lapping in time, the dolphins do exchange packs of the
coherent pulses (Figure 2, n1 - n10). In total, Yana pro-
duced 7 packs of the coherent pulses (548 pulses) and
Yasha 3 packs of the coherent pulses (917 pulses).
The dolphins exchange packs of the non-coherent
pulses in a more complicated manner (Figure 2). There
is obvious levels distinction of each pulse between chan-
nels I and II. Yana is located (Yasha is located) during
all record nearer to hydrophone of channel I (II), there-
fore on channel I (II) all pulses which she (he) produces
have level higher. The packs of non-coherent pulses (2, 3,
4, and 6, Figure 2) have less appreciable distinctions of
the levels between channels I and II, therefore the pro-
ducers of these pulses have been identified in view of the
difference in the pulses arrival time on the hydrophones.
In the pack (2) both dolphins produced pulses almost
simultaneously and therefore, it is possible to assume,
that they not understood each other, therefore Yasha has
conceded and has allowed the lady to express oneself
(packs of 3 - 5). In the pack (6) again, both dolphins al-
most simultaneously produced pulses, and though Yasha
gradually increased their level, from the pulse to the
pulse, Yana, apparently, again not listened him, then he
loudly shout (last pulse in the pack 6). Then, after the
short pause Yasha produced the packs of pulses (7 - 10)
already up to the end of the record, having lowered the
loudness of voice (the packs of 8 - 10).
The signals of different type could be produced by
each dolphin simultaneously (Figure 2). So, Yana si-
multaneously produced as the coherent pulses and whis-
tles from 5.4th to 5.8th sec and from 11.9th to 11.95th
sec, so and the non-coherent pulses and the coherent
pulses from 26.26th to 27th sec. Yasha produced simul-
taneously the non-coherent pulses, coherent pulses and
whistles from 7.6th to 9th sec. These facts testify that
each type of the signals was produced independently by
the appropriate organ of dolphins. Hence, in view of the
sonar clicks of a dolphin [24], apparently, in a dolphin
should be at least four the organs that independently
produce four types of signals.
Inasmuch as in the pool there were no other animals
and the dolphins nobody forced to produce any sounds, it
is possible to believe, that dolphins produced all these
sounds or for communication with each other, or for ori-
entation in the pool in spite of daylight (i.e. to feel the
moving concerning each other, the walls and bottom of
pool; to monitor ambient environment for distance more
than water transparency). In what degree each type of the
recorded signals can be used by the dolphins for the
communications and orientation?
Copyright © 2011 SciRes. OJA
The non-coherent pulses produced by the dolphins
differ from each other by the waveform in time domain
and by the set of spectral components in frequency do-
main (Figure 3). In this connection it is possible to as-
sume, that each non-coherent pulse represents the pho-
neme of the speech of a dolphin spoken language and
every pack of the non-coherent pulses is a word, then
sequence of the packs of the non-coherent pulses is the
sentence. For the best understanding, we shall compare
speech of a dolphin spoken language with speech of a
human spoken language. In dolphins the phonemes spec-
trum covers almost all frequencies band of a hearing,
from 6 - 15 kHz up to 160 kHz. Frequencies approxi-
mately below 6 - 15 kHz (Figure 2(b)), apparently, are
excluded from a dolphin speech for increasing a speech
noise-immunity, because for the frequencies below ap-
proximately 10 kHz both a dolphin’s hearing thresholds
and a level of environmental noise significantly increase.
Phonemes spectrum of a human speech also covers al-
most all frequencies band of a human hearing, but ap-
proximately 0.3 4 kHz is necessary and sufficient for
speech intelligibility; however this frequencies band is
located primarily beyond coverage of a dolphin speech.
The duration of dolphins phonemes are relatively very
short, 80 - 600 µsec, that on 2 - 3 orders shorter than
duration of a human phonemes. In addition, between
dolphins phonemes there are relatively long-duration
interpulse intervals (the characteristic value nearby of
150 msec). This interval can widely vary and, apparently,
is necessary for phonemes immunity from reverberations.
The phonemes of a human spoken language also consist
of spectral components, but as opposed to a dolphin a
human is producing phonemes of one word inseparably,
as a solid word. In this connection duration of a dolphin
word and a human word can be approximately identical
at identical quantity of phonemes. Probably, in the
free-ranging dolphins the interpulse interval will be con-
siderably less in this case words duration will decrease.
Certainly, it is hardly likely, but every the non-coher-
ent pulse of a dolphin may be represents the word and a
pack of pulses represents the sentence, but at present this
is inessential as the answer to this question will be given
by the further researches.
It is possible to estimate in what degree the spoken
language of a dolphin possesses the Hockett’s 13 design
features of human language [30]. The design features we
will consider in the order, like they were introduced by
1th - 6th of the design features, obviously, are inherent
for the dolphin and, apparently, do not demand special
discussion. It is more interesting to consider from the 7th
to 13th features because ones in a significant extent are
determined by an intellect and level of an animal’s con-
7) Semanticity. It were shown experimentally [31,32]
that dolphins understood novel instructions conveyed
within artificial gestural or acoustic language systems
using “sentences” as long as five words whose interpre-
tation required processing of both the semantic and syn-
tactic features of the languages. That maybe present in-
direct confirmation that and in the spoken language of a
dolphin a specific signal can be matched with a specific
8) Arbitrariness. Concept learning was demonstrated
within artificial gestural or acoustic language systems
within several paradigms, including discrimination
learning sets and matching-to sample [33]. This is indi-
rect confirmation that and in the spoken language of a
dolphin there is no limitation to what can be communi-
cated about and there is no specific or necessary connec-
tion between the sounds used and the message being
9) Discreteness. In the spoken language of a dolphin
the phonemes discreteness (Figure 3) is determined by
the different locating on frequency and level of the
maximums and minima of spectral components. It is easy
to notice, that these distinctions more than differential
thresholds of a dolphins’ hearing on frequency—about
0.2% - 0.8% in a frequencies band of 10 - 130 kHz
[34-36] and on intensity—about 10% [37,38].
10) Displacement. It was shown that the dolphin un-
derstood gestural instructions within artificial gestural
language system as reliably when conveyed through
television images of trainers as when conveyed by live
trainers. The words of that language were understood
referentially, including an ability to report whether a ref-
erenced object was present or absent in the dolphin’s
tank [33,39]. It attested that a dolphin have ability to
refer to things in space and time and communicate about
things that are currently not present and indirectly testi-
fies that a dolphin have the high level of consciousness
and may have the highly-developed language.
11) Productivity. It is possible to estimate approxi-
mately what quantity of words can to be created from
various combinations of separate spectral components in
the spoken language of a dolphin. If at analysis of the
pulse spectrum (i.e. the phonemes) the dolphin uses the
mechanism of critical bands with about 10% width from
the central frequency of the hearing filter [40-43] then in
the frequencies band of 10 - 130 kHz about 15 critical
band are located. We shall assume, each phoneme con-
sists of 10 spectral components (10 spectral strips of
Figure 3). Then the quantity of different phonemes can
be equal to the number of permutation of 10 out of 15,
without recurrences that give nearby 3*103. This is ob-
viously excessive. If the dolphin spoken language uses
Copyright © 2011 SciRes. OJA
by analogy to human spoken language even 30 different
phonemes from them it will be possible to create quantity
of words comparable to productivity of a human lan-
guage for which, as it is known, this value is defined by
number with 26 zero. In what degree the spoken lan-
guage of a dolphin is opened, it will be possible to tell,
apparently, only at further studying of the language.
12) Traditional transmission. Nongenetic transmission
of social behavior across generations was observed for
Cetaceans [44,45], it suggest that, these large-brained,
slow-developing, and socially complex species [46] have
evolved powerful social-learning mechanisms. Some po-
tential scenarios and mechanisms observed for a group of
free-ranging Atlantic spotted dolphins (Stenella frontalis),
including implications of vertical, horizontal, and oblique
directions of transmission of social information during
various behavioral contexts are described [47]. Teaching,
then, may be an important way in which aspects of ceta-
cean social learning and possibly culture are transmitted
from one generation to the next [48]. These outcomes
suggests while certain aspects of language may be innate,
dolphins maybe acquire words and their native language
from conspecifics.
13) Duality of patterning. On the basis that the dol-
phins’ spoken language consist from phonemes it is pos-
sible to assume that and dolphins have ability to recom-
bine a finite set of phonemes to create an infinite number
of words, which in turn can be combined to make an
unlimited number of different sentences.
Thus, the spoken language of the dolphins, expressly
or by implication, conforms to all the design features of a
human language, and it is possible to consider as the
highly-developed language. In favor of this as well indi-
cate the facts that dolphins possess large and highly de-
veloped brain already more than twenty million years
But, unfortunately, the frequency-time characteristics
of a dolphin speech are localized outside limits of a hu-
man hearing, therefore a dolphin speech exist beyond
reach of a human hearing. In contrast to it the frequency-
time characteristics of a human speech are localized
within the area of a dolphin hearing, nevertheless as a
result of significant reflection of sound energy on
air-water interface, a dolphin hear an attenuated human
speech. In this connection, for an establishing of mutual
relations with these intellectual mammals a human
should take the first step should create a device capable
to overcome the physical restrictions for use of both
languages. It should like to think, that dolphins will tell
the last word at decoding the languages because they
seemingly can possesses even higher forms of con-
sciousness than human.
As it follows from the record (Figures 2 and 5) the
echo-signals of the non-coherent pulses both from side-
walls and pool bottom and even from dolphin Yasha
have the high levels. In the other words the echo-signals
levels from rostral, lateral and ventral directions of the
dolphins are approximately identical. Hence, these pulses
have no directivity and play a role of both the dolphin
speech phonemes and the probing pulses of the non-co-
herent dolphin sonar which necessary for near orientation
in coastal conditions of shallow water and rocks, and
also for orientation among floating relatives. Meanwhile,
rather small phonemes duration and rather wide interval
between phonemes define high time resolution and
anti-reverberation immunity of the dolphin speech. The
mean values of interpulse interval in the packs of the
non-coherent pulses on the record (Figure 2) were about
150 msec, that give the sonar range indirect assessment
at least about 112 m in view of the two-way of a sound
up to the target. The length of our pool is 23 m, so the
dolphin produced every pulse on the average after the
fivefold echo along the pool from previous.
Absence of the directivity non-coherent pulses is caused
due to natural necessity in broadcast transmission both
the phonemes and probing pulses. Whereas the direc-
tional reception both the echo-signals and dolphin speech
from all directions around of a dolphin can be performed
by a new external ear [8-11] with the localization accu-
racy of 1˚ - 3˚ [49-51].
Hence, the non-coherent pulses are of great impor-
tance both for dolphins’ communication as the speech,
and for orientation as the probing pulses of non-coherent
sonar, i.e. the pulses are bimodal.
What significance may have the whistles and coherent
pulses for communications and orientation of dolphins?
The major energy of whistles coincides with frequencies
band of human hearing, therefore a lot of works is de-
voted to studying of these signals and has been stated
more hypotheses, in comparison with other types of dol-
phins acoustical signals. Large repertoires of the con-
text-specific whistles that vary according to situation or
activity were described and discussed [25,26,52]. In ad-
dition the whistles can presumably be used by dolphins
as the signature-whistle identifying each dolphin among
the others as individually distinctive according to the
whistle contour [27]. Besides, the whistles can play an
important role in maintaining contact between dispersed
conspecifics [28], and also for definition of a direction of
movement of a whistling dolphin [24,53]. The calculated
range for dolphins’ communication by whistles corre-
sponds approximately of 10.5 km, for whistles with
highest (167 dB re. 1 µPa) source level [29].
It is interesting that whistling obviously is not used in
the human speech. At the same time, even not realize it,
the human easily can whistle from surprise, can whistle
Copyright © 2011 SciRes. OJA
when good mood, or to whistle loud from far away in
order that to attract attention. The whistle can be trans-
mitted on farther distance than a speech because one has a
lot of energy in the narrow frequencies band. Our dol-
phins, Yana and Yasha apparently know this because they
lift up the heads out from water and can whistle in air,
specially, in order that to draw attention of a human. Thus
they emit very loud whistle with the lowest fundamental
frequency (2.8 kHz, practically without frequency modu-
lation, Figure 2, second part of the whistle w5) which are
audible in the most remote corners of our dolphinarium.
However by analogy with the non-coherent pulses it is
possible to assume, that dolphins can use whistles not
only as communication signals but also for orientation.
From the point of view of physical acoustics the whistles
can be used in the FM-Doppler sonar. In engineering
applications such sonar is used for detecting moving tar-
gets or for measuring the relative radial velocity of target
and for range measurement. The Doppler frequency shift
fD depend on the carrier wavelength λ and the relative
radial velocity (or range rate) between the sonar and the
target Vr, as: fD = 2Vr/λ, where λ = c/f is carrier wave-
length, с is the sound velocity in water, f is the carrier
frequency. Hence, with increase of carrier frequency (of
fundamental frequency of a dolphin whistling) the sonar
wavelength will decrease and so the Doppler frequency
shift will increase that will increase the sensitivity of the
sonar. Meanwhile, the frequencies of whistles harmonics
increase proportionally to the number of harmonic. If
dolphins do analyzing the echo of whistles harmonics,
then thereby they increases sensitivity of sonar propor-
tionally to the number of harmonic. That in some degree
explains availability of plenty harmonics in dolphins
whistles and confirms possibility the harmonics using by
Doppler sonar of dolphins. The maximum sensitivity of
Doppler sonar can be necessary to dolphins on small dis-
tances when it is important the detection of small relative
radial velocities and small relative movings which the
sonar cannot perceive on the fundamental.
Besides it is known, that in engineering applications
the sonar with pulse compression uses a long tonal pulse
with linear or nonlinear frequency modulation similar to
the contours of fundamental frequency of a dolphin whis-
tles. If a FM pulse of this sonar has a spectrum width B,
and the returned echo is processed by the matched filter
with a pulse compression then the pulse response dura-
tion will be approximately 1/В and will not depend on
the duration of the probing pulse. The more a spectrum
width of a pulse, the less a filter reaction duration of the
receiver and in the result it is enhance the range resolu-
tion of sonar. In other words, such sonar receives an echo
with energy as from a long pulse, but with the range
resolution as from a short pulse. Therefore when the du-
ration of whistle will increase then whistle energy will
increase proportionally and the dolphin can receive echo-
signals of conspecifics from greater ranges and with the
higher range resolution. It is interesting to note, that at
maintenance of contact between the separate dispersed
conspecifics, dolphins, apparently, can feel each other
and actively by means of the FM-Doppler sonar (when a
dolphin is whistling and analyzing echo of each conspeci-
fic) and passively (just analyzing the whistling of each
conspecific), in this case the maximum range for ex-
changes of whistles in dolphins can reach up to 10.5 km
[29]. Hence, whistles also as well as and the non-coher-
ent pulses, apparently are bimodal, and ones can be used
by dolphins, at the limited information exchange [24-
29,52,53] as communication signals and for orientation
as a probing signal of the FM-Doppler sonar with a pulse
Dolphins produce the coherent pulses primarily on
close distances to each other up to 3 - 14 m, presumably
for exchange of emotional signals [23], and the charac-
teristics of the coherent pulses suggest that dolphins could
use them as acoustical communication signals. However,
the quantity of the coherent pulses produced by the dol-
phins in one pack up to 611 (Table 2) and even 958 ac-
cording to [22], with gradually varying interval inter-
pulse (or of the phase interpulse), and the coherence of
the pulses in each pack, testifies more likely about utili-
zation of the coherent pulses by the dolphins for orienta-
tion. As well, the spent time for transfer of the same pulse
many times (Figure 4) is obviously not proportionally to
the quantity of information in this pulse that testifies
about the same [54]. But in the literature so far is not
clear with what purpose dolphins use these pulses packs,
thus additional researches are necessary.
However, from the point of view of acoustics the char-
acteristics of the coherent pulses (Figures 3 and 4) com-
pletely conform to the signals of the pulse-Doppler sonar
with high pulse repetition frequency. In engineering ap-
plications such sonar are using packs of coherent pulses
with time intervals between the pulses many times less
than the two-way time of a sound up to the target and
where there is a fixed or deterministic phase relationship
between each successive pulse, i.e. exactly as in the
packs of the dolphins’ coherent pulses (Figure 4, Table
2). Such sonar uses Doppler frequency shift for selection
of the moving target in a severe clatter environment and
radial velocity measuring. It is interesting to note, that
the most studied sonar of a dolphin with a rostral direc-
tivity [24] is using the pulses (the clicks) with stereotype
waveform, i.e. these pulses are coherent. But the pulses
repetition frequency low so, that a time interval between
pulses as a rule is more than two-way time of a sound up
to the target. In engineering applications similar pulses
Copyright © 2011 SciRes. OJA
uses sonar that have been categorized as the moving tar-
gets indication (MTI). The MTI selects the moving target
in a severe clatter environment and measures distance up
to the target. Both pulse-Doppler sonar and the MTI use
the coherent transmission, reception and processing of
echo-signals with the purpose to reject main-beam clutter
and enhance target detection and aid in target discrimina-
tion or classification. Hence, the sonars with the coherent
pulses dolphins in general are used for orientation. But
considering, that all acoustical signals are being proc-
essed by the same hearing analyzer of the dolphin, ap-
parently, these pulses can be used by dolphins both for
transfer of the limited quantity of the information during
social interaction of dolphins and for orientation as the
pulse-Doppler sonar and as the MTI.
5. Conclusions
From findings of this work follows:
1) The echo-location system of dolphins and, appar-
ently, Odontoceti is more complex than it was being
discussed earlier, and it is very likely, the system has at
least four various types of sonars with different types of
the probing signals and with various methods of proc-
essing of the acoustical information.
2) There is a good reason to consider, that dolphins,
and apparently, Odontoceti have the highly-developed
spoken language. These findings confirm the representa-
tion about Cetacean as about the first reasonable animals
of a planet the Earth.
3) The Nature has shown the ingenuity miracles al-
ready about 25 million years ago at creation of the
echo-location system and spoken language of a dolphin.
Hence the signals characteristics, obviously, are defined
by their functionality and are optimum from the point of
view of the modern state of physical acoustics.
The aspects considering of characteristics and possible
functions of the dolphins signals in this study does not
claim to be complete, but probably point out the perspec-
tiveness of their further studying.
6. Acknowledgments
The author would like to thank Nikolay Bibikov (An-
dreev Acoustical Institute, Moscow) for the ADC
(USB-3000) granting. Also, the personnel of the bio-
acoustics laboratory of sea mammals of Karadag Natural
Reserve, especially to trainers Sveta Yahno and Nadya
Zhukova for their invaluable assistance.
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