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Title

Study on detectability of signals by utilizing
differences in their amplitude modulation

Author(s)Yano, Yuta; Miyauchi, Ryota; Unoki, Masashi;
Akagi, Masato

Citation

2012 International Workshop on Nonlinear
Circuits, Communications and Signal Processing(NCSP'12): 611‑614

Issue Date

2012‑03‑06

Type

Conference Paper

Text version

publisher

URL

http://hdl.handle.net/10119/10822

RightsThis material is posted here with permission of
the Research Institute of Signal Processing
Japan. Yuta Yano, Ryota Miyauchi, Masashi Unoki,
and Masato Akagi, 2012 International Workshop on
Nonlinear Circuits, Communications and Signal
Processing (NCSP'12), 2012, pp.611‑614.

Description

Japan Advanced Institute of Science and Technology

2012 International Workshop on Nonlinear Circuits,
Communications and Signal Processing
NCSP'12, Honolulu, Hawaii, USA. March 4-6, 2012

Study on detectability of signals by utilizing differencesin their amplitude modulation
Yuta Yano, Ryota Miyauchi, Masashi Unoki, and Masato Akagi
School of Information Science, Japan Advanced Institute of Science and Technology
1-1 Asahidai, Nomi, Ishikawa, 923-1292 Japan
Phone/FAX:+81-761-51-1391/+81-761-51-1149
Email: {s0810064, ryota, unoki, akagi}@jaist.ac.jp

Abstract
Auditory search experiments were conducted to investigate
the detectability of targets with regard to movements in temporal envelopes. The movements in the temporal envelopes ofsignals were defined as the mean value of slopes, i.e., the firstorder approximation of the temporal envelopes. The movements were systematically controlled by band-pass filteringon the modulation spectrum of the signals. The movementsthat we used in the experiments were 44, 154, 264, 374, 484,
594, and 704 mV/s. The movements of target signals wereset at 264, 374, 484 mV/s. The movements of backgroundsignals in each target were set to be different from the movements between target and background signals. Stimuli werecomposed of different temporal envelopes with a noise carrier. 1/2-octave band-noise as a carrier was used in which
the center frequency of the carrier was 1380 Hz. The results
obtained from auditory search experiments demonstrated thatthe detectability of each target signal could be improved whenthe movements of the target and background signals differed.
The results revealed that the difference in the movements ofthe temporal envelopes of signals affected the detectability ofthe signals.
1. Introduction

Asemi et al. [3], in a study that had a close relationship toours, carried out research on auditory search tasks. Narrowband noise and pure tones were used and temporal fluctuations in the target were controlled in their experiments ascues to investigating improvements in the detectability of target signals. Their results indicated that temporal fluctuationsin the target against background signals played a role in improving detectability.
Based on their results, Kusaba et al. investigated how muchtemporal fluctuations between the target and background signals could improve detectability of the target signal in auditory search experiments [4]. Their results suggested thatless similarity in temporal fluctuations between the target andbackground signals could improve the detectability of the target in noisy environments. However, as they used directed
narrow-band noise as stimuli in their experiments, the temporal fluctuations were not controlled.
We defined movements in our previous study and carriedout auditory search experiments by using controlled movements. The results suggested that the detectability of target
signals was improved as the difference in the movements increased. This tendency constantly appeared when the movement of the target signal was greater than that of the background signal [5]. However, this experiment had two factors
for movement and the carrier frequency, so that we could notinvestigate the factor for movement only.
We investigated the relationship between movements andthe parameters of the BP filter in this study. Based on thisinvestigation, we generated stimuli where the values for thedifference in the target for the movements and backgroundsignals were evenly distributed, and we carried out an auditory search experiment. We considered that the detectabilityof a signal was affected in this way by utilizing movements in
temporal envelopes and determined whether or not we would
be able to control the detectability of signals through movements.

Audible alarm signals are used to attract the attentionof people in many everyday activities, e.g., the beeps andmelodic sounds of electronic products that alert us of providing start and end times and the sounds of fire alarms inemergencies [1]. Therefore, these signals must be perceived
accurately and efficiently by everyone. Alarm signals withmany different stimulus signatures have been studied for thispurpose to check if they can be adequately perceived, e.g.,by Mizunami et al. [2]. There are, however, cases where
alarm signals cannot be correctly perceived in real environments because they are masked or partially masked by background noise, and only the person they are intended for knows 2. Movements in temporal envelopes of signals
when and what events have occurred. Therefore, it is important to present alarm signals in such a way that they can be 2.1. Definition of movements
correctly detected in any environment. Here, we can replace
We defined movements in the temporal envelope of a signal
the detectability of target signals with auditory search tasks.

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0
-5

(a)
0

1

2

3

-20

(c)
20

-20

40

Modulation frequency (Hz)

20

40

20
0
-20

(d)
0

20

40

bandwidth (Hz)
1.0
1.5
1.5
1.0
1.5
1.5
1.0

movements (mV/s)
88
308
528
748
968
1188
1408

Modulation Frequency (Hz)1

Amplitude

0.1

Amplitude

CF (Hz)
2.00
4.75
9.25
11.50
14.25
16.25
20.00

(b)
0

Spectrum (dB)

Filter gain (dB)

0

0

0

Modulation frequency (Hz)Time, t (s)-40Table 1: Relationship between movements and parameters of
BP filter

20

Spectrum (dB)

Amplitude

5

processed amplitude envelope was then obtained from the inverse Fourier transform shown in Fig. 1(e). This was normal(e)(f)
ized by the averaged value for amplitude to be ±0.5. Stimuli
-0.1
0
0
1
2
3
0
1
2
3
were generated by multiplying the temporal envelopes with
Time, t (s)Time, t (s)the carriers. The rising and falling edges of the stimuli werecreated as a 30-ms raised-cosine.
We systematically controlled the envelopes shown in Fig.
Figure 1: Examples of generation of stimuli: (a) white noise, 1(f) by using Eq. (1) to control movements in the temporal(b) modulation spectrum of white noise, (c) bandpass (BP) envelopes. As in the above, various movements were generfilter on modulation spectrum, (d) modulation spectrum of ated by systematically controlling their modulation spectrum
BP-filtered noise, (e) amplitude envelope, and (f) normalized using the BP filter.
amplitude envelope.
00.5

as the mean value of slopes as a first-order approximation of
temporal envelopes [5].
v=

N
A0 X |Pn − Pn−1 |,N − 1 n=2 Tn − Tn−1(1)where Pn represents the values of peaks/dips in temporal envelopes, Tn is the time, and N is the number of peaks/dips.
Here, A0 is a normalized factor and this is set to be the output reference voltage (using the TDT SystemIII and SANSUI
AU-α 907MR Integrated Amplifier). The A0 in this experiment was 88 mV. Therefore, v was in millivolts per second.
2.2. Control of movements

2.3. Relationship between movements and parameters of
BP filter
We investigated the detectability of signals based on differences in the movements of target and background signals inthis study. To do this, we needed to generate stimuli where
the differences in movements became equal. We calculated
the values for the movements of temporal envelopes by BP
filtering, which used various CFs and bandwidths for the BP
filter, to investigate the relationship between the movements
and parameters of the filter. Table 1 summarizes the relationship between the movements and parameters of the BP filter.
Furthermore, Figure 2 plots the distribution in the values of
movements obtained from each BP filtering on the modulation spectrum. We pegged the mean of values for movements
at a movement obtained from BP filtering on the modulation
spectrum. The CF and bandwidth of the BP filter were set insuch a way that each value for different movements was 220
mV/s.
We found from this figure that the movements tended toincrease commensurately as the CF of the filter increased.
Therefore, we could systematically control the movements byvarying the parameters of the filter.

We systematically controlled the movements defined above
with by bandpass (BP) filtering on the modulation spectrum
as follows. We assumed that signals could be expressed bymultiplying the temporal envelope with the carrier. Here,band-noise was used as the carrier.
Figure 1 shows an example of the generation of stimuli
that we used in the auditory search experiment. White noise
was used to generate the stimuli, as shown in Fig. 1(a). Fig- 3. Auditory search experimenture 1(b) shows the modulation spectrum of (a). Figure 1(c)shows the characteristics of the BP filter at the modulation 3.1. Aim
frequency. This filter has a bandwidth of 2.5 Hz at the CF of 2
We carried out an auditory search experiment for the target
Hz. The processed modulation spectrum was obtained by BP
filtering on the modulation spectrum shown in Fig. 1(d). The and background signals with different movements added to- 612 -

Figure 2: Distribution in movements obtained from modulation spectrum controlled by BP filtering.

Figure 3: Experimental apparatus.

investigate the detectability of the target with regard to move- 3.4. Apparatus
ments in temporal envelopes.
Figure 3 has a diagram of the apparatus we used in theexperiment, which was carried out in a sound-proof room.
3.2. Stimuli
Stimuli were generated by Tucker-Davis Technologies (TDT)
System III and presented to each subject through an amplifier
The movements in temporal envelopes that we used in the (SANSUI, AU-α) and headphones (Sennheiser HDA200).
experiment were 44, 154, 264, 374, 484, 594, and 704 mV/s. Subjects’ responses were recorded through the response box.
Three of them–264, 374, and 484 mV/s–were used as target
signals. The movements of background signals in each target
were set to be different from the movements between target 4. Results
and background signals. When the movement of the target
We obtained the detectability of the target signal, i.e., d0 ,was 264 mV/s, the movements of the background were 44,154, 374, and 484 mV/s. When the movement of the target from the results of the assessments done by the participants.
was 374 mV/s, the movements of the background were 154, There were four classifications of the results for the assess264, 484, and 594 mV/s. When the movement of the target ments: Hit (they pressed “Y” when there was a target), Miss
was 484 mV/s, the movements of the background were 264, (they pressed “N” even though there was a target), False
374, 594, and 704 mV/s. Stimuli were composed of different Alarm (they pressed “Y” even though there was no target),temporal envelopes with a noise carrier. 1/2-octave band- Correct Rejection (they pressed “N” when there was no tarnoise as a carrier was used in which the center frequency of get). Greater values for d0 indicated that the target signal was
easily detected.
the carrier was 1380 Hz.
Figure 4 plots the detectability of the target signal obtainedbyusing the difference between movements in the temporal
3.3. Procedureenvelopes of the target and background signals. The moveThere were two kinds of assessments in the auditory search ment in target signals was 264 mV/s. Figure 5 plots the deexperiment, i.e., positive and negative. Stimuli as the tar- tectability of target signals when the movement of the target
get and background signals were simultaneously presented to was 374 mV/s. Figure 6 plots the detectability of target sigthe participants via headphones in the positive assessments. nals when the movement of the target was 484 mV/s.
The results demonstrated that the detectability of target sigStimuli as background signals and band-noise in which movement was not controlled were simultaneously presented to nals was improved when the movements of the target andthe participants in the negative assessments. The participants background signals differed. They also suggested that the tarwere required to determine whether they heard the target sig- get signals were easily detected by applying different movenal with the background signal and to press a “Y (yes)” or ments to the target and background signals.
“N (no)” button on the response box. Before the participants
We used band-noise that had the same CF and bandwidth
started the sessions in this experiment, a target signal was as the carrier of the target and background signals in this exrepetitively presented to them so that they could learn the periment. The target and background signals passed throughtarget signal that would be presented in the session. There the same auditory filter under these conditions. This indicatedwere a total of 240 trials in the session (three target signals that these two signals were decomposed into one component
× four background signals × two assessments (positive and as one sound. Thus, it was extremely difficult to separate thenegative) × ten repetitions). These trials were randomly pre- two signals. However, under such difficult conditions, thesesented.
results suggest that we could perceptually separate two sig-

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Figure 4: Detectability of target signals obtained by using Figure 6: Detectability of target signals obtained by using
the differences in movements (movement of target was 264 the differences in movements (movement of target was 484
mV/s).
mV/s).
The auditory search experiments were carried out by using
target and background signals with different movements. The
results demonstrated that the detectability of target signals
could be improved when the movements of the target andbackground signals differed. This indicated that the amplitude modulation of signals was closely related to the detectability of target signals. We discovered that the detectability of signals could be controlled by utilizing differences inmovements.

Acknowledgments
Figure 5: Detectability of target signals obtained by using This work was supported by a Grant-in-Aid for Young Scienthe differences in movements (movement of target was 374 tists (B) (No. 21730584).
mV/s).
References
nals and detect a target signal by perceiving the amplitude
modulation of the signals.
We obtained results in our previous study where the detectability of target signals was improved as the difference
in movements increased. However, there was little to distinguish the detectability of signals in these results, in comparison with cases where the difference in movements was
110 mV/s and cases where the difference in movements was
220 mV/s. This was attributed to the fact that we could completely separate the two signals when the difference in movements between the target and background signals was only
110 mV/s, so that detectability remained constant even if weused further differences. We did not examine perceptual differences in movement in this experiment. Therefore, we needto set experimental conditions in investigations that are notbased on physical but perceptual differences in movements tofind how differences in movements affect the detectability oftarget signals.

[1] JIS S 0013, Guidelines for the elderly and people with disabilities - Auditory signals on consumer products, 2002.
[2] T. Mizunami, K. Kurakata, H. Shimosako, and K. Matsushita,“ Further examination of ON/OFF temporal patterns of auditory signals (completion signals and attention signal) recommended in JIS S 0013,” J. Ergonomics, 40(5), 264–271, 2005.
[3] N. Asemi, Y. Sugita, and Y. Suzuki, “ Auditory search asymmetry between normal Japanese speech sounds and timereversed speech sounds distributed on the frontal-horizontal
plane,” Acoust. Sci. &Tech. 24, 145–147, 3 (2003).
[4] M. Kusaba, M. Unoki, and M. Akagi, “ A Study on detectability of target signal in background noise by utilizing similarityof temporal envelopes in auditory search,” Proc. NCSP’08, 13–
16, 2008.
[5] Y. Yano, R. Miyauchi, M. Unoki, and M. Akagi, “ Study on
detectability of target signal by utilizing differences between
movements in temporal envelopes of target and backgroundsignals,” Proc. NCSP’11, Tianjin, China, 231–234, Mar. 2011.

5. Conclusion
We defined movements in the temporal envelopes of signals and proposed a method of controlling these movements.

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