Amplitude discrimination is predictably affected by echo frequency filtering in wideband echolocating bats

Big brown bats emit wideband frequency modulated (FM) ultrasonic pulses for echolocation. They perceive target range from echo delay and target size from echo amplitude. Their sounds contain two prominent down-sweeping harmonic sweeps (FM1, ~55-22 kHz; FM2, ~100-55 kHz), which are affected differently by propagation out to the target and back to the bat. FM2 is attenuated more than FM1 during propagation. Bats anchor target ranging asymmetrically on the low frequencies in FM1, while FM2 only contributes if FM1 is present as well. These experiments tested whether the bat's ability to discriminate target size from the amplitude of echoes is affected by selectively attenuating upper or lower frequencies. Bats were trained to perform an echo amplitude discrimination task with virtual echo targets 83 cm away. While echo delay was held constant and echo amplitude was varied to estimate threshold, either lower FM1 frequencies or higher FM2 frequencies were attenuated. The results parallel effects seen in echo delay experiments; bats' performance was significantly poorer when the lower frequencies in echoes were attenuated, compared to higher frequencies. The bat's ability to distinguish between virtual targets at the same simulated range from echoes arriving at the same delay indicates a high level of focused attention for perceptual isolation of one and suppression of the other.

How frequency hopping suppresses pulse-echo ambiguity in bat biosonar

Big brown bats transmit wideband FM biosonar sounds that sweep from 55 to 25 kHz (first harmonic, FM1) and from 110 to 50 kHz (second harmonic, FM2). FM1 is required to perceive echo delay for target ranging; FM2 contributes only if corresponding FM1 frequencies are present. We show that echoes need only the lowest FM1 broadcast frequencies of 25 to 30 kHz for delay perception. If these frequencies are removed, no delay is perceived. Bats begin echo processing at the lowest frequencies and accumulate perceptual acuity over successively higher frequencies, but they cannot proceed without the low-frequency starting point in their broadcasts. This reveals a solution to pulse-echo ambiguity, a serious problem for radar or sonar. In dense, extended biosonar scenes, bats have to emit sounds rapidly to avoid collisions with near objects. But if a new broadcast is emitted when echoes of the previous broadcast still are arriving, echoes from both broadcasts intermingle, creating ambiguity about which echo corresponds to which broadcast. Frequency hopping by several kilohertz from one broadcast to the next can segregate overlapping narrowband echo streams, but wideband FM echoes ordinarily do not segregate because their spectra still overlap. By starting echo processing at the lowest frequencies in frequency-hopped broadcasts, echoes of the higher hopped broadcast are prevented from being accepted by lower hopped broadcasts, and ambiguity is avoided. The bat-inspired spectrogram correlation and transformation (SCAT) model also begins at the lowest frequencies; echoes that lack them are eliminated from processing of delay and no longer cause ambiguity.

A Virtual Switching Model for Improvemnent of Call Quality in Integrated Communication System

Poor voice quality in VoIP models during communication has been a common occurrence which VoIP users experience, this can be frustrating when users cannot communicate efficiently. Most people find it difficult to think straight when they make calls and there is an echo. In addition to this frustration, the caller’s money, time, effort, energy is all wasted without compensation of any kind. Users are also frustrated by not receiving, transmitting or misunderstanding voice messages correctly. Given the need for voice quality in calls, it is of no importance when there is no proper communication. This study aims to reduce the threat of bad calls and improve the quality of voice calls. Nonetheless, we need to raise the filter duration to a high value in some real telecom’s environments with long echo delays. But, because of high computational complexity, it is not efficient in efficiency. In this study, we suggest a solution that uses a computational formula to compensate long echo, delay, packet loss, jitter and noise. The model designed was developed using MATLAB 2019b. This approach demonstrated productivity in terms of both voice quality and system speed.

Indoor Pedestrian Self-Positioning Based on Image Acoustic Source Impulse Using a Sensor-Rich Smartphone

The ubiquity of sensor-rich smartphones provides opportunities for a low-cost method to track indoor pedestrians. In this situation, pedestrian dead reckoning (PDR) is a widely used technology; however, its cumulative error seriously affects its accuracy. This paper presents a method of combining infrastructure-free indoor acoustic self-positioning with PDR self-positioning, which verifies the rationality of PDR results through the acoustic constraint between a sound source and its image sources. We further determine the first-order echo delay measurements, thus obtaining the mobile user position. We verify that the proposed method can achieve a continuous self-positioning median error of 0.19 m, and the error probability below 0.12 m is 54.46%, which indicates its ability to eliminate PDR error, as well as its adaptability to environmental disturbances.

Natural echolocation sequences evoke echo-delay selectivity in the auditory midbrain of the FM bat, Eptesicus fuscus

Echolocating bats must process temporal streams of sonar sounds to represent objects along the range axis. Neuronal echo-delay tuning, the putative mechanism of sonar ranging, has been characterized in the inferior colliculus (IC) of the mustached bat, an insectivorous species that produces echolocation calls consisting of constant frequency and frequency modulated (FM) components, but not in species that use FM signals alone. This raises questions about the mechanisms that give rise to echo-delay tuning in insectivorous bats that use different signal designs. To investigate whether stimulus context may account for species differences in echo-delay selectivity, we characterized single-unit responses in the IC of awake passively listening FM bats, Eptesicus fuscus, to broadcasts of natural sonar call-echo sequences, which contained dynamic changes in signal duration, interval, spectrotemporal structure, and echo-delay. In E. fuscus, neural selectivity to call-echo delay emerges in a population of IC neurons when stimulated with call-echo pairs presented at intervals mimicking those in a natural sonar sequence. To determine whether echo-delay selectivity also depends on the spectrotemporal features of individual sounds within natural sonar sequences, we studied responses to computer-generated echolocation signals that controlled for call interval, duration, bandwidth, sweep rate, and echo-delay. A subpopulation of IC neurons responded selectively to the combination of the spectrotemporal structure of natural call-echo pairs and their temporal patterning within a dynamic sonar sequence. These new findings suggest that the FM bat’s fine control over biosonar signal parameters may modulate IC neuronal selectivity to the dimension of echo-delay. NEW & NOTEWORTHY Echolocating bats perform precise auditory temporal computations to estimate their distance to objects. Here, we report that response selectivity of neurons in the inferior colliculus of a frequency modulated bat to call-echo delay, or target range tuning, depends on the temporal patterning and spectrotemporal features of sound elements in a natural echolocation sequence. We suggest that echo responses to objects at different distances are gated by the bat’s active control over the spectrotemporal patterning of its sonar emissions.