Daisuke Ikefuji

Weighted double sideband modulation toward high quality audible sound on parametric loudspeaker

Recently, parametric loudspeakers have been utilized to reproduce an audible sound in a particular area by an ultrasound. However, parametric loudspeakers have lower sound quality than general electrodynamic loudspeakers because it is difficult to reproduce an audible sound at lower frequency. Moreover, the reproduced sound includes harmonic distortions causing deterioration of sound quality. Thus, in this paper, we attempt to improve sound quality of parametric loudspeakers. It depends on a modulation technique for designing the amplitude modulated wave. Therefore, we propose a new modulation method to reproduce audible sound with high quality. The proposed method controls a weight of double sidebands for reducing harmonic distortions at higher frequency and emphasizing power at lower frequency. We carried out evaluation experiments to confirm the effectiveness of the proposed method. The results confirmed that the proposed method could improve sound quality of parametric loudspeakers.

Reverberation steering and listening area expansion on 3-D sound field reproduction with parametric array loudspeaker

Recently, technologies for reproducing a 3-dimensional sound field are required for providing highly realistic sensations. Therefore, we previously proposed a system with multiple parametric array loudspeakers (PAL). PALs can design sound images on walls, ceilings, and floors by using the higher directivity of ultrasound. Thus, the proposed system can easily present incoming sound from various directions. However, it is difficult to provide a realistic sensation depending on the reverberation time. In addition, the listening area of one PAL is small. In this paper, we therefore propose two approaches for overcoming these problems. First, we propose reverberation steering with indirect electrodynamic loudspeakers and PALs. We also attempt to expand the listening area of the sound image with a curved-type PAL. As a result of evaluation experiments for each proposed approach, we could confirm the effectiveness of each approach.

An investigation into the relationship between sound quality and demodulation ratio for parametric loudspeakers

Recently, parametric loudspeakers with a powerful ultrasound have been utilized for reproduction of sound to particular area. Amplitude of the ultrasound is modulated with a target audible sound. The emitted amplitude modulated wave is demodulated into the target audible sound in the air. Demodulation ratio affects sound quality of the reproduced sound with parametric loudspeakers. Moreover, demodulation ratio depends on the distance between the parametric loudspeaker and the listener. Therefore, the listener should utilize parametric loudspeakers at the suitable distance, which is required for sufficient demodulation of the amplitude modulated wave. Thus, we have proposed the criterion for measuring the demodulation ratio. However, it had not been conducted to investigate a relationship between subjective sound quality and demodulation ratio. In this paper, we investigate the relationship for estimation of the suitable distance. We carried out subjective evaluation experiment for confirming sound quality...

A design of audio spot based on separating emission of the carrier and sideband waves

Parametric loudspeaker, which utilizes an ultrasonic of non-linear interaction, is developed to achieve audio spot. The parametric loudspeaker has sharper directivity, but reflections and intercepts by emitted sounds become severe problems. This is because reflections and intercepts lead to an invasion of privacy, and become noise to other listeners except a target listener. Principle of the parametric loudspeaker can formulate as non-linear interaction of carrier and sideband waves in emitted ultrasonic sounds on air. This suggests that we can design audio spot by individually emitting the carrier and sideband waves. In the present paper, therefore, we propose the design method of audio spot with the separating emission of the carrier and sideband waves. More specifically, the audible sound is demodulated at an area where the carrier and sideband waves individually emitted from each parametric loudspeaker are overlapped. We carried out evaluation experiments to measure sound pressure level (SPL) of demod...

Estimation of demodulation ratio for the parametric loudspeaker based on spectral envelope

A parametric loudspeaker with the higher directivity transmits the sound wave to only particular area. It emits an AM (Amplitude-Modulated) wave demodulating into an audible sound wave by nonlinear interaction in the air. Therefore, longer distance is required for fully demodulating the AM wave into the audible sound wave. On the other hand, a power of the audible sound wave decays depending on the distance. Thus, the parametric loudspeaker must be utilized on the suitable distance for reproducing the fully demodulated wave with an enough power. However, no criterion has been conventionally proposed to measure the demodulation ratio in the past. Accordingly, the criterion should be formulated to measure demodulation ratio for appropriately utilizing the parametric loudspeaker. Thus in this paper, we aim at formulating it for estimation of demodulation ratio. We therefore propose the criterion based on a spectral envelope of the reproduced TSP (Time-Stretched-Pulse) with parametric loudspeaker. The propose...

Harmonic distortion measurement for a parametric loudspeaker with logarithmic time stretched pulse

A parametric loudspeaker which utilizes the ultrasound can transmit the audible sound to a particular area. However, the sound reproduced by a parametric loudspeaker contains the harmonic distortions because the sound is demodulated by the nonlinearity in the air. Thus, measuring the harmonic distortions is required to evaluate the sound quality of a parametric loudspeaker. Sinusoidal wave method has been used as the harmonic distortion measurement. In it, the harmonic distortion is measured by analyzing the integral multiplication frequency of a reproduced sine wave. Many measurements by using sine waves with each different frequency are required to measure the wideband harmonic distortions. Therefore, measuring the wideband harmonic distortions with sinusoidal wave method requires much more time. Recently, using Log-TSP (logarithmic time stretched pulse) signal was proposed to measure the wideband harmonic distortions in a short time for non-parametric loudspeakers. Thus in this paper, we attempt to mea...

Robust sound image localization for moving listener with curved-type parametric loudspeaker

Recently, technologies for reproducing a 3-D sound field are required for providing highly realistic sensations. We previously proposed a system with multiple parametric loudspeakers that have a higher directivity by using ultrasound to reproduce an audible sound in a particular area. These loudspeakers can design sound images on walls, ceilings, and floors by reflecting an emitted sound, and thus, the proposed system can easily present incoming sound from various directions. However, it is difficult to maintain the performance of sound image localization when a listener moves away from the reproduction area of the emitted sound. In this paper, we propose a sound image design method with robust localization for moving listeners. In order to constantly present the sound image localization, the method needs to steer the direction of emission in accordance with the movement of the listener. To enable this, we developed a curved-type parametric loudspeaker consisting of ultrasonic transducers arranged in an arc. The proposed method can steer the emitting direction by switching the input ultrasonic transducers without moving itself. Experimental results clearly demonstrate the effectiveness of the proposed method.

A design of control signal in reducing discomfort of the dental treatment sound based on auditory masking

In dental treatment, patients feel a strong discomfort feeling by the treatment sounds which arise by a tooth grinding. In order to add comfort to quality of life, we aim to reduce the discomfort feeling with dental treatment sounds. We previously proposed the unpleasantness reduction method based on auditory masking to reduce discomfort feeling of noise. The previously proposed method can reduce discomfort feeling by emitting a control signal to a listener, but we had focused on unpleasantness reduction to noise which has a peak frequency. Meanwhile, dental treatment sounds tend to consist of multiple spectral peaks. Therefore, in the present paper, we propose the design method of control signals for reducing discomfort feeling of dental treatment sounds which have multiple spectral peaks. More specifically, we detect the main spectral peaks which bring a discomfort feeling, and design the control signal which can mask these spectral peaks. Also, we employ the sound of running water as a source for the c...

Parametric loudspeaker for speech signal based on the combination of amplitude and frequency modulations

A parametric loudspeaker has been used for audio guidance to a specific area because it has a sharper directivity compared with the conventional electrodynamic loudspeakers. The parametric loudspeaker emits an ultrasound as a carrier wave, which is modulated with an audio signal and has large-amplitude. An audible sound is reproduced by the modulated ultrasound with large-amplitude distorted by the nonlinearity on the air. The conventional modulations have been proposed as the amplitude modulation and the frequency modulation. In the sound quality, the amplitude modulation is superior to the frequency modulation. However, in the sound pressure level, the frequency modulation is superior to the amplitude modulation. In the present paper, we especially focus on that the parametric loudspeaker will emit the speech signals for the audio guidance. Therefore, we propose new modulation method based on the combination of amplitude and frequency modulations, which are specialized for speech signals. More specifica...