Ryoji Miyahara

Phase randomization - A new paradigm for single-channel signal enhancement

This paper proposes a new paradigm with phase randomization for single-channel signal enhancement. In contrast to literatures which pursue better target signal quality, the new method tries to minimize artifacts in the residual noise. Applications of signal enhancement are revisited to highlight todays examples where environmental signal is often considered as a part of target and SNR may take a negative value. A signal example demonstrates that conventional signal enhancement with magnitude-only modification is insufficient from both objective and subjective points of view. A new framework with phase randomization as well as a specific algorithm is developed. Enhanced signals show that phase randomization is an integral component for sufficient enhancement. A subjective evaluation result demonstrates that the new paradigm with phase randomization is superior to the magnitude-only enhancement with statistically significant differences.

Tapping-noise suppression with magnitude-weighted phase-based detection

This paper proposes tapping noise suppression with a new phase-based detection. Phase slope of the input noisy signal is compared with an ideal phase slope obtained from an average of intra-frame slopes along the frequency axis. In order to cope with heavily low-pass characteristics of tapping noise spectrum, phase values are weighted with the magnitude at each frequency point. Phase unwrapping problem is alleviated by use of a rotation vector of frequency domain components. Comparison of enhanced signal spectrogram with that of clean speech demonstrates superior enhanced signal quality.

A new generalized sidelobe canceller with a compact array of microphones suitable for mobile terminals

This paper proposes a new generalized sidelobe canceller with a compact array of microphones suitable for mobile terminals. The output of the fixed beamformer (FBF) is further processed by a newly introduced decorrelation unit which has an auxiliary input signal to improve poor interference suppression of FBF in low frequencies. The output of the decorrelation unit is used as the reference signal for the adaptive blocking matrix and the input for the multi-input canceller. Because low and high frequency components are cancelled or suppressed by the decorrelation unit and FBF, better output-signal quality is obtained. Output signal comparison confirms approximately 12 dB higher interference cancellation by the new beamformer.

An auto-focusing noise suppressor for cellphone movies based on peak preservation and phase randomization

This paper proposes an auto-focusing noise suppressor (AF-NS) for cellphone movies. For relatively small clicks compared to the target signal, it consists of magnitude suppression and complementary phase modification. The input signal is analyzed in the frequency domain to detect and preserve important spectral components including peaks and their vicinities. All other components are suppressed to the environmental signal level that is estimated during absence of the important components. Residual spikes by auto-focusing noise are successfully suppressed by phase randomization. Subjective evaluation results demonstrate that the proposed AF-NS achieves scores of 1.6 and 1.8 in the 7-grade modified CMOS with statistically significant differences compared to the input noisy signal and an AF-NS with no phase randomization.

A directional noise suppressor with an adjustable constant beamwidth for multichannel signal enhancement

This paper proposes a directional noise suppressor with an adjustable constant beamwidth for multichannel signal enhancement. A directional gain based on inter-channel phase difference is combined with a spectral gain commonly used in noise suppressors (NS). The beamwidth can be specified as passband edges of the directional gain. In order to implement frequency-independent constant beamwidth, frequency-proportionate band-edge phase differences are determined for the passband. Stereo perception is preserved by weighting stereo input with the common directional and spectral gain. Evaluation with signals recorded by a commercial PC demonstrates that the signal-to-noise ratio improvement and the PESQ score for the enhanced signal are equally improved in two channels by 26.1 dB and 0.2 over a conventional NS. ILD difference between the input and the output is small when the target-signal dominates the input signal.

An auto-focusing-noise suppressor for cellphone movies based on multiple noise references

This paper proposes an auto-focusing-noise suppressor for cellphonemovies based onmultiple noise references. Auto-focusing (AF) noise generated by lens actuators is suppressed with a spectral gain calculated from a combination of multiple noise references prepared in advance. For quick adjustment to individual differences among products,mixing ratios for noise references are adaptively determined by analysis results of the input signal. For simultaneous suppression of background noise, the spectral gain for AF noise or that for background noise, whichever is smaller, is applied to the input signal for actual suppression. Simulation results demonstrate that an AF noise generated by a commercial cellphone handset is successfully suppressed with little distortion in the target signal. Sound demonstration is provided upon presentation.

Gain relaxation: A useful technique for signal enhancement with an unaware local noise source targeted at speech recognition

This paper proposes gain relaxation in signal enhancement designed for speech recognition with an unaware local noise source. An attention is drawn to a new performance degradation problem in signal enhancement combined with automatic speech recognition (ASR), which is encountered in real products with an unaware noise source. Gain relaxation, as a solution, selectively applies softer enhancement of a target signal to eliminate potential degradation in speech recognition caused by small undesirable distortion in the target signal components. Evaluation of directional interference suppression with signals recorded by a commercial PC (personal computer) demonstrates that signal enhancement over the input is achieved without sacrificing the performance for clean speech.

A directional noise suppressor with a specified beamwidth

this paper proposes a directional noise suppressor with a specified constant beamwidth. A directional gain is calculated based on interchannel phase difference and combined with a spectral gain commonly used in single-channelnoise suppressors (NSs). The beamwidth can be specified as passband edges of the directional gain. In order to implement frequency-independent constant beamwidth, frequency-proportionate band-edge phase differences are determined for the passband. Evaluation with signals recorded by a commercial PC demonstrates good agreement between the theoretical and the measured directivity. The signal-to-noise ratio improvement and the PESQ score for the enhanced signal are improved by 24.4 dB and 0.3 over a conventional NS.

An adaptive noise canceller with adaptive delay compensation for a distant noise source

This paper proposes a noise canceller with adaptive delay compensation for a distant noise source. A delay element is introduced in the noise path to offset the delay caused by the distance from the distant noise source to the reference microphone. To cope with a variety of the distance, it is controlled based on the significance of adaptive-filter coefficients. The delay is increased when the coefficients in the head are more significant than those in the tail, and vice versa. This adaptive control makes the adaptive filter with a limited number of coefficients cover the most significant part of the impulse response of the noise path, thereby achieving the best possible noise cancellation. Simulation results demonstrate superior identification capability, that leads to noise cancellation as good as that with the true amount of delay.

An auto-focusing noise suppressor for cellphone movies based on phase randomization and power compensation

This paper proposes an auto-focusing noise suppressor for cellphone movies based on phase randomization and power compensation. The input signal is analyzed in the frequency domain to detect and preserve important spectral components including peaks. All other components are suppressed to the background signal level that is estimated during absence of the important components. Residual spikes by auto-focusing noise are suppressed by phase randomization, which is not possible without phase manipulation. Power reduction by phase randomization is compensated for by an analytically obtained factor. Subjective evaluation results demonstrate that the proposed auto-focusing noise suppressor achieves a score of 1.0 in the 7-grade comparison MOS (CMOS) compared to the one without compensation with a statistically significant difference.