6 results about "Noise power spectrum" patented technology

The application discloses a laser phase noise measurement method based on delay self-heterodyne and digital demodulation, and relates to the technical field of laser measurement, and comprises the following contents: after being adjusted by a variable optical attenuator, to-be-measured laser is divided into a frequency shift arm and a delay arm, the frequency shift arm is frequency-shifted by an acousto-optic modulator, the delay arm is delayed by a delay optical fiber, and original electric beat frequency signals are obtained by a balanced photoelectric detector after the two arms are coupled; homologous and synchronous quadrature demodulation is carried out on the original electric beat frequency signals, envelope credibility judgment and abnormal sample repair are combined, and a continuous differential phase sequence is obtained; actual optical time delay is determined according to the beat frequency spectrum characteristics and the continuous differential phase sequence, and a differential phase power spectral density is formed; then, transmission relationship conversion is carried out according to the actual optical time delay, bounded spectrum compensation is implemented on a zero point neighborhood and a low credibility frequency point, and an intrinsic phase noise power spectral density is obtained. The application can improve the stability, continuity and result credibility of phase noise measurement under the condition of short delay.

This invention belongs to the field of noise floor reduction and proposes a frequency-band noise floor reduction method based on a spectrum analyzer. This invention can solve the problems of uneven noise power distribution and excessive noise power estimation. It includes the following steps: acquiring the noise floor signal of the spectrum analyzer, wherein the noise floor signal is a low-pass or band-limited white noise signal with a specified bandwidth; dividing the specified bandwidth into a first number of sub-segments and dividing the signal power before denoising into a first number of sub-segments; estimating the noise power under the specified bandwidth and dividing it into a first number of sub-segments; denoising each sub-segment and calculating the noise power spectral density of each sub-segment after denoising based on the bandwidth after segmentation, the signal power before denoising after segmentation, and the estimated noise power after segmentation; and ensuring that the noise power spectral density after denoising is not negative by using the compression factor method or the square root method.

The application discloses a ship radiated noise power spectrum measurement method based on frequency difference beam forming, comprising the following steps: obtaining a to-be-measured radiated noise signal received by a base array; constructing a difference frequency signal through the conjugate product of the to-be-measured radiated noise signal and a reference frequency signal; performing beam forming on the constructed difference frequency signal based on the difference frequency, and calculating the amplitude of the beam output signal of the difference frequency signal; correcting the amplitude of the beam output signal of the difference frequency signal by using the amplitude of the reference frequency signal to obtain the amplitude of the to-be-measured radiated noise signal, and calculating the power spectrum of the to-be-measured radiated noise signal. The application converts the signal outside the design frequency band of the base array to the inside of the design frequency band to perform beam forming, improves the array gain, better suppresses the environmental noise, improves the measurement performance of the base array on the radiated noise outside the design frequency band, greatly expands the frequency band width of the ship radiated noise measurement, and can realize the measurement of the radiated noise with a larger bandwidth by using a smaller aperture array.

The application discloses a fish culture net cage noise tracking method based on optimal smoothing and minimum statistics, and relates to the field of aquaculture. According to the frequency energy distribution characteristics of an input signal, the application automatically adjusts a smoothing parameter, smoothes a power spectrum, and combines minimum value deviation compensation to estimate a smoothing result, so that accurate tracking of a background noise signal is realized, noise power spectrum components can be effectively extracted in a complex noise environment, and additional detection for a target signal is not needed. The application introduces a time-frequency adaptive smoothing parameter mechanism, and fuses minimum statistics to track and estimate a background noise power spectrum. Without training data, the application can effectively determine the noise condition of a sampling signal in a complex noise condition, and solves the problems that existing noise separation methods have poor performance when separating non-stationary noise and need a large amount of training data.

A system and method of harmonizing computed tomography (CT) images to reduce variability introduced by differing reconstruction kernels. The method includes acquiring a CT image of a plurality of regions of a patient. The method includes calculating, by a processing device, a noise power spectrum (NPS) of a uniform region among the plurality of regions. The method includes selecting, from a library of reconstruction kernels, a first reconstruction kernel based on the NPS of the uniform region of the plurality of regions. The method includes generating a harmonized CT image based on the first reconstruction kernel and the CT image.

This invention relates to the field of fan, speaker, and light design and control technology, and discloses a low-noise design method for a speaker fan based on fan noise. The method includes receiving the original audio signal, generating an audio power spectrum, and extracting low-frequency transient features; calculating the instantaneous masking threshold using a psychoacoustic model, and then inversely shaping the allowable noise power spectrum of the fan motor to generate a target fan spectrum; generating a fan drive signal based on the target spectrum using a random spread spectrum algorithm, and constructing an airflow velocity vector by combining the angular velocity fed back from the motor and the duct parameters; calculating the phase compensation amount based on the airflow velocity vector to generate a phase correction signal, and then combining the low-frequency transient features with an anti-phase aerodynamic impedance compensation component to synthesize a speaker signal; finally, driving the fan motor and speaker unit to operate synchronously. This invention utilizes the auditory masking effect to achieve invisible fan operation and cancels the interference of airflow on sound waves through flow field mapping and phase pre-distortion, achieving synergistic optimization of the sound field and airflow field.