Showing papers on "Noise published in 1989"

Intercom apparatus for integrating disparate audio sources for use in light aircraft or similar high noise environments

Abstract: Intercom apparatus having stereo amplifiers adapted for connection to one or more headsets. A plurality of headset output and microphone input connections are provided. Each microphone input includes a separate microphone switch and audio detector whereby only microphone inputs having voice audio thereon are activated. Stereo entertainment and aircraft radio audio inputs are provided. An aircraft radio audio detector is interfaced, along with the various microphone audio detectors, to entertainment partial mute circuitry whereby the presence of a voice or radio audio signal lowers the amplitude of the entertainment input. Microphone and aircraft radio partial mute circuitry are interfaced through a priority selector switch with respective microphone and radio signal detectors. The priority selector switch is a two position, center off arrangement whereby, in one position, aircraft radio signals partially mute microphone signals and in the second position microphone signals partially mute aircraft radio signals. In the center off position no cross muting occurs and the respective signals sum in conventional manner.

Insect hearing in the field. III: Masking by noise

Abstract: Summary1.Hemisaga denticulata andMygalopsis marki are two sympatrically occurring species of bushcricket. Both also have almost complete overlap in their song frequencies (Fig. 2). However, the temporal pattern of their respective songs differs considerably, males ofM. marki sing continuously compared with short bursts of song produced by males ofH. denticulata. A comparative study between two populations ofH. denticulata showed that in the presence of singing males ofM. marki, the song ofH. denticulata was suppressed (Fig. 5, Table 1). Furthermore, song interference was also demonstrated neurophysiologically in the field using the response of the omega-neuron as a ‘biological microphone’ (Fig. 4).2.In aggregations ofH. denticulata males alternate their chirp pattern, and this behaviour was used as an assay in the laboratory to test the susceptibility of intraspecific communication to biological noise. It was concluded that the precise alternating pattern between two males is significantly affected by noise (Fig. 6).3.Neurophysiological experiments performed in the laboratory revealed a strong masking effect by biological noise on the perception of the conspecific signal within the afferent auditory pathway (Figs. 7, 8). This experiment when conducted in the field exhibited similar masked responses in the omega-neuron (Figs. 9, 10).

Acoustic-phonetic characteristics of speech produced in noise and while wearing an oxygen mask.

Abstract: The present study investigated changes in the prosodic and acoustic–phonetic features of isolated words by four male talkers speaking in quiet and in pink noise at a level of 95 dB SPL. Speech samples were collected both with and without an oxygen mask. Changes in duration, fundamental frequency, total energy, and formant center frequency were analyzed. In addition to the expected changes of increased pitch and amplitude associated with speaking in noise without an oxygen mask, significant effects were found (particularly in the formant center frequencies) as a result of using the oxygen mask. When the oxygen mask was employed, no further significant changes were caused by adding noise to the speaking situation.

Enhancing speech degrated by additive noise or interfering speakers

Abstract: The author examines some of the ways that speech signals, subjected to certain degradations (e.g. additive noise, interfering speakers, bandlimiting, single-channel data), can be processed to increase the likelihood of being correctly understood. He concentrates on applications that involve monaural listening. He treats spectral and time-domain subtraction techniques, methods involving fundamental frequency tracking, and enhancement by resynthesis. >

The noise bandwidth of sampled data systems

Abstract: The effect of aliasing on sampled noise power measurements is investigated. It is shown that although aliasing does not bias noise power measurements, it can significantly increase the measurement variance. The equivalent noise bandwidth (EENBW) of a sampled data system is defined by equating the mean and variance of the noise power measurement to those of a system with a rectangular spectral response. With this definition, which is shown to be consistent with that for analog systems, it follows that the ENBW is bounded by the smaller of the analog ENBW or half the sampling frequency. Practical examples of sampled-data systems are used to demonstrate the increased variance, integration time, and noise spectral density that accompany aliasing. >

High-quality reception indicating circuit for fm receivers

Abstract: The reception of FM broadcast signals having a selected high sound quality is determined according to criteria including a low noise level and the absence of interference. The high quality information is employed to terminate a scan tuning operation or to activate an ultrasonic noise filter to improve listening quality of the FM audio output. The absence of noise and interference is determined by examining a particular frequency range from the FM field intensity line generated by an intermediate frequency circuit.

The effects of subtractive-type speech enhancement/noise reduction algorithms on parameter estimation for improved recognition and coding in high noise environments

Abstract: The authors present the results of a study designed to investigate the effects of subtractive-type noise reduction algorithms on LPC-based spectral parameter estimation as related to the performance of speech processors operating with input SNRs of 15 dB and below. Subtractive noise preprocessing greatly improves the SNR, but system performance improvement is not commensurate. LPC spectral estimation is affected by the character of the residual noise which exhibits greater variance and spectral granularity than the original broadband noise. The study shows that removing less than the full amount of noise and whitening it improves spectral estimation and speech device performance. Techniques and performance results are presented. >

A comparative study of cepstral lifters and distance measures for all pole models of speech in noise

Abstract: After a brief overview of the techniques utilized, the authors evaluate perceptually based linear prediction (PLP) analysis, and then report the results of a comparative study of several front-ends in the case of speech produced in quiet and noisy environments (Lombard effect). Several all-pole models of speech using various lifters and distance measures are compared in various noise conditions. The main conclusions of this research are: (1) when speech is produced in a quiet environment and in speaker-dependent automatic speech recognition (ASR), the cepstral projection measure significantly improves recognition scores for the three all-pole models considered (for clean reference and noisy test templates), with the best results obtained with the LP analysis (for SNR=5 dB); (2) when speech is produced in a quiet environment and in speaker-dependent and cross-speaker ASR, the optimal filter is a function of the SNR of the test and the reference templates; and (3) when speech is produced in noise and in speaker-dependent ASR, the PLPRPS front-end is the best, and a low model order of the analysis is suitable. >

Classification of audio signals on a telephone line

Abstract: This telephone solicitation system provides automatic dialing and call-progress detection. Audio signals on the line are analyzed to recognize network operation tones, noise bursts, and speech. A "sample" is the total number of crossings during a 25 millisecond period. A "window" is a sequence of eight samples analyzed for spectral and time patterns.

Spectral estimation using a log-distance error criterion applied to speech recognition

Abstract: A novel algorithm is presented for the estimation of a signal in noise. The distortion criterion used is based on the distance between log spectra. In many signal-processing applications, such as speech recognition, log spectra are much closer to the parameters used in a discriminator than power spectra. Therefore, it is believed that this spectral estimation technique should lead to better results than previously developed techniques such as spectral subtraction. The present technique performed better than spectral subtraction in noise immunity experiments on the IBM isolated word speech-recognition system, although at the expense of additional computational requirements. >

Radio with message reception and ambient noise level controlled indicator

Abstract: A radio (10) measures and stores (16, 18) the ambient sound (or noise) level of its environment. When a message is received, the current noise (or sound) level is compared to a threshold (56). If the ambient noise level is such that an audible tone may not be heard by the radio user, a silent alert is automatically activated (62) regardless of whether the silent enunciator has been previously selected (enabled) by the radio user. In another aspect of the present invention, if the ambient noise level is such that an audible tone may be inappropriate (i.e., library, courtroom, or certain hospital areas), the silent alert is also automatically activated regardless of whether the silent enunciator is enabled so as not to disturb others.

Interactive factors in consonant confusion patterns

Abstract: Confusion patterns among English consonants were examined using log‐linear modeling techniques to assess the influence of low‐pass filtering, shaped noise, presentation level, and consonant position. Ten normal‐hearing listeners were presented consonant–vowel (CV) and vowel–consonant (VC) syllables containing the vowel /a/. Stimuli were presented in quiet and in noise, and were either filtered or broadband. The noise was shaped such that the effective signal level in each (1)/(3) octave band was equivalent in quiet and noise listening conditions. Three presentation levels were analyzed corresponding to the overall rms level of the combined speech stimuli. Error patterns were affected significantly by presentation level, filtering, and consonant position as a complex interaction. The effect of filtering was dependent on presentation level and consonant position. The effects stemming from the noise were less pronounced. Specific confusions responsible for these effects were isolated, and an acoustical interaction is suggested, stressing the spectral characteristics of the signals and their modification by presentation level and filtering.

Speech operated noise attenuation device

Abstract: A speech operated noise attenuation device (SONAD) includes circuitry to measure the noise level in an audio channel. The output of the noise measurement circuitry provides a control signal to an audio attenuator which varies the intersyllable attenuation of the background noise according to the noise level present in the audio.

Background noise and lip-reading ability.

Abstract: The main aim of this pilot experiment was to determine whether background noise affects the lip-reading ability of normally hearing people Ten university students took part in a lip-reading test presented both in the quiet and with two types of competing noise The first type of noise used was speech-shaped, continuous and with a steady intensity level The second type was again continuous but with frequent and intermittent peaks of energy (classroom noise) It was found that the second type of noise had a significantly adverse effect on lipreading ability Further experimentation with hearing-impaired subjects was suggested

Masked threshold changes associated with angular separation of noise and signal sources.

Abstract: Threshold changes associated with separating a signal source and a masking white noise source from 0° to 90° were determined for 0.5, 1 and 8 kHz pure tones and click trains. No changes occurred for the 0.5 and 1 kHz pure tones. Masked thresholds of 8 kHz pure tones and click trains decreased linearly by 9 and 13 dB respectively as angular separation was moved from 0° to 90°. Changes in click train stimuli masked thresholds did not change significantly when the ear directed toward the masking source was occluded (11 dB drop at 90°). The absence of changes at low frequencies and the similarity in magnitude of the changes in signals containing high frequency components with the reponses to the monaural click trains, suggests that the threshold changes can be attributed to a head shadow effect. The casting of a sound shadow effectively lowers the noise level on the shielded side. These findings question the importance of cross-correlation techniques when detecting signals in noise.

Automatic broadcast equipment

Abstract: PURPOSE:To prevent a trouble such as hard of listening due to too low sound volume or too much sound volume by controlling the sound volume of automatic broadcast having a prescribed content by a broadcast command automatically in response to the status change in the speaker installing environment. CONSTITUTION:A noise data signal(environment state signal) 8a is fetched via a microphone 9 and a noise detection circuit 8, the sound volume in response to a noise data signal 8a is decided by a sound volume setting processing program stored in a memory 6C and a sound volume setting data signal 6b is outputted via an output circuit 6D. A sound volume setting circuit 7 outputs a sound volume control signal 7a based on the sound volume setting signal 6b, the gain of an amplifier circuit 4 is adjusted and the sound volume of a speaker 5 is a sound volume in response to the environment state. A broadcast command signal 1a is outputted as the sound data signal 6a via an input circuit 6B and the output circuit 6D. The voice synthesis circuit 3 converts the voice data signal 6a into the voice signal 3a and amplified by the amplifier circuit 4 subject to gain adjustment by using a sound volume control signal 7a and the content corresponding to a broadcast command signal 1a is broadcast in a sound volume in response to the environment state from a speaker 5.

Speech enhancement for hearing aids using adaptive beamformers

Abstract: The author presents two techniques based on adaptive noise canceling to suppress the ambient noise in hearing aids. The first technique uses two microphones and gives very good results in the case of one noise source. If two noise sources are situated at the same side of the head, there is also noise suppression, although less effective than with only one noise source. In the second technique the author creates notches in the directivity pattern of the filter when two uncorrelated noise sources are situated at opposite sides of the head by introducing an adaptive noise canceler using three microphones. The techniques were evaluated in real time using a specially developed board plugged into a personal computer. Preliminary results are presented. >

Half-tone image generator using white noise source

Abstract: A half-tone binarization generator that produces high-quality half-tone binarization images by converting multilevel brightness information into sets of black and white bitonal data by adding noise to the multilevel brightness information and using a thresholding technique.

Noise removing device

Abstract: PURPOSE:To effectively remove a noise to individual listeners by disposing an auxiliary speaker for removing the noise near to the listener on a noise removing device used for an audio device disposed on a car or the like. CONSTITUTION:In the audio device 1, the signal of a cassette player 1a is amplified by an amplifier 1b and reproduced by the speaker 1c. The noise in an engine room is collected by a microphone 2 disposed in the engine room to generate the cancel sound of the engine noise from the auxiliary speaker 5 through a filter 3, an amplifier 4. Since a distance between the ear of the listener and the auxiliary speaker 5 is shortened by disposing the auxiliary speaker 5 at both the sides of the head rest 6 of respective chairs, the noise is effectively removed at any position.

Held music history circuit

Abstract: A circuit is provided which gauges the amount of significant high-frequency spectral energy in the very recent history of the program material and ignores the effects of short noise bursts and other transients associated with FM reception in the moving vehicle. The circuit provides an output voltage which can be used to adjust the attack characteristics of an audio processor.

Limitations on the detectability of spread-spectrum signals

Abstract: The standard analysis of the radiometric detectability of a spread-spectrum signal assumes a background of stationary white Gaussian noise whose power spectral density can be measured very accurately. This assumption yields a fairly high probability of interception, even for signals of short duration. Using a generalization of the detection scenario, the authors demonstrate that realistic detection of these signals by a wideband radiometer can be considerably more difficult than is indicated by the standard result. The generalized result is then used to consider the realistic effectiveness of optimal detection of low-SNR direct-sequence pseudonoise waveforms. >

Frequency discrimination near the spectral edge of simultaneous and forward maskers

Abstract: The effects of the presence of an amplitude discontinuity in the spectrum of a noise masker on frequency discrimination performance were examined. First, detection thresholds as a function of masker level were obtained for pure‐tone signals masked by either simultaneous or forward white and low‐pass maskers. Then frequency discrimination thresholds were obtained using four masker levels that were chosen to yield predetermined masked thresholds, with signal levels corresponding to each of three sensation levels above these masked thresholds. The principal results indicate that frequency discrimination is poorer in simultaneous low‐pass noise than in simultaneous white noise, and that this difference in performance increases with increasing sensation level and with increasing masker level. These results are inconsistent with an explanation based on the pitches generated at spectral edges (‘‘edge pitch’’), pitch shifts, or disruption of phase‐locking information, but are generally consistent with an explanation based on lateral suppression. It is proposed that a release from suppression may occur in filtered noise backgrounds at high noise levels and at high sensation levels. The reduced suppression may result in poorer frequency discrimination due, in part, to reduced signal detectability.

Sound exposures and hearing thresholds of musicians in a major symphony orchestra

Abstract: Seventy noise dosimetry samples were obtained for musicians during rehearsals and performances of a major symphony orchestra. Audiograms were obtained for 59 musicians. The Leq during measurement periods ranged from 76–102 dBA (median = 90dBA), corresponding to on‐the‐job daily equivalent values of 72–98 dBA (median = 86 dBA). Using the ISO 1999.2 model, this exposure would be expected to produce 5–8 dB of NIPTS after 30 yr for typical ears (0.5 fractile) or 8–10 dB of NIPTS for very susceptible ears (0.05 fractile). The musicians' average thresholds were better than those for age‐matched reference nonindustrial noise‐exposed populations without occupational noise exposure, and only slightly worse than those for highly screened populations representing aging alone. However, audiogram patterns indicated a slight notch, suggesting a contribution from NIPTS. Bilaterally averaged thresholds for musicians in different instrument sections were essentially equivalent, but violinists and violists grouped together...

Audio data output circuit

Abstract: PURPOSE:To prevent the generation of pop noise by allowing a fade muting processing circuit to constitute an audio data processing in a frame boundary at the time of variable speed reproducing of a digital audio tape deck. CONSTITUTION:Reproduced digital audio data are inputted from an input terminal 9 and a fade muting ON signal and a fade muting OFF signal for controlling the fade muting processing circuit 10 are respectively inputted from terminals 11, 12. When the output of an OR gate 13 is high potential, a data selector 14 selects the output of the circuit 10. When the reproduced digital data are PD(i) and muted audio data are AD(i), the circuit 10 executes processing for obtaining the AD(i) by multiplying a value obtained by raising a constant X(X<1) to k-th power by the PD(i), so that AD is gradually reduced and finally goes to zero. Fade muting OFF is similarly processed and goes to a continuous signal at a zero level.

Microphone audio signal processing circuit

Abstract: PURPOSE:To suppress the recording of microphone noise and to reduce unpleasant noise at reproduction by controlling the circuit in a manner of decreasing the amplification factor of the variable gain amplifier circuit amplifying a microphone audio signal when the audio signal outputted from a microphone is small and noise from the microphone is dominant. CONSTITUTION:An audio signal from the microphone 1 is given to a band pass filter 2 where an undesired band signal such as wind noise is attenuated and the result is given to a variable gain amplifier circuit 11. Then the output signal of the band pass filter 2 is amplified by a preamplifier circuit 12 and fed to a microphone audio signal level detection circuit 13. A DC signal in response to the microphone audio signal level is outputted from the microphone audio signal level detection circuit 13 and fed to an amplification factor control circuit 14. When the audio signal outputted from the microphone is small and noise from the microphone is dominant, the amplification factor control circuit 14 detects by using the output signal from the microphone audio signal level detection circuit 13 and gives an output signal to command the decrease of the amplification factor to the variable gain amplifier circuit 11.

Noise in images of very bright sources

Abstract: Restricted Access. Synthesis imaging in radio astronomy, A collection of Lectures from the Third NRAO Synthesis Imaging Summer School, Eds. Richard A. Perley, Frederic R. Schwab, and Alan H. Bridle. Published by the Astronomical Society of the Pacific, vol. 6, San Francisco, 1989.

Spectrally efficient digital broadcast systems operated in a phase noise environment

Abstract: High spectral efficiency combined with power efficiency, is a requirement for high speed digital broadcast satellite systems. The effect of the recovered carrier phase noise and the nonlinearity on the performance of 16-QAM (quadrature amplitude modulation) and staggered 16-QAM is investigated and compared. It is found that for the phase noise, 16-QAM is more degraded for a roll-off factor of less than 0.4. For roll-off factor of more than 0.8, staggered 16-QAM has superior performance. For the nonlinearity staggered 16-QAM is more sensitive for a roll-off factor of less than 0.4. It is concluded that coincident 16-QAM is suitable for spectrally efficient digital broadcast systems. >

Excess noise in chromium silicides

Abstract: Mesure du bruit en 1/f des films a base de siliciures. Pour se faire/on etudie plus particulierement la densite spectrale du bruit normalisee