Favorable Signal-to-noise Ratio Research Articles

Analysis of theoretical machined surface roughness profile after sawing solid oak wood (Quercus robur L.) along the grain with a circular saw

ABSTRACT The article presents an analysis of the influence of simulated circular saw teeth marks profile in relation to the anatomical roughness of solid oak wood (Quercus robur L.) on machining roughness after sawing along the grain with a circular saw in order to better understand this relationship and to improve the knowledge how this two factors can be separated for further analysis in real-world sawing and to try to quantify the minimum theoretical tooth mark height that could be distinguished from anatomical roughness of wood. The signal-to-noise ratio (SNR) of simulated circular saw teeth mark signal in relation to measured anatomical roughness signal of solid oak wood was used to determine the level at which saw teeth marks could have a meaningful impact on machined surface roughness. From the analysis it can be concluded that SNR values even as low as −13 dB can have enough information to be used for frequency analysis and filtering out of tooth marks signal. Averaging and longer sampling lengths provide much better SNR values and provide the frequency spectrum of the structural roughness signal of solid oak wood with the highest amplitude of less than 0.5 μm. If more favorable SNR values are to be obtained, sampling lengths should be much longer than what is standardly used and recommended in ISO 3274: 1996 (in this research cumulative sampling length of 600 mm was used).

Listening Over Time: Single-Trial Tonic and Phasic Oscillatory Alpha-and Theta-Band Indicators of Listening-Related Fatigue.

ObjectivesListening effort engages cognitive resources to support speech understanding in adverse listening conditions, and leads to fatigue over the longer term for people with hearing loss. Direct, neural measures of listening-related fatigue have not been developed. Here, event-related or phasic changes in alpha and theta oscillatory power during listening were used as measures of listening effort, and longer-term or tonic changes over the course of the listening task were assessed as measures of listening-related fatigue. In addition, influences of self-reported fatigue and degree of hearing loss on tonic changes in oscillatory power were examined.DesignParticipants were middle-aged adults (age 37–65 years; n = 12) with age-appropriate hearing. Sentences were presented in a background of multi-talker babble at a range of signal-to-noise ratios (SNRs) varying around the 80 percent threshold of individual listeners. Single-trial oscillatory power during both sentence and baseline intervals was analyzed with linear mixed-effect models that included as predictors trial number, SNR, subjective fatigue, and hearing loss.ResultsAlpha and theta power in both sentence presentation and baseline intervals increased as a function of trial, indicating listening-related fatigue. Further, tonic power increases across trials were affected by hearing loss and/or subjective fatigue, particularly in the alpha-band. Phasic changes in alpha and theta power generally tracked with SNR, with decreased alpha power and increased theta power at less favorable SNRs. However, for the alpha-band, the linear effect of SNR emerged only at later trials.ConclusionTonic increases in oscillatory power in alpha- and theta-bands over the course of a listening task may be biomarkers for the development of listening-related fatigue. In addition, alpha-band power as an index of listening-related fatigue may be sensitive to individual differences attributable to level of hearing loss and the subjective experience of listening-related fatigue. Finally, phasic effects of SNR on alpha power emerged only after a period of listening, suggesting that this measure of listening effort could depend on the development of listening-related fatigue.

Personalizing Transient Noise Reduction Algorithm Settings for Cochlear Implant Users.

Objectives:Speech understanding in noise is difficult for patients with a cochlear implant. One common and disruptive type of noise is transient noise. We have tested transient noise reduction (TNR) algorithms in cochlear implant users to investigate the merits of personalizing the noise reduction settings based on a subject’s own preference.Design:The effect of personalizing two parameters of a broadband and a multiband TNR algorithm (TNRbb and TNRmb, respectively) on speech recognition was tested in a group of 15 unilaterally implanted subjects in cafeteria noise. The noise consisted of a combination of clattering dishes and babble noise. Each participant could individually vary two parameters, namely the scaling factor of the attenuation and the release time (τ). The parameter τ represents the duration of the attenuation applied after a transient is detected. As a reference, the current clinical standard TNR “SoundRelax” from Advanced Bionics was tested (TNRbb-std). Effectiveness of the algorithms on speech recognition was evaluated adaptively by determining the speech reception threshold (SRT). Possible subjective benefits of the algorithms were assessed using a rating task at a fixed signal-to-noise ratio (SNR) of SRT + 3 dB. Rating was performed on four items, namely speech intelligibility, speech naturalness, listening effort, and annoyance of the noise. Word correct scores were determined at these fixed speech levels as well.Results:The personalized TNRmb improved the SRT statistically significantly with 1.3 dB, while the personalized TNRbb degraded it significantly by 1.7 dB. For TNRmb, we attempted to further optimize its settings by determining a group-based setting, leaving out those subjects that did not experience a benefit from it. Using these group-based settings, however, TNRmb did not have a significant effect on the SRT any longer. TNRbb-std did not affect speech recognition significantly. No significant effects on subjective ratings were found for any of the items investigated. In addition, at a constant speech level of SRT + 3 dB, no effect of any of the algorithms was found on word correct scores, including TNRmb with personalized settings.Conclusions:Our study results indicate that personalizing noise reduction settings of a multiband TNR algorithm can significantly improve speech intelligibility in transient noise, but only under challenging listening conditions around the SRT. At more favorable SNRs (SRT + 3 dB), this benefit was lost. We hypothesize that TNRmb was beneficial at lower SNRs, because of more effective artifact detection under those conditions. Group-averaged settings of the multiband algorithm did not significantly affect speech recognition. TNRbb decreased speech recognition significantly using personalized parameter settings. Rating scores were not significantly affected by the algorithms under any condition tested. The currently available TNR algorithm for Advanced Bionics systems (SoundRelax) is a broadband filter that does not support personalization of its settings. Future iterations of this algorithm might benefit from upgrading it to a multiband variant with the option to personalize its parameter settings.

Using Microphone Technology to Improve Speech Perception in Noise in Children with Cochlear Implants.

Cochlear implant (CI) users are affected more than their normal hearing (NH) peers by the negative consequences of background noise on speech understanding. Research has shown that adult CI users can improve their speech recognition in challenging listening environments by using dual-microphone beamformers, such as adaptive directional microphones (ADMs) and wireless remote microphones (RMs). The suitability of these microphone technologies for use in children with CIs is not well-understood nor widely accepted. To assess the benefit of ADM or RM technology on speech perception in background noise in children and adolescents with cochlear implants (CIs) with no previous or current use of ADM or RM. Mixed, repeated measures design. Twenty (20) children, ten (10) CI users (mean age 14.3 yrs) who used Advanced Bionics HiRes90K implants with research Naida processors, and ten (10) NH age-matched controls participated in this prospective study. CI users listened with an ear-canal level microphone, T-Mic (TM), an ADM, and a wireless RM at different audio-mixing ratios. Speech understanding with five microphone settings (TM 100%, ADM, RM + TM 50/50, RM + TM 75/25, RM 100%) was evaluated in quiet and in noise. Speech perception ability was measured using children's spondee words to obtain a speech recognition threshold for 80% accuracy (SRT80%) in 20-talker babble where the listener sat in a sound booth 1 m (3.28') from the target speech (front) and noise (behind) to test five microphone settings (TM 100%, ADM, RM + TM 50/50, RM + TM 75/25, RM 100%). Group performance-intensity functions were computed for each listening condition to show the effects of microphone configuration with respect to signal-to-noise ratio (SNR). A difference score (CI Group minus NH Group) was computed to show the effect of microphone technology at different SNRs relative to NH. Statistical analysis using a repeated-measures analysis of variance evaluated the effects of the microphone configurations on SRT80% and performance at SNRs. Between-groups analysis of variance was used to compare the CI group with the NH group. The speech recognition was significantly poorer for children with CI than children with NH in quiet and in noise when using the TM alone. Adding the ADM or RM provided a significant improvement in speech recognition for the CI group over use of the TM alone in noise (mean dB advantage ranged from 5.8 for ADM to 16 for RM100). When children with CI used the RM75 or RM100 in background babble, speech recognition was not statistically different from the group with NH. Speech recognition in noise performance improved with the use of ADM and RM100 or RM75 over TM-only for children with CIs. Alhough children with CI remain at a disadvantage as compared with NH children in quiet and more favorable SNRs, microphone technology can enhance performance for some children with CI to match that of NH peers in contexts with negative SNRs.

Benefit of binaural listening as revealed by speech intelligibility and listening effort.

In contrast to the well-known benefits for speech intelligibility, the advantage afforded by binaural stimulus presentation for reducing listening effort has not been thoroughly examined. This study investigated spatial release of listening effort and its relation to binaural speech intelligibility in listeners with normal hearing. Psychometric functions for speech intelligibility of a frontal target talker masked by a stationary speech-shaped noise were estimated for several different noise azimuths, different degrees of reverberation, and by maintaining only interaural level or time differences. For each of these conditions, listening effort was measured using a categorical scaling procedure. The results revealed that listening effort was significantly reduced when target and masker were spatially separated in anechoic conditions. This effect extended well into the range of signal-to-noise ratios (SNRs) in which speech intelligibility was at ceiling, and disappeared only at the highest SNRs. In reverberant conditions, spatial release from listening effort was observed for high, but not low, direct-to-reverberant ratios. The findings suggest that listening effort assessment can be a useful method for revealing the benefits of spatial separation of sources under realistic listening conditions comprising favorable SNRs and low reverberation, which typically are not apparent by other means.

Noise and pitch interact during the cortical segregation of concurrent speech

Behavioral studies reveal listeners exploit intrinsic differences in voice fundamental frequency (F0) to segregate concurrent speech sounds—the so-called “F0-benefit.” More favorable signal-to-noise ratio (SNR) in the environment, an extrinsic acoustic factor, similarly benefits the parsing of simultaneous speech. Here, we examined the neurobiological substrates of these two cues in the perceptual segregation of concurrent speech mixtures. We recorded event-related brain potentials (ERPs) while listeners performed a speeded double-vowel identification task. Listeners heard two concurrent vowels whose F0 differed by zero or four semitones presented in either clean (no noise) or noise-degraded (+5 dB SNR) conditions. Behaviorally, listeners were more accurate in correctly identifying both vowels for larger F0 separations but F0-benefit was more pronounced at more favorable SNRs (i.e., pitch × SNR interaction). Analysis of the ERPs revealed that only the P2 wave (∼200 ms) showed a similar F0 x SNR interaction as behavior and was correlated with listeners' perceptual F0-benefit. Neural classifiers applied to the ERPs further suggested that speech sounds are segregated neurally within 200 ms based on SNR whereas segregation based on pitch occurs later in time (400–700 ms). The earlier timing of extrinsic SNR compared to intrinsic F0-based segregation implies that the cortical extraction of speech from noise is more efficient than differentiating speech based on pitch cues alone, which may recruit additional cortical processes. Findings indicate that noise and pitch differences interact relatively early in cerebral cortex and that the brain arrives at the identities of concurrent speech mixtures as early as ∼200 ms.

Speech intelligibility and spatial release from masking in maskers with different spectro-temporal modulations

Speech-reception thresholds (SRTs) decrease as target and maskers are spatially separated (spatial release from masking, SRM) even if two maskers are symmetrically placed around the listener's head. In this case, speech intelligibility (SI) cannot be explained by an improved long-term signal-to-noise-ratio (SNR) caused by the head shadow at one better ear alone, but could be facilitated by short-term spectro-temporal segments (“glimpses”) in each ear that provide favorable SNRs. Here it was systematically assessed how SRT and SRM depend on the spectro-temporal masker properties and on the availability of specific binaural cues for a frontal target in a symmetric masker setup. Maskers ranged from stationary noise to single, interfering talkers. Maskers were modified by head-related transfer functions providing different binaural cues (interaural level and time differences; ILD, ITD, both), by presenting only glimpses derived with a fast-switching better-ear mechanism, and an “infinite ILD,” removing crosstalk of the maskers between the ears. Results were compared to model predictions showing that spectral cues contribute to SRM for all maskers, while IPD and ILD cues were more important for modulated maskers. The “infinite ILD” condition suggests binaural processing limitations, resulting in a maximal SRM of 12 dB for low or absent informational masking.

Exploiting Polarimetric TerraSAR-X Data for Sea Clutter Characterization

This paper presents a detailed characterization of sea/ocean clutter returns at X-band, imaged by TerraSAR-X (TSX) mission from the radiometric, statistical, and polarimetric standpoints. Different TSX data takes, covering the typical spaceborne incidence angle region (20°–45°), are analyzed: dual-polarized (dual-pol) and experimental quad-polarized (quad-pol) data have been used. The thermal noise of the receiver for quad-pol data turns out to be an important limitation in the sea characterization from TSX, particularly at high incidence angles (above 36°), where low signal-to-noise ratios (SNRs) can impair the proper data distribution fitting and the polarimetric backscattering description. Statistical analysis shows large deviation from Gaussianity, indicating presence of texture, mainly in the small incidence region (20°–36°), with favorable SNR conditions. The different polarimetric features revealed contribution of nonpolarized scattering, related to the presence of breaking waves. This paper also proposes and evaluates an extension of the well-known X-Bragg model, named X2-Bragg (extended-extended Bragg), which properly accounts for the impact of thermal noise and sea clutter temporal decorrelation, due to the dual receive antenna (DRA) acquisition mode. Such additional decorrelation sources, if not properly analyzed and accounted for in the physical-based model description, could lead to an incorrect interpretation of the polarimetric properties and the related erroneous geophysical parametric inversion from the real data. In this sense, the X2-Bragg proves its fitting to the experimental data, quantifying accordingly the presence of nonpolarized scattering in terms of the roughness parameter $\beta_{1}$ .

Directional Benefit Is Present with Audiovisual Stimuli: Limiting Ceiling Effects

Past research demonstrates that as the speech recognition performance of listeners fitted with omnidirectional hearing aids approaches maximum (ceiling), the benefit afforded by directional microphones is necessarily lessened. This effect could potentially eliminate the benefit provided by directional microphones in easier listening situations, such as environments with visual cues and favorable signal-to-noise ratios (SNRs). The purpose of this study was to evaluate directional benefit using auditory-visual stimuli in SNRs commonly found in the real world (ranging from +3 to +12 dB). In order to maximize the possibility of directional benefit, a bilateral beamformer was used, which functions as a highly directional microphone. Sentence recognition was evaluated in three SNRs and in two levels of reverberation (low and moderate). For each SNR and reverberation combination, sentence recognition was evaluated using omnidirectional and bilateral beamformer microphone modes. A total of 15 adults with hearing loss participated. Only listeners who had significant difficulty understanding speech in noise were included. Sentence recognition scores were evaluated using analysis of variance with three within-participant variables (SNR, reverb, microphone mode). Follow-up analyses were conducted using linear contrast while controlling for family-wise error rate. RESULTS revealed significant bilateral beamformer benefit ranging from approximately 22-30 rationalized arcsine units (∼20-28 percentage points) in both low and moderate reverberation across all tested SNRs (+3 to +12 dB). These results provide support for the use of bilateral beamformers, even at relatively favorable SNRs and in the presence of visual cues, for listeners who demonstrate poor sentence recognition in noise.

Assessing listening effort by measuring short-term memory storage and processing of speech in noise

ObjectiveThe aim of this study was to investigate the effect of working memory capacity (WMC) and updating ability (UA) on listening effort measured using a new test, the Auditory Inference Span Test (AIST), as an objective measure of listening effort.DesignThe AIST is based on Swedish five-word sentences and taps into three memory load levels (MLLs). It was administered in stationary speech-shaped noise at −2, −4, and −6 dB signal-to-noise ratio (SNR). WMC was assessed using the reading span test, and UA was assessed using the letter memory test. We also collected data on speech-in-noise performance and subjectively rated listening effort at the three SNRs.Study sampleThirty-nine participants with normal hearing thresholds (≤20 dB HL for 250 to 4000 Hz) took part in the study.ResultsAIST performance decreased with increasing MLL and was related to WMC and UA. Participants with high WMC performed better than those with low WMC at more favorable SNRs. Participants with high UA performed better than participants with low UA at the intermediate MLL, which made particular demands on the UA. Neither speech recognition scores nor subjectively rated listening effort was associated with AIST performance or either of the cognitive variables.ConclusionAIST taps into cognitive functions necessary for understanding speech in noise. However, in its current form AIST may be too cognitively taxing to successfully measure graded listening effort in participants with lower cognitive capacity.

Effects of Noise Reduction on AM and FM Perception

The goal of noise reduction (NR) algorithms in digital hearing aid devices is to reduce background noise whilst preserving as much of the original signal as possible. These algorithms may increase the signal-to-noise ratio (SNR) in an ideal case, but they generally fail to improve speech intelligibility. However, due to the complex nature of speech, it is difficult to disentangle the numerous low- and high-level effects of NR that may underlie the lack of speech perception benefits. The goal of this study was to better understand why NR algorithms do not improve speech intelligibility by investigating the effects of NR on the ability to discriminate two basic acoustic features, namely amplitude modulation (AM) and frequency modulation (FM) cues, known to be crucial for speech identification in quiet and in noise. Here, discrimination of complex, non-linguistic AM and FM patterns was measured for normal hearing listeners using a same/different task. The stimuli were generated by modulating 1-kHz pure tones by either a two-component AM or FM modulator with patterns changed by manipulating component phases. Modulation rates were centered on 3 Hz. Discrimination of AM and FM patterns was measured in quiet and in the presence of a white noise that had been passed through a gammatone filter centered on 1 kHz. The noise was presented at SNRs ranging from -6 to +12 dB. Stimuli were left as such or processed via an NR algorithm based on the spectral subtraction method. NR was found to yield small but systematic improvements in discrimination for the AM conditions at favorable SNRs but had little effect, if any, on FM discrimination. A computational model of early auditory processing was developed to quantify the fidelity of AM and FM transmission. The model captured the improvement in discrimination performance for AM stimuli at high SNRs with NR. However, the model also predicted a relatively small detrimental effect of NR for FM stimuli in contrast with the average psychophysical data. Overall, these results suggest that the lack of benefits of NR on speech intelligibility is partly caused by the limited effect of NR on the transmission of narrowband speech modulation cues.

Effects of frequency compression on the intelligibility and quality of speech in noise.

Frequency-lowering technologies such as frequency compression have become common in high-end digital hearing aids. However, there are few data on the consequences of adjusting frequency compression ratio (FCR) and frequency compression cutoff (FCC). In this study, sentences at signal-to-noise ratios (SNRs) ranging from −10 to +10 dB were frequency compressed at a variety of FCRs (1.5–3) and FCCs (1–2 kHz). Frequency compression was implemented using sinusoidal modeling: the incoming signal was segmented, the spectral peaks found for each segment, and an output sinusoid at a shifted frequency was generated for each peak. Subjects were adult listeners with normal hearing or mild-moderate sensorineural loss. Intelligibility results illustrate a complex interaction between SNR and frequency compression parameters. At favorable SNRs, frequency compression had minimal effects. At less favorable SNRs, reducing FCC degraded intelligibility more than reducing FCR. At the poorest SNRs any amount of frequency compression degraded intelligibility but the specific FCC/FCR had little effect. Quality results show less interaction whereby any frequency compression was perceived as reducing speech quality. Compared to data from normal-hearing listeners, results from listeners with hearing loss were more variable and were interpretable in the context of audiogram configuration. [Work supported by NIH and GN ReSound.]

Auditory and auditory-visual intelligibility of speech in fluctuating maskers for normal-hearing and hearing-impaired listeners

Speech intelligibility for audio-alone and audiovisual (AV) sentences was estimated as a function of signal-to-noise ratio (SNR) for a female target talker presented in a stationary noise, an interfering male talker, or a speech-modulated noise background, for eight hearing-impaired (HI) and five normal-hearing (NH) listeners. At the 50% keywords-correct performance level, HI listeners showed 7-12 dB less fluctuating-masker benefit (FMB) than NH listeners, consistent with previous results. Both groups showed significantly more FMB under AV than audio-alone conditions. When compared at the same stationary-noise SNR, FMB differences between listener groups and modalities were substantially smaller, suggesting that most of the FMB differences at the 50% performance level may reflect a SNR dependence of the FMB. Still, 1-5 dB of the FMB difference between listener groups remained, indicating a possible role for reduced audibility, limited spectral or temporal resolution, or an inability to use auditory source-segregation cues, in directly limiting the ability to listen in the dips of a fluctuating masker. A modified version of the extended speech-intelligibility index that predicts a larger FMB at less favorable SNRs accounted for most of the FMB differences between listener groups and modalities. Overall, these data suggest that HI listeners retain more of an ability to listen in the dips of a fluctuating masker than previously thought. Instead, the fluctuating-masker difficulties exhibited by HI listeners may derive from the reduced FMB associated with the more favorable SNRs they require to identify a reasonable proportion of the target speech.

Effects of speechreading and signal-to-noise ratio on understanding mainstream American English by American and Indian adults.

The purpose of this study was to measure effects of speechreading and signal‐to‐noise ratio (SNR) on understanding mainstream American English (MAE) heard by 30 Indian adults compared to 30 American adults. Participants listened to a recording of a female speaker of MAE saying ten lists of ten different everyday speech sentences per list. Participants heard sentences from a TV loudspeaker at a 65 dB sound pressure level, while a four‐talker babble played through two surrounding loudspeakers at various SNRs under auditory‐visual and auditory modalities. Each participant’s speechreading performance at each SNR was computed as the difference in words correctly heard through auditory‐visual versus auditory modalities. Consistent with most previous research, American participants benefited significantly more from speechreading at poorer SNRs than at favorable SNRs. The novel finding of this study, however, was that Indian participants benefited less from speechreading than American participants at poorer SNRs, but benefited more from speechreading than American participants at favorable SNRs. Linguistic (and, possibly, nonlinguistic) variables may have accounted for these findings, including an increased need for Indian participants to integrate more auditory cues with visual cues to benefit from speechreading, presumably because they only spoke English as a second language.

Audition and Cognition: Where Lab Meets Clinic

Audition and Cognition: Where Lab Meets Clinic

Intervention for a Child with Auditory Neuropathy/Dys-synchrony

Intervention for a Child with Auditory Neuropathy/Dys-synchrony

Directional hearing AIDS.

Directional hearing AIDS.

Children's perception of speech in multitalker babble.

Children 5, 9, and 11 years of age and young adults attempted to identify the final word of sentences recorded by a female speaker. The sentences were presented in two levels of multitalker babble, and participants responded by selecting one of four pictures. In a low-noise condition, the signal-to-noise ratio (SNR) was adjusted for each age group to yield 85% correct performance. In a high-noise condition, the SNR was set 7 dB lower than the low-noise condition. Although children required more favorable SNRs than adults to achieve comparable performance in low noise, an equivalent decrease in SNR had comparable consequences for all age groups. Thus age-related differences on this task can be attributed primarily to sensory factors.

Identification of neonatal hearing impairment: distortion product otoacoustic emissions during the perinatal period.

1) To describe distortion product otoacoustic emission (DPOAE) levels, noise levels and signal to noise ratios (SNRs) for a wide range of frequencies and two stimulus levels in neonates and infants. 2) To describe the relations between these DPOAE measurements and age, test environment, baby state, and test time. DPOAEs were measured in 2348 well babies without risk indicators, 353 well babies with at least one risk indicator, and 4478 graduates of neonatal intensive care units (NICUs). DPOAE and noise levels were measured at f2 frequencies of 1.0, 1.5, 2.0, 3.0, and 4.0 kHz, and for primary levels (L1/L2) of 65/50 dB SPL and 75/75 dB SPL. Measurement-based stopping rules were used such that a test did not terminate unless the response was at least 3 dB above the mean noise floor + 2 SDs (SNR) for at least four of five test frequencies. The test would terminate, however, if these criteria were not met after 360 sec. Baby state, test environment, and other test factors were captured at the time of each test. DPOAE levels, noise levels and SNRs were similar for well babies without risk indicators, well babies with risk indicators, and NICU graduates. There was a tendency for larger responses at f2 frequencies of 1.5 and 2.0 Hz, compared with 3.0 and 4.0 kHz; however, the noise levels systematically decreased as frequency increased, resulting in the most favorable SNRs at 3.0 and 4.0 kHz. Response levels were least and noise levels highest for an f2 frequency of 1.0 kHz. In addition, test time to achieve automatic stopping criteria was greatest for 1.0 kHz. With the exception of "active/alert" and "crying" babies, baby state had little influence on DPOAE measurements. Additionally, test environment had little impact on these measurements, at least for the environments in which babies were tested in this study. However, the lowest SNRs were observed for infants who were tested in functioning isolettes. Finally, there were some subtle age affects on DPOAE levels, with the infants born most prematurely producing the smallest responses, regardless of age at the time of test. DPOAE measurements in neonates and infants result in robust responses in the vast majority of ears for f2 frequencies of at least 2.0, 3.0 and 4.0 kHz. SNRs decrease as frequency decreases, making the measurements less reliable at 1.0 kHz. When considered along with test time, there may be little justification for including an f2 frequency at 1.0 kHz in newborn screening programs. It would appear that DPOAEs result in reliable measurements when tests are conducted in the environments in which babies typically are found. Finally, these data suggest that babies can be tested in those states of arousal that are most commonly encountered in the perinatal period.