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Cochlear mechanisms and processes
Published in Stanley A. Gelfand, Hearing, 2017
The cochlear microphonic is a graded potential, which means that its magnitude changes as the stimulus level is raised or lowered. This is shown by the input–output (I-O) function of the cochlear microphonic. Figure 4.15 shows an idealized example of a cochlear microphonic I-O function abstracted from several classical sources. Notice that the magnitude of the cochlear microphonic increases linearly over a stimulus range of roughly 60 dB, as shown by the straight line segment of the I-O function (e.g., Wever and Lawrence, 1950, 1954). The hypothetical function in the figure shows the linear response extending down to about 0.4 μV, but CM magnitudes have actually been recorded as small as a few thousandths of a microvolt (Wever, 1966). Saturation occurs as the stimulus level is raised beyond the linear segment of the I-O function, as shown by the flattening of the curve. Increasing amounts of harmonic distortion occur in this region. Raising the intensity of the stimulus even further causes overloading, in which case the overall magnitude of the CM can actually decrease.
Otology
Published in Adnan Darr, Karan Jolly, Jameel Muzaffar, ENT Vivas, 2023
Jameel Muzaffar, Chloe Swords, Adnan Darr, Karan Jolly, Manohar Bance, Sanjiv Bhimrao
Key concepts: Benefit noticed when >30 dB loss over three frequencies (three subthreshold levels required for programming)Acoustic gain: Amount of amplification provided by hearing aid, difference between input and output SPL (50 dB tone presented vs output of 80 dB = 30 dB gain)High frequency average “HFA” gain: Average gain at 1000, 1600 and 2500 HzHarmonic distortion: Addition of frequencies not present in original soundSaturation sound pressure: Max sound pressure the aid can produceDynamic range: Amount of amplification before sound becomes uncomfortableOcclusion effect: Perception of loudness of own voice as bone conducted sound is trapped by occlusive objectMore common if normal hearing at low frequencies and poor hearing at high frequencies (occlusion effect at <500 Hz)Managed by ear mould modifications (used less now due to advances in technology but still useful particularly in children) Non-occluding or open ear mould reduces low-frequency energyTreated by increasing venting: Hole in mould from EAC to the outside to reduce pressure sensation e.g. Libby Horn, “reverse horn”ACHAs are readily available and inexpensive Occlusive mould (50 dB or worse) i.e. moderate to severe HL Limit feedbackReduce loss of amplified soundReduced ventilation, hence predispose to infections, modify with widened vents, hypoallergenic or softer mouldsDome (open fit for 30–50 dB) i.e. mild-to-moderate HL
Calibration and initial validation of a low-cost computer-based screening audiometer coupled to consumer insert phone-earmuff combination for boothless audiometry
Published in International Journal of Audiology, 2022
Kumar Seluakumaran, Majdina N. Shaharudin
Floor noise was measured in 1/3 octave bands when the IP was connected to the sound card and laptop running the LabVIEW program, with the signal amplitude set at zero voltage. Input/output accuracy was assessed based on the deviation of the measured signal frequency peak and its level from the target specified in the LabVIEW interface. As cheaper earphones often produce unwanted distortions at higher output levels, the total harmonic distortion or THD (ratio of the power of the harmonic distortions to the power of the signal frequency) was also measured using the Spectra PLUS software. Both signal accuracy and TDH were determined at five test frequencies (0.5, 1, 2, 4, and 8 kHz) with the SGIP output set at 80 dB SPL. Attenuation linearity was checked in 5-dB steps from 80 dB SPL to the lowest measurable levels for all test frequencies to verify if a 5-dB decrease in the amplitude dial of the LabVIEW’s interface also led to 5-dB drop in the measured SGIP output levels. Finally, the output from the left and right earpieces of SGIP were compared to ascertain if a single set of calibration values can be applied to both channels.
Presence of ipsilateral acoustic reflex artifact may result in clinical misidentification
Published in International Journal of Audiology, 2022
Dorothy Neave-DiToro, Michael Bergen, Shlomo Silman, Michele B. Emmer
It is feasible that a distortion is being created in the calibration cavity when the probe tone and second stimulus at 0.5 kHz, 1 kHz, and 2 kHz are presented simultaneously. The question arises as to type and cause of the distortion? Are we dealing with intermodulation distortion, harmonic distortion, or simply amplitude distortion. It is possible to rule out both intermodulation and harmonic distortion as these would occur at a frequency other than 0.226 kHz. Whether such a distortion is registered would depend on how wide the input pass-band is on the specific system. However, an amplitude distortion would occur exactly at 0.226 kHz and would easily be recorded and visible. The cause of this distortion can simply be a nonlinerity or an overload type of distortion caused by the simultaneous presentation of the stimulus and probe tone. Another possibility is cross talk. If the path of the stimulus tone and the path of the probe tone are not properly isolated in the electrical circuit, the level of the probe tone may be increased by providing additional voltage to that part of the circuit when the stimulus tone is activated.
An evaluation of the Sennheiser HDA 280-CL circumaural headphone for use in audiometric testing
Published in International Journal of Audiology, 2019
Paula Folkeard, Marianne Hawkins, Susan Scollie, Bilal Sheikh, Vijay Parsa
Total harmonic distortion (THD) was measured using the same ear simulator set up described in the ETSPL section. The median ETSPL from study 1 was used to determine the initial starting sound pressure level for 70 dB HL for each frequency from 125 to 10,000 Hz in accordance to IEC 60645–1 (2017). The level was increased in 5 dB steps and measurements were made for presentation levels up to 75 dB HL for 125 Hz, 90 dB HL for 250 Hz and 110 dB HL 500–10,000 Hz. The THD for each test frequency was calculated using the values obtained from the SpectraPlus spectrum analysis system using narrowband Fast Fourier Transform (FFT).