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Haas EffectAlso called the precedence effect. If similar sounds arrive at the ear within approximately 35 ms, the apparent direction of the sound is that of the direct sound. The auditory apparatus integrates delayed sounds if they fall on the ear within 20 to 40 ms of the direct sound. The level of the delayed components contributes to the apparent level of the sound, and may be accompanied by a pleasant change in the character of the sound. See Fusion Zone.
Hair CellThe sensory elements of the cochlea that transduce the mechanical vibrations of the basilar membrane to nerve impulses that are sent to the brain.
Hamming WindowNamed after its originator, the Hamming window is a Hanning window sitting on top of a small rectangular pedestal. Its function is similar to the Hanning window, but has its first side lobes 42 dB down, whereas the Hanning window’s first side lobes are only 32 dB down. Thus, the Hamming window has better selectivity for large signals, but it suffers from the disadvantage that the rest of the side lobes are higher, and in fact fall off slowly at 20 dB per octave like those of the rectangular window. The Hamming window had some advantage in the days when FFT analyzers only had 50 dB or so of dynamic range, but nowadays it is essentially obsolete.
Hand-arm Co-ordinate SystemThe axes of the co-ordinate system are mutually perpendicular. The origin of the co-ordinate system is in the centre of the root joint of the middle finger.
Hand-arm VibrationThis is a quantitative measure of the effect of vibration on the human arm, for example, when using power tools over a prolonged period of time. The main application areas are hand-held construction machinery (pneumatic and electrically powered tools, chain saws, etc.) and the automotive industry (motorcycles, mopeds, etc.).
Hanning WindowA smooth amplitude weighting of the time signal that is zero at the beginning and the end of the time record. Used with gated continuous signals and long transients to give them a slow onset and cut-off in order to reduce the generation of side lobes in their frequency spectrum. The selectivity of the Hanning window is good, and the maximum picket-fence-error is 1.42 dB.
HarmonicA discrete sinusoidal (pure-tone) component whose frequency is an integer multiple of the fundamental frequency of the wave. If a component has a frequency twice that of the fundamental, it is called the second harmonic, etc.
Harmonic ResponseIn a situation where the (stationary) process forces in a structure are cyclical (which is typical for the free forces and moments from rotating machinery), the vibration spectrum, when measuring the response at an arbitrary position on the structure, is usually characterised by one or more predominant lines. Such a response spectrum is known as harmonic response.
Harmonic SeriesComponents of a spectrum that are integer multiples of the fundamental frequency. A harmonic series in a spectrum is the result of a periodic signal in the waveform. Harmonic series are very common in spectra of machinery vibration.
HATSHead and torso simulator used for sound quality and telecom measurements.
Due to the direction-dependent scattering caused by a torso, head and pinnae, sounds reaching the ears of a listener are essentially different. The scattering can be determined by measuring head-related transfer functions, which represent the filtering of sounds from a free field to a measurement point at the ears of the listener.
HeadphonesAn assembly comprising two earphones and a headband or equivalent device to hold these in place with a chosen force.
HeadroomThe amount of room between the normal operating level and the maximum level where clipping (distortion) occurs. This number tells you how much louder a signal can get before distortion
Hearing LevelA measured threshold of hearing at a specified frequency expressed in decibels relative to a specified standard of normal hearing. The deviation in decibels of an individual’s threshold from the zero reference of an audiometer.
Hearing LossA term denoting an impairment of auditory acuity. The amount of hearing impairment, in decibels, measured as a set of hearing threshold levels at specified frequencies. Types of hearing loss are: 1. Conductive: A loss originating in the conductive mechanism of the ear; 2. Sensor-neural: A loss originating in the cochlea or the fibres of the auditory nerve; 3. Noise induced: A sensor-neural loss attributed to the effects of noise. Measured in dB below a standard level. Hearing loss can be related to disease, injury, age or exposure to high-level sound.
Hearing ProtectorA general term embracing earmuff, earplug, and helmet (or other noise excluding device) worn on the head.
Hearing Threshold Level (HTL)A measured threshold of hearing, expressed in decibels relative to a specified audiometric zero. The amount by which an individual’s threshold of audibility differs from a standard audiometric threshold.
Helmholtz ResonatorA reactive, tuned, sound absorber. A bottle is such a resonator. Helmholtz resonators can employ a perforated cover or slats over a cavity.
HenryThe unit of inductance.
Hertz (Hz)The unit of frequency, abbreviated as Hz. One hertz is equal to one cycle per second. The name is in honour of Heinrich Hertz, an early German investigator of radio wave transmission. See also Frequency.
High-Pass FilterA filter that passes signal frequencies above a specific, or cut-off, frequency but attenuates low-frequency components. They are used in instrumentation to eliminate low-frequency noise, and to separate alternating components from direct (DC) components in a signal.
Hilbert TransformA mathematical transform that changes real-valued time functions (correlation functions, impulse response functions, etc.) into complex-values time functions whose imaginary part is the Hilbert Transform of the original real-valued time domain signal. The complex-valued time domain functions are called analytic signals and can be displayed in terms of magnitude and phase versus time. The magnitude of the analytic signal describes the envelope of the original signal and the phase leads to an “instantaneous frequency” for signals sweeping in frequency with time.
HysteresisNon-uniqueness in the relationship between two variables as a parameter increases or decreases. Also called dead-band, or the portion of the system’s response where a change in input does not produce a change in output.
Hysteresis Damping(Hysteretic Damping, Structural Damping). Energy losses within a structure that are caused by internal friction within the structure. These losses are independent of speed or frequency of oscillation but are proportional to the vibration amplitude squared.
Hysteresis ValueLagging effect. Specifies a minimum percentage change in a tacho signal relative to the maximum input for the tacho channel that must occur after the slope and level conditions have been met for identification and triggering of a tacho pulse.Brüel & Kjær Sound & Vibration Dictionary End User Agreement