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Weighting filter
A weighting filter is used to emphasize or suppress some aspects of a phenomenon compared to others, for measurement or other purposes.
In each field of audio measurement, special units are used to indicate a weighted measurement as opposed to a basic physical measurement of energy level. For sound, the unit is the phon (1 kHz equivalent level).
Sound has three basic components, the wavelength, frequency, and speed. In sound measurement, we measure the loudness of the sound in decibels (dB). Decibels are logarithmic with 0 dB as the reference. There are also a range of frequencies that sounds can have. Frequency is the number of times a sine wave repeats itself in a second. Normal auditory systems can usually hear between 20 and 20,000 Hz. When we measure sound, the measurement instrument takes the incoming auditory signal and analyzes it for these different features. Weighting filters in these instruments then filter out certain frequencies and decibel levels depending on the filter. A weighted filters are most similar to natural human hearing. This allows the sound level meter to determine what decibel level the incoming sound would likely be for a normal hearing human's auditory system.
In the measurement of loudness, for example, an A-weighting filter is commonly used to emphasize frequencies around 3–6 kHz where the human ear is most sensitive, while attenuating very high and very low frequencies to which the ear is insensitive. The aim is to ensure that measured loudness corresponds well with subjectively perceived loudness. A-weighting is only really valid for relatively quiet sounds and for pure tones as it is based on the 40-phon Fletcher–Munson equal-loudness contour. The B and C curves were intended for louder sounds (though they are less used) while the D curve is used in assessing loud aircraft noise (IEC 537). B curves filter out more medium loudness levels when compared to an A curves. This curve is rarely ever used in the assessment or monitoring of noise levels anymore. C curves differ from both A and B in the fact that they filter less of the lower and higher frequencies. The filter is a much flatter shape and is used in sound measurement in especially loud and noisy environments. A weighted curves follow a 40 phon curve while C weighted follows a 100 phon curve. The three curves differ not in their measurement of exposure levels, but in the frequencies measured. A weighted curves allow more frequencies equal to or less than 500 Hz through, which is most representative of the human ear.
There are a variety of reasons for measuring sound. This includes following regulations to protect worker's hearing, following noise ordinances, in telecommunications, and many more. At the basis of sound measurement is the idea of breaking down an incoming signal based on its different properties. Every incoming sinusoidal wave of sound has a frequency and amplitude. Using this information, a sound level can be deduced from the root-sums-of-squares of the amplitudes of all the incoming auditory information. Whether using a sound level meter or a noise dosimeter, the processing is somewhat similar. With a calibrated sound level meter, the incoming sounds are going to be picked up by the microphone and then measured by the internal electronic circuits. The sound measurement that the device outputs can be filtered through an A, B, or C weighting curve. The curve used will have slight effects on the resulting decibel level.
In the field of telecommunications, weighting filters are widely used in the measurement of electrical noise on telephone circuits, and in the assessment of noise as perceived through the acoustic response of different types of instrument (handset). Other noise-weighting curves have existed, e.g. DIN standards. The term psophometric weighting, though referring in principle to any weighting curve intended for noise measurement, is often used to refer to a particular weighting curve, used in telephony for narrow-bandwidth voiceband speech circuits.
A-weighted decibels are abbreviated dB(A) or dBA. When acoustic (calibrated microphone) measurements are being referred to, then the units used will be dB SPL (sound pressure level) referenced to 20 micropascals = 0 dB SPL.
The A-weighting curve has been widely adopted for environmental noise measurement, and is standard in many sound level meters (see ITU-R 468 weighting for a further explanation).
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Weighting filter
A weighting filter is used to emphasize or suppress some aspects of a phenomenon compared to others, for measurement or other purposes.
In each field of audio measurement, special units are used to indicate a weighted measurement as opposed to a basic physical measurement of energy level. For sound, the unit is the phon (1 kHz equivalent level).
Sound has three basic components, the wavelength, frequency, and speed. In sound measurement, we measure the loudness of the sound in decibels (dB). Decibels are logarithmic with 0 dB as the reference. There are also a range of frequencies that sounds can have. Frequency is the number of times a sine wave repeats itself in a second. Normal auditory systems can usually hear between 20 and 20,000 Hz. When we measure sound, the measurement instrument takes the incoming auditory signal and analyzes it for these different features. Weighting filters in these instruments then filter out certain frequencies and decibel levels depending on the filter. A weighted filters are most similar to natural human hearing. This allows the sound level meter to determine what decibel level the incoming sound would likely be for a normal hearing human's auditory system.
In the measurement of loudness, for example, an A-weighting filter is commonly used to emphasize frequencies around 3–6 kHz where the human ear is most sensitive, while attenuating very high and very low frequencies to which the ear is insensitive. The aim is to ensure that measured loudness corresponds well with subjectively perceived loudness. A-weighting is only really valid for relatively quiet sounds and for pure tones as it is based on the 40-phon Fletcher–Munson equal-loudness contour. The B and C curves were intended for louder sounds (though they are less used) while the D curve is used in assessing loud aircraft noise (IEC 537). B curves filter out more medium loudness levels when compared to an A curves. This curve is rarely ever used in the assessment or monitoring of noise levels anymore. C curves differ from both A and B in the fact that they filter less of the lower and higher frequencies. The filter is a much flatter shape and is used in sound measurement in especially loud and noisy environments. A weighted curves follow a 40 phon curve while C weighted follows a 100 phon curve. The three curves differ not in their measurement of exposure levels, but in the frequencies measured. A weighted curves allow more frequencies equal to or less than 500 Hz through, which is most representative of the human ear.
There are a variety of reasons for measuring sound. This includes following regulations to protect worker's hearing, following noise ordinances, in telecommunications, and many more. At the basis of sound measurement is the idea of breaking down an incoming signal based on its different properties. Every incoming sinusoidal wave of sound has a frequency and amplitude. Using this information, a sound level can be deduced from the root-sums-of-squares of the amplitudes of all the incoming auditory information. Whether using a sound level meter or a noise dosimeter, the processing is somewhat similar. With a calibrated sound level meter, the incoming sounds are going to be picked up by the microphone and then measured by the internal electronic circuits. The sound measurement that the device outputs can be filtered through an A, B, or C weighting curve. The curve used will have slight effects on the resulting decibel level.
In the field of telecommunications, weighting filters are widely used in the measurement of electrical noise on telephone circuits, and in the assessment of noise as perceived through the acoustic response of different types of instrument (handset). Other noise-weighting curves have existed, e.g. DIN standards. The term psophometric weighting, though referring in principle to any weighting curve intended for noise measurement, is often used to refer to a particular weighting curve, used in telephony for narrow-bandwidth voiceband speech circuits.
A-weighted decibels are abbreviated dB(A) or dBA. When acoustic (calibrated microphone) measurements are being referred to, then the units used will be dB SPL (sound pressure level) referenced to 20 micropascals = 0 dB SPL.
The A-weighting curve has been widely adopted for environmental noise measurement, and is standard in many sound level meters (see ITU-R 468 weighting for a further explanation).