T10 the time within a single noise event where the level is below 10 dB of the maximum level. Also known as the 10 dB-downtime during an aircraft fly-by
Third Octave Band octave bands sub-divided into three parts, equal to 23% of the centre frequency. Used when octave analysis is not discrete enough. Divides the audio spectrum into 33 or more equal parts with constant percentage bandwidth filter.
The cut-off frequencies have a ratio of 21/3, which is approximately 1.26. For example a 1 kHz third-octave band filter has a centre frequency of 1000 Hz with lower and upper frequencies of 891 Hz and 1112 Hz respectively
Third Octave Filter alternative name for third octave band. Which is preferably centred at one of the preferred frequencies in ISO R266. Should meet the attenuation characteristics of IEC R266, IEC R255 and ANSI S1.11-1966 Class III.
Masked Threshold threshold of audibility for a specified sound in the presence of another (masking) sound
See also • auditory masking
Threshold of Pain the threshold of pain, being subjective, varies in the literature from 120 dBA to 140 dBA. However 120 dBA is most common.
Threshold Shift a change in the threshold of audibility at a specified frequency from a threshold previously established. The amount of threshold shift is expressed in decibels.
It is usually assumed that the following components are additive, at least for small values of the components.
Age Related Threshold Shift (ARTS) is the component of permanent threshold shift related to age.
Noise Induced Permanent Threshold Shift (NIPTS) is the component of permanent threshold shift associated with a noise exposure.
Permanent Threshold Shift (PTS) the component of threshold shift that shows no progressive recovery with the passage of time when the apparent cause has been removed.
Temporary Threshold Shift (TTS) an upward shift in the threshold of human hearing. Usually caused by being subjected to a loud sound. When the noise abates the hearing usually returns to normal. However continual exposure will cause the shift to be permanent.
See also • noise induced hearing loss
Time (t) one of the seven SI base quantities. The SI unit is the second, symbol s
A time domain graph shows how a signal changes over time, whereas a frequency domain graph shows how much of the signal lies within each given frequency band over a range of frequencies.
Time Domain Averaging is very useful in reducing the random noise components in a spectrum, or in reducing the effect of other interfering signals such as components from a nearby machine.
See also • other types of averaging
Time Frequency Analysis when analysing non-stationary signals, time frequency analysis gives optimum resolution in both the time and frequency domains. Data is presented in a map with time shown on the x-axis, frequency on the y-axis and the amplitude indicated by various colours or grey-scales in the contour map.
Time Integral an integral of a variable or function with respect to time
Time Series a sequence of measurements where a single measurement is not considered appropriate to establish the mean, maximum and/or other statistical information. In this case mean is used to differentiate the results from the wide range of averaging methods widely used in acoustical measurements.
Time Weighted Average (TWA) is the workplace noise exposure measured over an 8 hour working day, using a 3 dB exchange rate in Europe.
Time Weighting the time-averaging characteristic used to measure oscillatory or fluctuating quantities. Common time weightings are rectangular (perfect integration with no memory) and exponential. Exponential weighting provides a running average in which recent values are more heavily weighted than those occurring earlier.
Time Window Fourier analysis tells us that time and frequency are simply two alternative ways of observing a signal. By changing the nature of a signal in the time domain, we implicitly change the nature of the spectrum in the frequency domain. This is exactly what we do when we apply a weighting function or time window to a specified period of time record. Examples are rectangular, hanning, etc.
See also • windowing
Tinnitus ringing in the ear or noise sensed in the head. Onset may be due to an acoustic trauma and persist in the absence of acoustical stimulation (in which case it may indicate a lesion of the auditory system). Not directly due to external acoustic stimulation. It can be associated with exposure to high levels of noise.
Tone sound or noise recognisable by it's regularity. A simple or pure tone has one frequency. Complex tones have two or more simple tones, the lowest tone frequency is called the fundamental, the others are overtones.
Tone Assessment sound containing discrete frequencies or 'tones' has for many years (BS 4142, BS 7445 and ISO 1996) attracted a 5 dB penalty when assessing industrial and environmental noise.
BS 7445 suggests that if the level in a 1/3-octave band is 5 dB or more higher then the adjacent two frequency bands then it's likely to constitute a nuisance and should be rated accordingly.
Tone Assessment Measurements : some meters include software to make measurements directly.Parameters associated with Tone Assessment include
Kt : the value added to the LAeq to give the tone-corrected rating level
Lta : the audibility of all tones found in the same critical band as the selected tone
Lpn : the total level of the masking noise in the band containing the selected tone
Lpti : the level of the selected tone
Lpt : the total level of all tones in the critical band containing the prominent tone
See also • perceived noise level
Torque also called the moment of force is the tendency of a force to rotate an object about some axis. It is the product of the force and the length (radius) to the point where the force is applied.
The unit is the newton metre, N·m = kg m2 s-2
TNI = 4 (LA10 - LA90) + (LA90 - 30) dB
See also • maximum transient vibration value
See also • Sound Insulation Definition
Type 1 precision grade sound level meters for laboratory and field use - renamed Class 1
Type 2 general grade sound level meters for field use - renamed Class 2