Definitions, Terms, Units and Parameters
OTo find specific terms on a page use CTRL+F
Octave: a range of frequencies whose upper frequency limit is twice that of its lower frequency limit. For example, the 1000 Hertz octave band contains noise energy at all frequencies from 707 to 1414 Hertz. In acoustical measurements, sound pressure level is often measured in octave bands, and the centre frequencies of these bands are defined by ISO - 31.5 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, 16 kHz to divide the audio spectrum into 10 equal parts. The sound pressure level of sound that has been passed through an octave band pass filter is termed the octave band sound pressure level.
Similarly, for one-third octave bands, there being three such bands in each octave band.
1/1, 1/3, 1/6, 1/12, and 1/24 octaves are used in acoustics.
Octave Band analyser: an instrument that measures sound levels in octave bands.
Octave Filter: a filter whose upper-to-lower passband limits bear a ratio of 2. Is preferably centred at one of the preferred frequencies given in ISO R266 and should meet the attenuation characteristic of IEC R255. Octave filters are used to make a real-time frequency analysis. These filters are called constant percentage bandwidth (CPB) filters. Octave filters can be divided into 1/3-octave filters, 1/12- or 1/24-octave filters, depending on the required analysis resolution.
Omni-directional Microphone: measures sound energy arriving from all directions equally. In order to comply with the standard requirements measurement microphones are omnidirectional unless otherwise stated. To achieve an omnidirectional response at all frequencies requires a special and therefore expensive microphone. See also our measurement microphones basics
Omni-directional Source: a source that emits equal amounts of energy in all directions and generates spherical waves.
Order Analysis: the analysis of harmonics related to rotational speed. The application of harmonic analysis to rotating machinery.
Order Tracking: order tracking is a special case of FFT analysis applied to variable-speed rotating machines where the sampling frequency of the analyser is varied to be an exact multiple of the running speed of the machine while a series of spectra are recorded. The spectra are usually shown on top of one another on the page, and this is sometimes called a waterfall plot.
OSHA: Occupational Safety and Health Administration : USA.
Overload: the input to the Sound Level Meter is too high for the current measurement range. Change the range.
Overload %: percentage of time an overload occurred.
Over-range: the input to the Sound Level Meter is too high for the current measurement range. Change the range.
Over-range %: percentage of time an over range occurred.
Overtones: are the harmonics or partials of a discrete frequency component. The first overtone corresponds to the second harmonic in a harmonic series.
Page Up l Glossary Search l Certified Instrumentation
This site is maintained by
Gracey & Associates 01234 708835
The Sound and Vibration Instrument Hire and Calibration Specialists
Instrument Hire | Calibration | Standards | Link to Us or E-mail US