This is more easily written as 2.2 pF (pico Farad). However, often the physical capacitors exhibit values that are a small fraction of the base unit for instance, 0.0000000000022 Farad. The unit for the capacitance of a capacitor is Farad. Here is a list of numeral prefixes as defined by the SI-system: Notated by prefix: “2k” as “k” indicates a factor of 1000. For instance, “2000” equals “2 times 10 to the power 3” or written as “2*10 3”. A numeral prefix is practical as it makes it easier to understand extremely small – or extremely large – numbers.Ī prefix replaces the power notation. The bandwidth is expressed either in absolute value or relative in octaves (often in 1/1 octave, 1/3 octave or fractions of an octave expressed by decimal numbers, for example, 0.1 octaves).Įxample: (1/1 octave ~ 70%, 1/3 octave ~ 22%).Ī filter’s Q factor is calculated like this:Ī prefix is an affix placed before a word or a number to modify its meaning. Here are the relations between the different terms:īandwidth is the frequency span between the -3 dB cutoff points on a response curve, i.e., f upper - f lower. On some devices though, you can switch between them. However, it depends on the filter brand, model and application which parameters that apply. Bandwidth, Q-factor, and percentage express the same thing. In filters defined for measurement techniques, also a percentage may apply to describe the bandwidth. The control parameters provided are frequency, level, and Q-factor or bandwidth. Parametric equalizers typically include bell-shaped filter responses, bandpass/stop filters. This absolute value applies, for instance, to the specification of microphones’ sensitivity. Describing the level of sound pressure, “dB re 20 μPa” also can be written as “dB SPL” (Sound Pressure Level).įor electrical measurements, another reference is 1 Volt, written as “0 dBV” or “0 dB re 1 Volt”. Now 0 dB means that sound pressure is present, and it is 20 μPa (approximately the threshold of hearing at mid-frequencies). You can make dB an absolute scale by applying a reference - for instance, the sound pressure level, the reference being 20 μPa. Any negative dB number indicates a negative change (the value is lower than before). Any positive dB number indicates a positive change (the value is higher than before). The most significant dB-number you will find in real life is <200 dB, meaning, if the dB number has three digits, the first always being “1”. By and large, each step on the scale is perceived as equal in size. 10 dB is subjectively perceived as a doubling or a halving. The advantage of this scale is that 1 dB is about the minor change of level you can hear. Thus, the scale is logarithmic, which provides the perception of equal-sized increment. The decibel scale is related to the way humans perceive level. Regarding frequency, we read the frequency response curve using a logarithmic scale. Humans perceive both level and frequency in a logarithmic manner. or ratio 2, the units are: 1-2-4-8-16, etc.) This logarithmic scaling applies to many electrical or acoustic measures, which specify microphones (i.e., Volt, Pascal, etc.). The logarithmic scale has a fixed ratio between each unit of the scale (e.g., ratio 10, the units are: 1-1, etc. There is a fixed interval between each unit of the linear scale (e.g., 1, 2, 3, 4, where the distance between each unit is 1). The table below shows filter order and the affiliated slopes (here attenuation) defined by dB/oct or dB/decade.Ĭonversion table: Filter slopes defined by filter order, dB/oct or dB/decade. Today these filters are typically only found in passive loudspeakers, whereas most filters are made digitally via DSP power. A second-order filter includes two of these components in combination with a resistor, like two capacitors or one coil and one capacitor: The slope obtained then is ☑2 dB per octave. The slope is ☖ dB per octave depending on the configuration of the two components. This component is usually a coil or a capacitor in connection with a resistor. A first-order filter, in principle, contains one electronic component which has a frequency-dependent resistance. The order of a filter defines the slope outside their passband. The frequency range of the human ear is approximately ten octaves or three decades from 20 Hz to 20000 Hz.įig 1 Number line marked with octave and decade intervals. A decade is defined ten times (or a tenth of) any quantity (or frequency range) this means the values are not fixed, but relative. However, in other fields within electronics, we describe the slope per decade, like 20 dB per decade.Īn octave is defined as a doubling or a halving of a value of frequency. When describing the attenuating, or gaining slope, of a filter in audio, it is common to define it by “dB per octave” like 6 dB per octave or, in short form, 6 dB/oct.
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