4/7/2024 0 Comments Logarithmic decibel scaleUnfortunately, when specifying a decibel value, we often have no indication of what it refers to. A decibel value is always relative to something. Now things will get a bit abstract: There is no absolute sound pressure level that is referred to as a decibel. The logarithmic decibel scale is convenient when adding signal values like sound power, pressure and others from two or more sources. The filter output is simply accessed across the resistor instead of the capacitor. Dependance sound levels change factor perceived loudness decibel scale log compare intensities calculate power level formula noise volume doubling loudness. The decibel scale expresses a logarithmic ratio. Note that because the same resistor and capacitor were used, the cutoff frequency has not changed. Below is a Bode plot of the high-pass RC filter frequency response a few sections back.It makes things easier if a logarithmic scale is used this is what the decibel scale is. The ratio of intensities between silence and ‘ow that hurts my ears’ is about 1:100 million million. The cutoff frequency, which is 1592 Hz for this particular circuit, corresponds to a 3 dB attenuation, and can be used as a figure-of-merit for the response of the filter. The human ear is capable of hearing very quiet (low intensity) sounds and extremely loud (high intensity) sounds. This is the cutoff frequency, f 0, of the RC filter, which is expressed by the following relationship: f 0 = 1/(2πRC) The intersection point of these two lines coincides with the rounded section of the plot. Every Bode plot has two straight lines: the relatively flat response where little attenuation occurs and a linear response of -20 dB/decade at higher frequencies.Notice that low frequencies are unattenuated, but attenuation increases with higher frequencies. Below is a Bode plot of the low-pass RC filter frequency response shown a few sections back. The decibel scale is logarithmic because thats essentially how our ears respond.
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