Video and radio do match impedance, so it matters what impedance you're using, and that it be matched correctly as well.) BTW, for the acoustic analogy of impedance, consider the product and ratio of velocity and pressure (the electrical analogs of current and voltage). dB volts would make more sense in such a case. ![]() (Audio systems typically do not match impedances, using a low source impedance, and a >= 10kohm load impedance. Typical system impedances are 600 ohms (telco, audio), 75 ohms (video, CATV.) and 50 ohms (radio, test equipment, general?), but others might be snuck in: be careful and inspect what the aim of the circuit/system is. dB with electrical references are common: dBm (1mW at whatever the system impedance is - if you're measuring voltage or current instead, the impedance matters!), dBuV (0 dBuV = 1 microvolt, note this does not include system impedance so is not also a measure of power), and so on. If you've been using acoustic dB, that's probably referenced to 0dB = threshold of hearing, give or take (which is some convenient acoustic pressure or power level I forget). Usually, the sensitivity factor is measured at 1kHz.) ĭBs are used exactly as you have been using them: a logarithmic measure of intensity. (It's a little more complex than that since the "A" is not a constant but rather a curve that tries to approximate the frequency response of the human ear. Or you can put in -98dBm (that's a *tiny* signal!) and get 0dBA or a sound that theoretically can just be heard. They have a sensitivity factor of 98dB, meaning that you'll get a very loud 98dB sound if you put in 0dBm or 1mW. As for an example where dBA and dBm meet, let's take a look at some Xiaomi Piston 3 headphones. For example, if you put a 10dBm signal into an amplifier with a 10dB gain, you get a 20dBm signal out. That's handy when it comes to calculating levels as it lets you use simple addition rater than multiplication. Also very common is dB used to express gain or attenuation. In electronics, dBm is a very common unit and that refers to dB referenced to a milliwatt. The "dB" that refers to sound volume is actually dBA, referenced to the accepted "noise floor" of the human ear. DB is nothing more than a concise way to express a wide range of ratios.
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