![]() That 0.5 is a scalar value in amplitude space. ![]() So, there’s our answer… the maximum output level of this particular FAB Module setup (using a +/-15VDC power supply) is +21.313dBu.If you are a programmer, chances are that when you think of volume or volume adjustments of audio signals (or other streams of data), you are thinking in terms of amplitude.įor instance, to make an audio stream quieter, you are probably going to multiply all the samples by 0.5 to bring it down in volume. We’re not yet done… now, we need to compare this against our reference voltage which is 0.775Vrms (so we can get the dBu number). We need to convert this Peak-to-Peak voltage to RMS (Root Mean Square), or average. So the scope measures 25.5Volts Peak-to-Peak… meaning, from the highest point in the waveform, to the lowest point. So I adjusted the Gain Potentiometer so I can view the maximum sine wave signal on my scope, without any clipping. If our power supply voltage is higher, the maximum output level we’ll achieve will also be higher.) Here’s our setup: (Remember, we’re only working with a +/- 15VDC power supply. Remember, dBu is referenced against 0.775V rms, while dBm is referenced again 0.775V rms (loaded with 600-ohm). what is the maximum level it can output? For this purpose, dBu or dBm is typically used. Now, what if we want to measure the maximum voltage output capability of our FABModule. Because we’re just comparing 2 numbers against each other.įine. ![]() Note, we just use the plain dB symbol here (without any suffix). If Vin = 1Volt, and Vout = 2Volts, then Voltage Gain = 2. Gain (dB) = 20 * log (Vout/Vin) = 20 * log (Voltage Gain) To convert this to decibel, use the formula: how much bigger is the output signal compared against the input signal? So now, how can we measure the GAIN of our FAB Module? i.e. There are other “reference” numbers dB is used for, but for audio work, dBu and dBm (and plain old dB) are the most commonly used. Think of “dB u” as unloaded, and “dB m” as loaded with a 600-oh m resistor. Basically, we’re comparing against 0.775Vrms but LOADED with a 600-ohm load/resistor. the 1st number we’re comparing against.ĭBu = we’re comparing against 0.775Volts RMS as our 1st number.ĭBm = we’re comparing against 1 milliWatt of power. By adding a suffix to “dB”, we’re basically indicating to the reader the reference number/quantity, i.e. this is when we add a “suffix” to the plain old dB. Since plain old decibel (dB) is just a RATIO between (2) numbers, how can we communicate more clearly what kind of numbers are we comparing?Īhhh…. Taking it to the extreme, if our output signal is 1,000x larger than the input signal, that’s a 60dB difference (or gain). If the output signal is 10x the input signal, that’s a 20dB difference (or gain). A decibel allows us to compare 2 numbers logarithmically, comparing 2 numbers whose ratio are either very, very small or very, very large.įor example: If we’re talking about amplitude (basically, our waveform), if our output signal is 2x the input signal, that’s a 6dB difference (or gain). Example: Instead of saying the 2nd number is 2X the value of the 1st number, we say it’s 6dB larger, or 6dB more. Wikipedia says: The decibel ( dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level.īasically, it’s saying that decibel is nothing but a RATIO between 2 numbers. Okay, how do we find out what’s the maximum output capability of your FAB module system? To answer this question, we first need to segue and talk about decibels.
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