| ▲ | rocqua 2 days ago |
| Decibels in gain, those are fine. Though they use a silly base. dBm makes a decent amount of sense, given the RF background.
The fact that decibels work differently for voltage and power is very weird, but understandable in isolation. But audio decibels are horribly underspecified. And any other use of a decibel as a dimensionful unit is horrible.
I think the RF people know, and that's why they use dBm. Any system that uses decibels as dimensional units needs to make their baseline clear. I recently saw a fan advertising a low decibel noise "at 3 meters". And it's nice that they advertise (part of) the baseline, but it sweeps a ~10db difference in pressure under the rug, comparee to the standard 1m reference. |
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| ▲ | mikewarot 2 days ago | parent [-] |
| Decibels aren't units... they are ratios. The ratio could be gain, or loss, or compared to the noise floor, or the signal of interest, or a standard unit, such as Watts, milliWatts, or microVolts into 50 ohms. >The fact that decibels work differently for voltage and power is very weird, but understandable in isolation. If you have a given load, increasing the voltage by a ratio of 10:1 (20 dB) is exactly the same as increasing the power by a ratio of 100:1 (20 dB) (because increasing the voltage ALSO increases the current, and the power is the product of the two) |
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| ▲ | margalabargala 2 days ago | parent | next [-] | | > If you have a given load, increasing the voltage by a ratio of 10:1 (20 dB) is exactly the same as increasing the power by a ratio of 100:1 (20 dB) (because increasing the voltage ALSO increases the current, and the power is the product of the two) It's not that we don't understand this. We do understand this, and simply think it's ludicrous that the same nominal "unit" is used to refer to both, rather than calling the voltage one, say, "hemidecibels". Because we're not talking about power always, we're talking about, as you say, ratios. | |
| ▲ | IsTom 2 days ago | parent | prev | next [-] | | > Decibels aren't units... they are ratios. Until they are a ratio to a specific arcane reference level as mentioned in the article. | | |
| ▲ | grues-dinner 2 days ago | parent [-] | | It's not that arcane, it's referenced to a sound pressure level of 1 pascal. Which, yes, is still arbitrary in that it all ends up back at the arbitrary values of things like metres, seconds, kilograms, etc. Volts per pascal might make sense in some contexts (like your input buffer power supply), but log volts per pascal makes sense in others, particularly for audio applications where you stack gains and attenuations onto an already-logarithmic domain. | | |
| ▲ | wl 2 days ago | parent [-] | | dB SPL is referenced to 20 µPa, not 1 Pa. You might be confused by the fact that the 94 dB SPL (1 Pa) is the default for microphone calibrators and specifying microphone sensitivity. | | |
| ▲ | grues-dinner 2 days ago | parent [-] | | I was referring to the latter, which is why volts are involved at all. But I suppose if they'd chosen to follow the SPL zero point for the voltage-pressure scale as well as the absolute pressure scale that's would be equally arbitrary in its own way, even if more consistent in another. |
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| ▲ | ajuc 2 days ago | parent | prev [-] | | Would you defend using pound for force and mass because "it's often the same"? |
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