Why RG 89.0 dB when it doesn't clip?
Reply #29 – 2008-06-04 04:58:13

Note that, in his great explanation, Dynamic has snook (is that the past tense of sneak?) in yet another scale - something related to (but not exactly) dB / Hz - loudness per frequency bin. Oh yes. The unit of dB / Hz is commonly used in engineering but it comes with danger for misunderstanding or unclear thinking, for you don't divide the number of decibels by the bandwidth as the units alone would tend to suggest, but must convert out of the logarithmic domain into linear power units or linear power ratio, which is why my explanation had to subtract 10 * log (512) in the decibel domain to divide the white noise power equally among 512 bins in the power spectrum. I hope this small digression is acceptable in the Scientific/R&D sub-forum. As David has pointed out the while dB based units can be really handy you need to be careful to think about the fact it's just a power ratio expressed in logarithmic terms and that to do any other mathematics based on these figures, you should convert into the linear domain first. You must also bear in mind the reference level you are implicitly making the ratio relative to. Furthermore, bear in mind that to Joe Public, there's little understanding of dB's peculiarities (rather like other logarithmic scales, such as the Richter scale for earthquake power, or like non-absolute linear scales like temperatures in °C or °F). A 4.0 earthquake is 1000 time less powerful than a 7.0 earthquake, I believe. It's not "twice as hot" in Madrid as in Oslo when it's 32°C and 16°C respectively (90°F and 61°F respectively, or in absolute temperature, 305 Kelvin and 289 Kelvin respectively).