![negative decibel scale negative decibel scale](https://cdn.shopify.com/s/files/1/0661/6399/8943/files/decibel-scale_480x480.jpg)
Why is it 20 log(x) and 10 log(x)? Essentially, because there’s an “x²” some of the physical properties which is getting log-ged out of the rest of the formula and put in front instead, with 10 log(x²)= 2*10 log(x) = 20 log(x). If the ratio is Y for powers, the dB expression is 10 log (Y). If the ratio is X for voltages, currents or pressures, the dB expression is 20 log (X). This basic unit is mainly used for losses, gains, return losses, etc., i.e., as a logarithmic ratio between two values which can be voltages, currents, powers, acoustic pressures, etc. From the same rec G.100.1 which specifies dBov: Slight aside: dB itself is ambiguous anyway. I suppose it technically is true, but it isn’t massively helpful because it’s rarely used. Most phones of the same model will be “close” and maybe “close enough”, but different brands/models of phones will have different microphone sensitivity. For measuring you’ll need an SPL meter to calibrate your phone. “Detection” is different from “measuring”. I am a mobile application developer and I want to make an application that detects noises. Peaks don’t correlate well with loudness so for example, if you normalize (“maximize”) all of your music for 0dB peaks, some songs will sound louder than others. With digital we are usually concerned with peaks because of the 0dB maximum limit. There is an additional complication… SPL loudness is usually averaged, and frequency-weighted because our ears are more sensitive to mid-frequencies. But there are calibrated USB microphones and associated software. Since there is no standard calibration you can’t normally measure acoustic loudness with a microphone and Audacity. If you turn down the digital level by 3dB (3dB more negative) the acoustic loudness also drops by 3dB. Acoustic loudness depends on many things… Your volume control, the gain and power of your amplifier, the sensitivity of your speakers, how close you are to your speakers, etc. There is no standard calibration between digital and acoustic levels. 24-bit audio files have “bigger numbers” than 8-bit files, but when you play the file everything is automatically scaled to match your DAC so a 0dB 24-bit file isn’t louder than a 0dB 8-bit file. With integer formats, 0dB is the “highest you can count to” with a given number of bits. It’s approximately the quietest sound that can be heard and SPL levels are usually positive.ĠdBFS (zero decibels full scale) is the digital reference and it’s the “digital maximum” so digital dB levels are usually negative. There are different 0dB references for acoustic, digital, and electrical levels.ĠdB SPL is the acoustic reference.