If in Digital Sound Software there’s a meter from -60 to 0, what’s the best “range” (for the lack of knowledge) of sound someone can record at? Considering that people who will listen to that recording can adjust their speaker volumes up and down.
In: Engineering
0 is nominal sound. Thats the volume of the source, without any additional amplification or reduction. So you can add decibels or subtract them, which is why 0 is on the middle of a soundboard fader. Decibels also refer to general sound. You can’t really explain what it is without getting into sound pressure level and such. But its basically a measurement of “loudness.” A normal conversation between two people = 60db. A jet engine is about 140. Just know that while you record something, it has an inherent value in db. Then, when you put it through an audio system, if the system is set to 0, you’re going to hear it at the same volume that you recorded it in.
dB are a way of listing relative values that cover huge ranges
A sound at 60 dB_spl is 1000 times louder than the quietest sound you can detect. A jet engine at 140 dB_spl is 10,000,000 louder than the quietest sound you can hear. Negative dB levels are smaller than their reference level.
The trick is figuring out what the reference level is. For sound it’s the smallest pressure change you can hear so sounds you can hear are positive dB values while ultra quiet rooms have negative values. Amplifiers show their output relative to their maximum output so their numbers are usually negative
So why are dBs helpful? Because many of our senses also work on a logarithmic scale like dB. You perceive a sound to be twice as loud when it has increased by 10 dB. It’s easier to work with a calm room being 30 dB and a conversation being 60 dB than 632 uPa and 20 mPa
dB is a relative scale that scales up logarithmically. In sound equipment the reference pressure is often implied which is wrong as there are no standard. Most likely the dB on your equipment are dBa which are adjusted for human hearing. Because it is just a relative scale you can have negative values, it just means that relatively to the reference the sound you are producing has less pressure.
A dB is a deci-bel meaning 1/10 of one Bel. It refers to a certain standard of measuring pressure or power.
If your recording software has meters that show -60 to 0 dB, it shows how much headroom you have left or available before distortion occurs- record so that average levels are somewhere between -24 and -14dB without ever hitting 0dB. That dB is referred to as dB(FS) meaning “tenths of a bell below full scale” and an average of between -24 and -14 will correspond with 0dB on a VU (Volume Units) scale, the oldschool kind with a needle that moves.
First of all, what we perceive as sound are air vibrations, meaning diferences of air pressure reaching our eardrums and making moving it. Mark this!
dB is a relative logarithmic scale. Let’s go by parts! First it is a relative scale, meaning there is a reference sound used as the fractional base. Let’s say there is some reference sound with “power” (that will be defined afterwards) p0. We can measure all sounds as how much they are more powerful or less power full than p0 using fractions. For example, let’s say there is a sound 10 times as powerful as p0, we can say the power p of the sound is:
p= 10 x p0
Or:
p/p0 = 10
So, if we have a known reference sound, we can always explain how loud another sound is as a multiple of the referente sound. In this case the sound is 10 times the reference sound. This would be perfect if we where talking about linear things, but a lot of thing are not. When we talk about sounds in specific,the pressure difference in air is the most physically meaningful thing to talk about, but if we take a sound wave with the double of the air pressure difference it will not sound 2 times louder to us. Actually the loudness we fell in sound follows a logarithmic scale. Meaning, if we take a sound and make the difference of pressure 10 times greater, we will feel it as twice as loud. If we we take a sound with 100 times the difference in pressure, we will feel as trice as loud. There is a mathematical function that perfectly reproduces this. It’s the log function. The log function tells us what power we must use to the make a number reach it’s argument. For example:
log10(10) = 1, because 10^1 = 10
log10(100) = 2, because 10^2 = 100
We could use any base number, but the Bell scale usually uses the base 10. So, if we take a reference sound with pressure difference p0, and another sound with diference of pressure p, the power of the sound p in the Bell scale would be:
B = log10(p/p0)
But the Bell scale can be to large to be useful, so we divide the Bell scale by ten, building the deciBell scale (deci means a “tenth of”):
dB = log10(p/p0)/10
This is the meaning of the dB scale. Negative values means that the sound power you measured is lesser than the reference sound. For example, let’s say you measured a sound 10 times quieter than the reference sound (p = p0/10). The equation above would be:
dB = log10(p0/(10*p0)/10 = log10(1/10)/10 = -1/10 = -0.1
Notice that the dB scale is zero when the measured sound is as loud as the reference sound, positive when is louder and negative when is quieter.
Now, you may ask what is the reference sound for the dB scale. Well, it’s complicated and I think it is outside the scope of the question! But I’ll give a fast explanation. The Bell and the deciBells scales have their name because they created in the Bell Labs as a measure of signal power in telegraphs lines. As an electric signal is propagated through a wire, some of its power is lost due to electric resistance that converts part of the electric energy into heat. When telephones where invented, the dB was used as a measure of how much loudness reached a far telephone compared to the loudness of a person speaking. But loudness is related with sound wave’s energy and it depends on its frequency. So dB scale also depends on the sound frequencies!
Nowadays we consider that p0 is the power of a sound wave with 1 microPascal RMS of pressure diference in water, or 20 microPascal RMS of pressure diference in the air. RMS is another complication that is also out of scope, so I’ll omit unless you want a more in depth explanation!
But, in specific, sound recorder softwares, go from negative to zero, because it considers the maximum loudness it can capture as reference. Meaning, negative infinity is absolute silence and zero is the loudest sound it can capture. So, if you want a good range of quietness and loudness and/or no distortion, you should never reach zero in any sound frequency. If you do, the wave form will be “clipped”, so louder sounds will sound “square”, rough, distorted.
One good reference: [https://en.wikipedia.org/wiki/Decibel](https://en.wikipedia.org/wiki/Decibel)
dB are a relative scale, so you need to know what it’s relative to for it to make the most sense.
For digital audio the reference value is usually “full scale” or the maximum loudness of any single sample.
This could be denoted as dB FS.
So, 0 is the biggest value and all other values are lower, hence they are negative numbers.
Sound levels, as per your conversation example, are typically measured relative to 20 micro pascals, which is roughly, the quietest sound humans can hear.
Most sounds are louder than that, so we get mostly positive numbers.
With digital audio recording, it is crucial to not clip the signal. Clipping is when the sound tries to be louder than 0dB, so the wave form gets held back at 0dB. Graphically, a sine wave has the top and bottom of its curve clipped off, hence the name.
As long as it doesn’t clip, you can in theory go as close as you like to 0dB.
In practice, recording engineers will usually aim for around -18dB, so that any unexpectedly loud signal does not clip.
Bear in mind though, that the recordings are often then processed/mixed and the finished version will often have a peaks of -0.1dB or 0dB.
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