Guide to Understanding Decibels for Music Production | DAW (dB)

You would have come across this numerical unit on countless occasions in various articles in Loopazon. Probably a good percentage of readers would have guessed what it conveys as they have seen it before. But many of you would have not necessarily understood how it is calculated or expressed. This is quite natural and you need not really be an expert with equations and formulae in physics to be a music producer. However a basic understanding about the unit could benefit you on some occasions, especially if you are planning to upgrade your studio gear or contemplating making additions to it.

If you delve into the equations it may seem very complex. But to start with, you would have observed that these numerical values are often represented as decimal values. This is because, contrary to common misconception, the decibel (db) is not always about your volume levels or noise. It is a ratio. An arithmetic comparison of the power of a sound signal to a level represented on a logarithmic scale.

10log₁₀ (S₁/<emS₂) is how this ratio is arithme</spantically represented. S1 and S2 obviously are the intensity of two sound sources.

Decibel got its name from Alexander Graham Bell, the inventor of the telephone.

The original unit was Bel. This was used to calculate signal losses in early telephone lines. This was because soon after the invention of the telephone, it was discovered that different types of cables give different results. ‘Deci’ obviously implies that the decibel is 1/10th of a Bel, I.e, 6 dB is actually 60 Bels. However the Bel unit is rarely used. You would seldom find audio equipment manufacturers using the Bel as a numeric representation.

When discussing about condenser microphones, we did discuss about -10 dB, -20 dB pads or attenuator pads. It was mentioned that the attenuator pads are used to reduce distortion in loud sources.

Read: Guide to Condenser Microphones for Home Recording

Here you would have observed that these values do not have a suffix other than the dB. However often they are represented as dBV and dBM, in which the suffixes are absolute units of power, like Volt and Milliwatt.

Now, let us not complicate things here. What we aim with this short discussion is to have a basic understanding about decibels in music and audio production. The decibel is used in the audio equipment industry to represent the Sound Pressure Level (SPL), which is obviously the volume or loudness of a sound source. The ‘threshold of hearing’ is the minimum value that can be heard and perceived by the human ear.

And this is 20 micropascals approximately. The maximum value of sound that can be heard or perceived by humans is more than 60 million micropascals. This overwhelmingly wide dynamic range can be extremely difficult to be directly represented. Applying logarithmic functions gives more practically representable figures. The logarithmic equation you saw above might make more sense to you now. When a logarithmic function is applied, the sound pressure level is calculated as follows:

Sound Pressure Level = 20 log₂₀ (S_{1 (measured pressure)}/S_{2 (reference pressure)})

In the above equation, the numerator “measured presure” is the absolute sound pressure while the denominator “reference sound pressure” is the “threshold of human hearing” which we have discussed above (20 micropascals approximately). Now the result is a much more practically representable and discernible dynamic range value; 0 dB and 130 dB (instead of 20 micropascals and 60 million micropascals). This certainly makes sense to not just people working in the music and audio production industry, but also the layman who is window-shopping in electronics stores. Yet again, the dB is not an exact representation of loudness or volume because, it is not an absolute value. It is a value that you get after having performed the above logarithmic function. A 40 dB speaker you chance upon in an electronics store is not exactly twice as loud as the 20 dB speaker you find on the next rack.

When you multiply the threshold of human hearing (20 micropascals) into 10, your decibel value increases by 20 dB (from 0 dB to 20 dB). Now if the threshold of hearing is multiplied by 100 instead of 10, your decibel value increases to 40 dB. See the difference here, 20 micropascals multiplied by 10 is 200 micropascals with the decibel value being 20 dB. When the same threshold value 20 micropascals is multiplied by hundred, you get 2000 micropascals , with the decibel value being 40 dB. Previously, seeing 40 dB in a speaker might have given you the impression that is is twice as loud as your 20 dB speaker. But when calculated in micropascals, you clearly get to know that your 40 dB speaker is ten times louder than your 20 dB speaker. Similarly if you multiply the threshold by 1000, you get 20,000 micropascals with the decibel value being 60 dB. Thus contrary to your possible previous perception, a 60 dB speaker is not thrice, but a 100 times louder, than your 20 dB speakers. This is why we say that the dB is not an ‘absolute’ value. It is a representation rather than a real numeric unit. When you double your sound pressure, the sound pressure level (SPL) is increased by 6 dB. Let us see how this is represented in some of the things that we relate with:

Please note that these are all approximate values and we are using Pascal instead of the micropascal unit to make things easier. Before going further, please do keep in mind that, 1 pascal is a million micropascals. 

1. Your bedroom at midnight: 30dB (decibels) or 0.00063 Pa

2. Talking in normal volume from a 1 meter distance: 60 dB or 0.02 Pa 

3. Vacuum cleaner at a 1 meter distance: 70 dB or 0.063 Pa 

4. A moving car being heard from a 7 meter distance: 60 dB or 0.02 Pa

5. A library: 40 dB or 0.002 Pa 

6. A commercial truck in a highway: 100 dB or 2.0 Pa  

7. An electric drill: 100 dB or 2.0 Pa

8. A jet plane at 50 meter distance: 140 dB or 200 Pa 

9. A human whisper: 30 dB or 0.00063 Pa 

10. A motorbike on a highway: 90 dB or 0.63 Pa 

11. A train (diesel) from 30 meters: 80 dB or 0.2 Pa 

12. A Formula One racing car: 130 dB or 63.2 Pa

The threshold of ear pain for humans is, a loudness of anything between 110 dB and 140 dB. Anything above 150 dB is often considered life-threatening. Prolonged exposure to sounds above 80 dB could potentially lead to gradual hearing loss and anything above 100 dB is the threshold of intense discomfort.

This much information would suffice for a basic level of understanding about decibels unless you have a deep academic interest on the subject.

Also read: Beginner's Guide to Electric Guitars