Audio Basics

Humans can hear sounds from approximately 20Hz to 20kHz (20,000).

Or

The sounds that a human can listen to are within approximately 20Hz to 20kHz.

The word "approximately" is used because some people can hear lower than 20Hz, while some others may be able to hear over 20kHz.

The "range" varies between gender and age. Village women can hear over 20kHz very well, while little infant can hear both below and above very well. That is why they cry easily.

A good friend, (you know how you are :)) has asked, where did I "guess" infants can hear below 20Hz? and he is right to say I guessed. 

I guess - based on humans hearing in the brain is from electrical pulses generated by vibrations, therefore infants with an extremely sensitive new body external and internal will be susceptible to any and all forms of vibration. Even the slightest ones. Therefore picking up signals as sounds in the brain. Now it is your call to believe what I say, of figure out the answer for yourself :) [I'll get his permission before putting his name up for credits]

Each sound or (frequency more technically) can be loud or soft. The level at which they are made is scaled as dB. Humans generally speaks around the levels of 70 to 75 dB SPL.

dB = deci-Bel by Alexander Grahembell. deci = 1/10, Bel is his surname.

SPL = Sound Pressure Level.

With these information, sound may be represented on a graph consisting of level in dB SPL versus frequency. If all sounds have the same level then it would appear as flat frequency response, which looks like: -

It is to be stressed that sound, is a in-depth complicated subject and must be understood with all principles of acoustics, audio technology, human psychology and much more.

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