My name is Andrey I live in Prague, Czech Republicand today I want to explore something with you! click here Got it. Let’s go!
Before we start I need you to have an audio outputAre your speakers or headphones connected? click Yes!
Great!By playing sound I force the membrane ofyour audio output to move again? click! membrane I heard something!
You heard something? That means, that the membrane in your earcalled the eardrum is moving too eardrum That’s everyday stuff, but makes you wonder… Why is this happening?
The energy from the speaker is travelling as a wave, trough a medium, which is air, until it hits your eardrum we call that PropagationThere are air molecules right next to the membrane of the speaker.When the membrane moves, they ride it like a cowboy. air molecules Yeehaw!
As the air is getting more dense and less dense, *compressed * rarefied membrane air molecules the energy passes to adjacent molecules. *Notice, that molecules are moving back and for th, never actually moving too far away from their place!We call this type of wave LONGITUDINAL *it stretches forward, tries to become LONGER Got it
*which is approximately 1 foot per millisecond 1 kilometer in 3 seconds 1 mile in 5 seconds 340 meters per second Is the speed at which air propagates the energyThe speed varies with the density, temperature or even a humidity of air Ok.
The sound propagates not only towards you but in every direction! reflections sound source youAfter reflecting off walls and other objects the sound eventually reaches your ear.And your brain analyzes those reflections to create a sense and idea of space! Sweet!
Here is another wave type It moves perpendicular to the direction of the wave Like a whip or a stringWe call this type of waveTRANSVERSE but air molecules can’t do that! That’s simple stuff. Next!
Okay, so the membrane of the speaker moves, energy passes trough air molecules as longitudinal waves until it bumps into your eardrum, but..! what’s the difference between waves that sound like this or like that? click to play Tell me!
It’s all about the shape that waves form, or the waveformIf it consists of repetitive patters then it’s a tone If it’s made of chaotic patterns then it’s a noise What about different pitches?
The rate of repetition of a waveform pattern is called The lower the frequency, the lower the pitch. The higher the frequency, the higher the pitch. slower vibrations faster vibrations Got it
Frequency is measured in hertz Hz = number of repetitions per second Human hearing range is approximately from 20 Hz to 20 000 Hz Ok. What about load and quiet?
Very simple!If the membrane of a speaker moves more - expands further, it creates more significant changes in the air pressure We call that property of a wave AMPLITUDE and perceive it as LOUDNESS low amplitude, less pressure high amplitude, more pressure Ok.
Amplitude is measured in decibels dB and it’s a relative measureThat means, that it gets used differently in a varietyof contexts. Explain me that
Sure!In air we use dB Sound Pressure Level where 0 dB SPL is the threshold of hearing and 120 dB SPL is the threshold of pain In digital domain we use dB Full Scale where 0 dB FS is the loudest digital information and anything quieter goes into negative numbers That’s quite simple
Now let’s summarize! As the sound source emits energy waves, they travel trough a medium 340 m/s as transverse or longitudinal waves This is called Propagation Sure!
The rate at which sound vibrates is called FrequencyIt is measured in Hz and perceived as pitch. Next!
The amount of pressure, the power of a wave is called Amplitude Measured in dB and perceived as loudness. we use dB SPL in the air and dB FS in digital world That’s all?
Just remember one thing: Propagation, Frequency and Amplitude are completely independent on each other. Yes! If you want to find out more about sound, go to Coursera.org and look up course called Introduction to Music ProductionIt has been a great journey, thank you for your time and have a great day! Andrey click Bye!