- [Narrator] When we speak of sound coming from a speaker,
we're really talking about those waves
of high and low air pressure
traveling through the air
that makes our eardrums vibrate in sympathy.
The speed of the vibration is perceived
as a particular tone.
Hertz is the name given to anything
that happens multiple times per second.
So something that's 50 Hertz happens 50 times a second.
The surface of a speaker has a resting position
that we'll call zero.
It moves out from zero
to increase the air pressure
and moves back through zero
into the body of the speaker cabinet,
to create low air pressure.
Finally, it returns to its zero-point again.
That's one full cycle.
And because the movement is cyclic,
it can be measured in degrees.
Like a circular motion.
Our ears can hear something like 20 Hertz to 20,000 Hertz
though, as we age, the highest frequency we can hear
goes down.
For what it's worth,
most of the energy in speech is around 300 to 500 Hertz.
And most of the detail is around one kilohertz range.
That's one thousand Hertz.
That's why telephones place most emphasis
at around about the one kilohertz territory.
Let's look at some sounds with a tone generator.
Here's 100 Hertz. 50 Hertz. 1 kilohertz.
There are a few useful ways of turning frequency
into visuals.
This frequency analysis panel shows amplitude
on the vertical access,
and frequency on the horizontal access.
Here's a little bassline.
(low rumbling)
And you can easily see the frequencies it covers.
The spectral frequency display is a little like
a regular waveform,
in that it shows you the amplitude over time
But now, instead of the vertical access showing
how loud the audio is,
it's a measure of the frequency.
The brightness of the dots indicates amplitude
at those frequencies.
(low rumbling)
Here's that bassline again.
It's pretty loud,
but only at lower frequencies.
I think the word frequency makes audio seem complex,
for me, it comes across as technical, scientific language.
And as the great scientist Tesla said,
"If you want to find the secrets of the universe,
think in terms of energy, frequency, and vibration."
But actually,
the basic concept is very simple.
Bigger numbers means more cycles per second,
which we perceive as a higher tone.