Good morning.
I'm Bo, this is my presentation on beat frequency for...
♪flipping physics♪
It's probably best to start by hearing what beat frequency is, so let's start with just a 440 Hz tone...
And then a 441 Hz tone...
And then let's play those two frequencies together.
What you hear is called the beat frequency.
The equation for the beat frequency is the absolute value of the differences - the difference
between the two frequencies which is why this beat frequency is 1 Hz or 1 cycle every second
and this is - this beat frequency is 2 Hz or 2 cycles every second.
And then 3 Hz and so on.
Now that you know what beat frequencies sound like, let's make sure you know why beat frequencies happen.
When two sinusoidal frequencies are close to one another in frequency, their two wave
patterns look like this...
Actually, let's overlap the two waves to better understand how the wave interference works.
Hopefully you can see that the two waves alternate between being in-phase and therefore constructively
interfering with one another to create a larger amplitude, and then being out-of-phase and
therefore destructively interfering with one another to create a smaller amplitude.
When this happens, the amplitude of the two combined waves increases and decreases at
the beat frequency and that is why you hear beats.
We can go back to the original example I had you listen to and show you the waveform for one beat.
You can see the waveform for one beat has the same shape as the black wave which is
the superposition of the two waves close to one another in frequency.
Again, because both waveforms show beat frequency.
The top wave is the audio recording of beats and the bottom wave is an ideal representation.
A practical application of this is that beats are a useful way to tune some musical instruments.
For example, on a guitar, the fourth harmonic of the low E string, is at the same frequency
as the third harmonic of the A string.
So, this is the E string and this is the first harmonic on the E string.
This is the second harmonic on the low E string.
And just so you know, I am holding my finger gently on the string and not pushing down
to create a node at this point and to force a harmonica at this point.
So this is the second harmonic, the third harmonic and the fourth harmonic on the low E string.
And this is the A string, so this is the first on the A string, this is the second harmonic
on the A string and the third harmonic on the A string.
Therefore, when you play the fourth harmonic on the low E string and the third harmonic
on the A string, you should not hear any beats because the two are in tune with one another.
However, if one of the strings is slightly out of tune, then what you hear... is beats.
And what you can do is you can then adjust the frequency so you no longer hear beats
and the two are in tune with one another.
One more time...
So, again, if one of the strings is slightly out of tune to the other one...
You can hear beats and what you can do is adjust the frequency so you no longer hear
beats and the two are in tune with one another.
A practical application of beat frequency...
Thanks for learning with me, it was fun... Yeah.