Understanding notes

What is a note?

Let's see 2 notes:

These are 2 notes, what characterize them one from the other?
The fundamental frequency!

This means that we have an infinite amount of notes!

Now try these

They should sound right together.
Why? Because:

• 440 is the concert A or LA note. A frequency that was set arbitrarily so all musician can play the same notes. So you should be familiar with it.
• These frequency are all multiplied by 2
• I just told you so.
• You may have grown in a culture where these notes just sound good.

Not all instruments sound the same

But all instruments are tuned to the same notes, or the same fundamental frequencies.

All instruments have what we call "Timbre".
In reality instruments do not play pure fundamental frequencies. They play a multitude of frequencies at the same time, but all share the same fundamental frequencies and that's what they are tuned to.

Here are different sample of instruments played at the same fundamental frequency, 220Hz: