Test your lower and upper limit with this video:
A simple tone, or pure tone, has a sinusoidal waveform. A complex tone is any musical tone that is not sinusoidal, but is periodic, such that it can be described as a sum of simple tones with harmonically related frequencies.
A musical tone is characterized by its duration, pitch, intensity (or loudness), and timbre(or quality). The notes used in music can be more complex than musical tones, as they may include aperiodic aspects, such as attack transients, vibrato, andenvelope modulation.
Do, Re, Mi, Fa, Sol, La, Si
C, D, E, F, G, A, B
At the picture of the piano further down we start with the C2, and we also have C3, C4 and C5. Note that the A4 or A440 is termed "pitch standard" and serves as a general tuning standard for musical pitch. This is also the default for the tone generator online tool that will be mentioned further down.
Note the sine wave with a frequency of 65.41Hz corresponding to the marked key (Dp or C).
Someone says 'this music has a fast beat" meaning that one beat follows quickly after another. We refer to "beat" as the action of beating for instance a drum in a repetitive way. It is actually an alternation of loud and soft.
Also, in some cases a police car siren does not make a continuous sound, it makes a beat, a sound that goes from loud to less loud.
The definition of a beat is :"a rhythmic interference of close frequencies". We basically sum up the two waveforms and this results in parts where they reinforce each other so that we hear a loud sound and parts where they cancel each other out and we hear a weak sound. The alternation of loud and weak (or sound and no sound) gives us the impression of "beat".
Generate a beat from two tones using the http://onlinetonegenerator.com/ as mentioned in the following video https://youtu.be/i886Lbjbl9k (duration: 2min12s). Generate a tone of 440Hz (pitch standard for musical instruments) and at another browser window a tone of 441Hz. You will hear the beat and you can explore this further with the video mentioned further down.
Wave Interference & Beats: Generate a 440Hz & a 441Hz tone and listen to their beat that repeats itself every 1sec http://goo.gl/aA1MvO
Consider an electromagnetic wave of a frequency of 10533 MHz and another with a frequency of 10532 MHz. What will be the result of the interference of these? A wave with a frequency of 1MHz.
The two waves will beat against each other and they will produce a beat of 1MHz.
Watch the measurements at this 1:50min video https://www.youtube.com/watch?v=u_nmvA5KOkQ
Figure: One horn produces 10533 MHz waves and the other produces 10532 MHz waves. The researcher covers each of the two with his hand and verifies their emission using instrumentation.
Figure: The oscilloscope demonstrates the detected waveform. Upon interference (beats) a wave of 1096 Hz (1MHz) is measured.
The same phenomenon can be observed at this MIT video: