# Finding Tbeat for 2 waves of periods T1 and T2 using oscilloscope

I think I can be more clear by using the image

http://en.wikipedia.org/wiki/File:Beating_Frequency.svg,

which should be similar to what you see on the scope when you sum channels 1 and 2.

There are two characteristic time periods in this image, the time between consecutive black peaks, and the time between consecutive orange peaks. Measure both these periods with the scope. Which is which?
you mean one is T_beat and one is T_bar?

George Jones
Staff Emeritus
Gold Member

you mean one is T_beat and one is T_bar?
Yes!

in that case the black one is T_beat and orange is T_bar, is this correct?

George Jones
Staff Emeritus
Gold Member

in that case the black one is T_beat and orange is T_bar, is this correct?
Oops.

I know you're not applying this to sound, but I want to use sound as example. Two musical instruments that are not quite in tune play the "same" note. What do you hear?

Pitch is determined by frequency, and you hear the average of the two frequencies, i.e., the black. But you hear the loudness of the tone vary with time - loud, soft, loud, soft, ... This is the phenomenon of beats.

Loudness is determined determined by the orange "envelope", so this gives the period of the beats.

oh I see, so I got it reversed then.. orange is T_beat and the black one is the T_average... thank you so much for explaining this, I appreciate it