Sine wave interference - frequency analysis

[Dar_Bahatt]

I am trying to extract the low frequency
component of the sum of 2 sine waves.
For example - adding 40Hz and 50Hz
sine waves results in a 10Hz envelope.
I tried may frequency analysis VIs that
are part if Labview. All show the 40 and
50Hz components but not the 10Hz
component. Any idea why this happens?

[Norbert_B]

How comes that you think that there is a 10Hz component?

Why should the analysis function return a value which is not present?

EDIT: Just came up: I think you want to MULTIPLY the sine signals in time domain. This is a frequency modulation which will result in 10 and 90 Hz sine signals as result.

[johnsold]

Norbert is right. A linear operation like addition does not create any new frequency components not present in the original signals. Multiplication (including squaring) and other process like clipping will generate components at other frequencies often including the sum and difference frequencies.

Lynn