I'm taking a multimedia systems class in my MSc Computer Science, and I'm having some trouble understanding the formula for the alias frequency - this could stem from my misunderstanding of the alias signal.
My understanding of an alias signal is that if you undersample your input signal (i.e. sample at a rate which is less than twice the maximum frequency) then we can get aliasing because we're not sampling frequently enough to capture the high frequency details. The aliasing signal is the result of taking these sample values and joining them with a smooth curve.
Therefore, the resulting signal has a frequency of half the sampling frequency, since a pure sinusoid will need two samples per oscillation (1 for each turning point) - this would mean that the alias frequency should just be a function of the sampling frequency.
The formula for the alias frequency is the absolute difference of the signal frequency and the closest integer multiple of the sampling frequency - can someone explain this to me? Thanks in advance!