a signal x(n) then is this concept of shirting and folding correct?

Question

x(n) is given

need x(-n+3)

so to solve it:

• first advance the x(n) signal by 3 units(time)
• then fold it, or make a reflection of it

are the above steps correct or is the following correct

• first fold the x(n) signal
• then advance the signal by 3 units

?

Answer 1

Yes, this is a common source of confusion when learning about signals. Here's what I usually do.

Let y[n] = x[-n+3]. Because of -n, y[n] is obviously a time-reversed version of x[n]. But the question about the shift remains.

Notice that y[3] = x[0]. Therefore, y[n] is achieved by first reflecting x[n] about n=0 and then delaying the reflected signal by 3.

For example, let x[n] be the unit step function u[n]. Draw x[n], then draw y[n].