Difference equation implementation for audio echo

How would I go about implementing these difference equations if x is some audio I recorded, a is echo feedback, and D is delay.

Difference equation 1: y(n)=x(n)+ax(n-D) Is this a difference equation for a single echo? I'm computing it like this, correct?:

b = [1, zeros(1, D), - a];
y = filter(b, 1, x)

Difference equation 2: y(n)=x(n)+ay(n-D) Is this a difference equation for reverberation? Not sure how to go about this one...