Beats: play two sounds whose frequencies are Δf apart

f1 = 400;
s1[t_] = Sin[2π f1 t];
s2[t_,Δf_] = Sin[2 π (f1 + Δf) t];
Manipulate[Sound[{Play[s1[t]+s2[t,Δf],{t,0,10}]}], {Δf,1, 10, 1}]

Doppler effect: (Subscript[f, 1]) = ((Subscript[f, 0])/(1 - ((Subscript[v, source])/(Subscript[v, sound]))))

vsound = 360;
vsource[t_, v0_]= Piecewise[{{v0,t ≤5}, {-v0, t >5}}];
f[t_,v0_] = ((400 )/(1 - ((vsource[t, v0])/vsound)));
Manipulate[Sound[{Play[Sin[2π f[t,v0]t],{t,4.5, 5.5}]}], {v0,10,110,20}]