function output = adpcm_f(a1) % % adpcm_f(a1) % returns 4a1 if |a1|<=2^-1 % returns 2*adpcm(a1) if |a1|> 2^-1 % if abs(a1) <= .5 output = 4*a1; else output = 2*adpcm_sgn(a1); end