calculating snr in delsig toolbox

[sona_]

hello
i was simulating of a first order adc using code given in book of richard scherier. for calculating SNR he uses (page 265)
snr = calculateSNR(spec(1:ceil(Nfft/(2*OSR))+1), tone_bin)...
where spec is spec = fft(v.*ds_hann(Nfft))/(Nfft*(nLev-1)/4);
well i don't understand this.if i calculate my SNR using the standard formulae of
(3.3L+1.6)log(OSR)+quantizer bits+1.6log(2L+1)-1.6L where L is the order i get completely different results.
thanx i

 

[sona_]

also as i calculate snr from the above code ideally the complete range of snr for different OSR of the second order sigma delta modulator should be high as compare to the ist order sigma delta modulator.but m getting lesser SNRs for 2nd order than ist orders