function?[SMR?min_threshold_subband?frame_psd_dBSPL?...
????masking_threshold]?=?MPEG1_psycho_acoustic_model1（frame）

%?function?[SMR?min_threshold_subband?frame_psd_SPL?...
%????masking_threshold]?=?MPEG1_psycho_acoustic_model1（frame）
%?Computes?the?masking?threshold?（in?dB）?corresponding?to?psycho-acoustic
%?model?#1?used?in?MPEG-1?Audio?（cf??ISO/CEI??norm?11172-3:1993?（F）?pp.
%?122-128）.?
%?Input?|frame|?length?should?be?512?samples?in?the?[-1+1]?range.?
%?|SMR|?returns?27?signal-to-mask?ratios?（in?dB）.
%?|min_threshold_subband|?returns?the?minimun?of?|masking?threshold|?in?each
%?of?the?32?sub-bands.?
%?|frame_psd_SPL|?returns?the?estimated?PSD?of?the?input?frame?in?dB?SPL
%?assuming?the?level?of?full?scale?signals?is?set?to?96?dB?SPL.
%
%?Copyright?N.?Moreau?ENST?Paris?19/03/02
%?Modified?by?Thierry?Dutoit?FPMs?Mons?03/05/07

global?LTq_i?LTq_k?Table_z?Frontieres_i?Frontieres_k?Larg_f

if?size（LTq_i）==[00]
???MPEG1_psycho_acoustic_model1_init;
end;

N?=?length（frame）;
if?N?~=?512
????disp（‘frame?length?must?be?set?to?512‘）
????return
end

%?FFT
%?***

hann?=?sqrt（8/3）/2*[ones（N?1）?-?cos（2*pi*（0:N-1）‘/N）];
if?sum（abs（frame））?>?0
????X1?=?fft（frame.*hann）;
????X1?=?（abs（X1（1:N/2+1））.^2）/N;
????perio_xn_db?=?10*log10（X1）;
else
????perio_xn_db?=?zeros（N/2+11）;
end
%offset?=?max（perio_xn_db）?-?96;
%X?=?perio_xn_db?-?offset;

%?NB:?since?the?absolute?acoustic?level?set?by?the?listener?is?not?known?by
%?the?MPEG?psycho-acoustic?model?it?assumes?that?the?level?is?set?such
%?that??a?full-scale?signal?corresponds?to?96?dB?SPL.?Since?16?bits?signals
%?have?about?96?dB?of?dynamics?this?implies?that?the?LSB?is?close?to?
%?the?absolute?auditory?threshold.
%?Since?the?absolute?value?of?input?samples?is?assumed?to?be?<1?a
%?full-scale?signal?i.e.?ones（1:512）?will?produce?a?PSD?peak?at
%?10*log10（512）=27.09dB.?Hence?the?96-27.09?dB?offset.
offset=96-27.09;
X?=?perio_xn_db?+?offset;
frame_psd_dBSPL=X（1:256）;

%?Tonal?and?noise?masker?detection?
%?*************************

%?Local?maximum?search?

max_local?=?zeros（250?1）;
for?k?=?3:250
????if?X（k）?>?X（k-1）?&?X（k）?>=?X（k+1）
????????max_local（k）?=?1;
????end
end

tonal?=?zeros（250?1）;
for?k?=?3:62
????if?max_local（k）
????????tonal（k）?=?1;
????????for?j?=?[-2?2]
????????????if?X（k）?-?X（k+j）?????????????????tonal（k）?=?0;
????????????end
????????end
????end
end

for?k?=?63:126
????if?max_local（k）
????????tonal（k）?=?1;
????????for?j?=?[-3?-2?2?3]
????????????if?X（k）?-?X（k+j）?????????????????tonal（k）?=?0;
????????????end
????????end
????end
end

for?k?=?127:250
????if?max_local（k）
????????tonal（k）?=?1;
????????for?j?=?[-6:-2?2:6]
????????????if?X（k）?-?X（k+j）?????????????????tonal（k）?=?0;
????????????end
????????end
????end	
end

%?Tonal?masker?detection

X_tm?=?zeros（2501）;

for?k?=?1:250
????if?tonal（k）
????????temp?=?10^（X（k-1）/10）?+?10^（X（k）/10）?+?10^（X（k+1）/10）;
????