%(MM1803.m plot)
Hz=[20:10:100 200:100:1000 1500 2000:1000:10000]; % frequencies in Hertz
spl=[76 66 59 54 49 46 43 40 38 22 ... % sound pressure level in dB
 14 9 6 3.5 2.5 1.4 0.7 0 -1 -3 ...
 -8 -7 -2 2 7 9 11 12];

Hzi = linspace(2e3,5e3); % look closely near minimum
spli = interp1(Hz,spl,Hzi,'spline'); % interpolate near minimum
i = find(Hz>=2e3 & Hz<=5e3); % find original data indices near minimum

semilogx(Hz(i),spl(i),'--o',Hzi,spli) % plot old and new data

xlabel('Frequency, Hz')
ylabel('Relative Sound Pressure Level, dB')
title('Figure 18.3: Threshold of Human Hearing')
grid on
