Mel filter bands found by psychological and instrumentation experiments) Freg lower than 1 KHz Filter has narrower bands and output Mel filters in linear scale Higher frequencies have larger bands and in log scale) · More filter below1KHZ 05 Less filters above 1Khz 03 1000010002000300040005000600700a900 Frequency(Hz) Feature extraction v 9a http://instructl.cit.cornelledu/courses/ece576/finalprojects/f2008/pae26_jsc59/pae26jsC59/images/mElfilt.png
Mel filter bands (found by psychological and instrumentation experiments) • Freq. lower than 1 KHz has narrower bands (and in linear scale) • Higher frequencies have larger bands (and in log scale) • More filter below 1KHz • Less filters above 1KHz Feature extraction, v.9a 11 http://instruct1.cit.cornell.edu/courses/ece576/FinalProjects/f2008/pae26_jsc59/pae26_jsc59/images/melfilt.png Filter output
Mel scale melody scale Fromhttpsen.wikipedia.org/wiki/melscale Measure relative strength in perception of different frequencies The mel scale, named by stevens, Volkmann, and Newman in 1937, is a perceptual scale of pitches judged by listeners to be equal in distance from one another. The reference point between this scale and normal frequency measurement is defined by assigning a perceptual pitch of 1000 mels to a 1000 Hz tone, 40 db above the listener 's threshold. above about 500 Hz increasingly large intervals are judged by listeners to produce equal pitch increments. As a result, four octaves on the hertz scale above 500 Hz are judged to comprise about two octaves on the mel scale The name mel comes from the word melody to indicate that the scale is based on pitch comparisons Feature extraction v 9a
Mel scale (Melody scale) From https://en.wikipedia.org/wiki/Mel_scale • Measure relative strength in perception of different frequencies. • The melscale, named by Stevens, Volkmann, and Newman in 1937,[1] is a perceptual scale of pitches judged by listeners to be equal in distance from one another. The reference point between this scale and normal frequency measurement is defined by assigning a perceptual pitch of 1000 mels to a 1000 Hz tone, 40 dB above the listener's threshold. Above about 500 Hz, increasingly large intervals are judged by listeners to produce equal pitch increments. As a result, four octaves on the hertz scale above 500 Hz are judged to comprise about two octaves on the mel scale. The name mel comes from the word melody to indicate that the scale is based on pitch comparisons. Feature extraction, v.9a 12
Critical band scale: mel scale Based on perceptual studies Scale Log scale when freq Is above Am=150: 2m 1KHZ Linear scale when freq is below 1 KHZ Popular scales are the"Mel (stands for melody or"Bark scales 4 m=2595k0 801+ 700 ()Freq in hzu: Af=7000-6000 Feature extraction v 9 Below1KHz,△f≈△m, linear http://en.wikipedia.org/wiki/melscaleAbove1kHz,Af>am,logscale
Critical band scale: Mel scale • Based on perceptual studies – Log. scale when freq. is above 1KHz – Linear scale when freq. is below 1KHz • Popular scales are the “Mel” (stands for melody) or “Bark” scales = + 700 2595log1 0 1 f m Feature extraction, v.9a 13 (f) Freq in hz Mel Scale (m) http://en.wikipedia.org/wiki/Mel_scale m=150 f=7000-6000 Below 1KHz, fm, linear Above 1KHz, f>m, log scale
Exercise 3.0: Exercise(i): When the input frequency ranges from 200 to 800 Hz Af=600Hz), what is the delta Mel (am)in the mel scale? Exercise): When the input frequency ranges from 6000 to 7000 Hz(Af=1000Hz), what is the delta mel (am in the mel scale? Feature extraction v 9a
Exercise 3.0: • Exercise (i): When the input frequency ranges from 200 to 800 Hz (f=600Hz), what is the delta Mel (m) in the Mel scale? • Exercise (ii): When the input frequency ranges from 6000 to 7000 Hz (f=1000Hz), what is the delta Mel (m) in the Mel scale? Feature extraction, v.9a 14
Matlab program to plot the mel scale Matlab code File Edit View Insert Iools Desktop Window %plot mel scale f=1: 10000 %input frequency range Plot of Frequency to Mel scale 3500 mel=2595*og10(1+f/700) figure(1) 300- ·cf olot(f, mel) 2000-…1-1-1 grid on xlabel( freqeuncy in HZ) g1500 ylabel( freqeuncy mel scale 100 title( plot of Frequency to mel cale 0100020003000 500060007008000900010000 in HZ Feature ext
Matlab program to plot the mel scale Matlab code • %plot mel scale, • f=1:10000 %input frequency range • mel=(2595* log10(1+f/700)); • figure(1) • clf • plot(f,mel) • grid on • xlabel('freqeuncy in HZ') • ylabel('freqeuncy Mel scale') • title('Plot of Frequency to Mel scale') Plot • Feature extraction, v.9a 15