1. 3rd practice Medical Informatics Biomedical Signal Processing TAMUS, Zoltán Ádám zoltanadam_tamus@yahoo.com

2.  Signal processing Input device A/D converter Conputer processing, storing D/A converter Output device Electrical signal Binary number

3.  Sound, biological signal (function of time) Sampling Quantization

4.  Problem: Losing information in the interval between samples!  Nyquist-Shannon theorem: f s >2f, 2T s <T f s : sampling frequency  Aliasing: when the Nyquist-Shannon equation is not satisfied Movie: the wheel rotate „contrariwise”

5.  Ordering numbers to samples Nearest value

6.  Quantization Problem: losing of the values between steps

7.  The difference between the original and the recovered signal is the quantization noise

8.  Important: The useful part of signal is not covered by noise  Signal to Noise Ratio (SNR)  SNR=6,08n+1,78 [dB] n: the number of bits of the converter („the resolution of the amplitude axis”)

9.  Frequency range Shannon theory  Dynamic Range Signal-to-Noise Ratio

10.  The sound is a mechanical wave which is generated by a vibrating object and propagated through a medium.  The propagation method of the sound is longitudinal wave because the motion of individual particles of the medium is parallel with the energy transfer direction of the wave.

11.  Main properties: Frequency  0-20 Hz: Infrasound  20 Hz-20 kHz: Sound  20 kHz-1 GHz: Ultrasound  1 GHz- 10 THz: Hypersound Sound pressure  Deviation from local ambient pressure [p; unit: Pa] Intensity  Sound power per unit area [I; unit W/m 2 ]

12.  Sound Intensity Level [L I unit: dB]: I 0 =10 -12 W/m 2  Sound Pressure Level [L P unit: dB]: p 0 = 20 μ Pa

13. SourceIntensityIntensityLevel # Times Greater Than TOH Threshold of Hearing (TOH) 1*10 -12 W/m 2 0 dB10 0 Rustling Leaves1*10 -11 W/m 2 10 dB10 1 Whisper1*10 -10 W/m 2 20 dB10 2 Normal Conversation1*10 -6 W/m 2 60 dB10 6 Busy Street Traffic1*10 -5 W/m 2 70 dB10 7 Vacuum Cleaner1*10 -4 W/m 2 80 dB10 8 Large Orchestra6.3*10 -3 W/m 2 98 dB10 9.8 Walkman at Maximum Level 1*10 -2 W/m 2 100 dB10 Front Rows of Rock Concert 1*10 -1 W/m 2 110 dB10 11 Threshold of Pain1*10 1 W/m 2 130 dB10 13 Military Jet Takeoff1*10 2 W/m 2 140 dB10 14 Instant Perforation of Eardrum 1*10 4 W/m 2 160 dB10 16

14.  Fletcher-Munson curves

15.  Using an audio processor program software: Audacity http://audacity.sourceforge.net/http://audacity.sourceforge.net/