Lecture # 22 Audition, Audacity & Sound Editing

Lecture # 22 Audition, Audacity & Sound Editing

Sound Representation

Sound waves through Air Voltage converted to numbers Different Voltages Digitizing Sound

Physics of Sound

Physics of Sound • Amplitude increases sound gets louder • Loudness measured in decibels (dB) - dB = 20 * log10(Amplitude/Reference Amplitude) - 2 x loudness => 10 x amplitude - 6 dB ~ smallest perceptible difference in amplitude - Speakers go from 50 to 100 watts => ~ 6 dB increase

Common dB Levels • Decibel scale: smallest audible sound (~ total silence) is 0 dB. • Near total silence – 0 dB • Breathing – 10 dB • A whisper – 15 dB • Mosquito – 20 dB • Normal conversation – 60 dB • Over time, can damage hearing – 85 dB • A lawnmower – 90 dB • A car horn – 110 dB • A rock concert or a jet engine – 120 dB • Pain – 130 dB • A gunshot or firecracker – 140 dB

Decibel Exposure Time Guidelines Accepted standards for recommended permissible exposure time for continuous time weighted average noise, according to NIOSH and CDC, 2002. For every 3 dBs over 85dB, the permissible exposure time before possible damage can occur is cut in half. 85 dB 8 hours 88 dB 4 hours 91 dB 2 hours 94 db1 hour 97 db30 minutes 100 db15 minutes 103 db7.5 minutes 106 dB 3.75 min (< 4min) 109 dB 1.875 min (< 2min) 112 dB 56 seconds 115 dB 28 seconds 118 dB 14 seconds 121 dB 7 seconds 124 dB 3.5 seconds 127 dB 1.75 seconds 130 dB Almost immediately In other words, be careful or you will go deaf!

Frequency • Cycles per second or wavelength • Measured in Hz (Hertz) • Wavelength = Speed of sound through air/Hz • The higher the Hz the higher the pitch • Lowest Pitch – About 15 Hz • Highest Pitch – Approximately 20 kHz • Logarithmic in perception

Tone Test • What range of frequencies can you hear? • Can you hear a 440 Hz Sinusoid? • 880 Hz? • 1760 Hz? • 3520 Hz? . . - 10000 Hz?

Audacity & Audition • Download: http://audacity.sourceforge.net/ • Loading and Saving/Exporting Files • Mute/Solo/Volume • Select/Cut/Paste • Zoom • Multi-track/Stereo

Sinusoidal Tone Demo in Audacity Generate > Tone 880 Hz Frequency 440 Hz 1620 Hz 220 Hz 3240 Hz 160 Hz 6480 Hz 120 Hz How low can you go? How high can you go?

A sound wave one half as many samples one quarter as many samples Sampling Frequency • How often do we measure the voltage?

Sampling Frequency Base Sampling Frequency 127 127 127 0 0 0 0 0 0 0 -127 -127 -127 Array Representation

Sampling Frequency Twice Base Sampling Frequency 127 127 127 90 90 90 90 90 90 0 0 0 0 0 0 0 -90 -90 -90 -90 -90 -90 -127 -127 -127 Array Representation Nyquist Theorem

Sampling frequency • Like resolution in images • More samples = better quality • Fewer samples = less space

Sampling Frequencies • People talking on the phone • 10 KHz • 10 KiloHertz • 10,000 samples per second • CD quality music • Highest frequency: 22 KHz (44.1 KHz Sampling rate) • Stereo • Two different signals, two different arrays

Quantization • How many bits per sample Sound Wave Heavily Quantized

Quantization 7 3 1 6 5 2 4 3 1 2 0 1 0 0 -1 -1 -2 -3 -1 -4 -2 -5 -6 -3 -7 -8 -4 -2 Bits Per Sample: Speech – 8 bits (1 byte) CD Music – 16 bits (2 bytes) Professional Quality – 32 bits (4 bytes)

Dynamic Range 3 3 3 2 2 2 1 1 1 0 0 0 -1 -1 -1 -2 -2 -2 -3 -3 -3 -4 -4 -4

Quantization • Speech • 8 Bits per sample • CD Music • 16 Bits per sample • Professional quality • 32 Bits per sample

Representing Sound • An array of amplitudes (voltage measurements) • Sampling Frequency • Quantization • Dynamic Range

Dynamic Range • How loud of a noise can you record Dynamic range Exceeding dynamic range

Where are the Words? Jane loves the knows Fred (Phred) dog Ralph

Jane Fred loves A “sound font” dog loves Fred the Jane Ralph knows

Sound Review • The physics: pressure, waves, db • Frequency and Sampling • Quantization and Fidelity • Dynamic Range

Lecture # 22 Audition, Audacity & Sound Editing