Lecture # 22 Audition, Audacity & Sound Editing

Sound Representation

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

Physics of Sound

Amplitude increases sound gets louder Loudness measured in decibels (dB) - dB = 20 * log 10 (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, For every 3 dBs over 85dB, the permissible exposure time before possible damage can occur is cut in half. 109 dB1.875 min (< 2min) 112 dB56 seconds 115 dB28 seconds 118 dB14 seconds 121 dB7 seconds 124 dB3.5 seconds 127 dB1.75 seconds 130 dBAlmost immediately 85 dB8 hours 88 dB4 hours 91 dB2 hours 94 db1 hour 97 db30 minutes 100 db15 minutes 103 db7.5 minutes 106 dB3.75 min (< 4min) 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? Hz?

Audacity & Audition Download: Loading and Saving/Exporting Files Mute/Solo/Volume Select/Cut/Paste Zoom Multi-track/Stereo

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

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

Sampling Frequency Base Sampling Frequency Array Representation

Sampling Frequency Twice Base Sampling Frequency Nyquist Theorem Array Representation

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 Bits Per Sample: Speech – 8 bits (1 byte) CD Music– 16 bits (2 bytes) Professional Quality – 32 bits (4 bytes)

Dynamic Range

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? Janelovesthe dogRalph knowsFred (Phred)

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

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