Russell Taylor

How Sound Works Sound “source” creates variations in air pressure Main source output is Speakers Use vibrating cones which mimic the signal strength received from the sound signal generator e.g. The radio circuitry, PC Sound card, HiFi / Deck sound circuitry, etc. Differences in air pressure from Speakers are received by users ears, as air is pushed back and forth from the Speaker cone The further away from the speaker the lower the volume The effects of the air being pushed recedes the further the air is from the source – similar to the way waves work

Sound Systems Mono – short for Monophonic or single channel sound Least sophisticated sound type Stereo – short for stereophonic or dual channel Two separate channels can record different sounds or blend sources across channels to provide effect of movement E.g. Can record the Doppler Shift / Effect

Components of Sound Amplitude volume Frequency how often amplitude changes Harmonic content “richness” of sound – how many components of sound

Frequency Measured in complete cycles per second called Hertz (Hz) (see page 175) 1 Hz equals 1 complete cycle per second Human ear can detect from 20Hz to 20kHz, but most can hear from 100Hz to 17kHz (17,000 Hz) – age reduces range of hearing and sensitivity Animals can detect a wider range than humans Voices produce sounds ranging from 40Hz to 4kHz (4000Hz) Music can span the whole range of human hearing

Frequency Spectrum DescriptionRangeTypical Use Sub-audioUp to 20HzBelow hearing range Audio20Hz to 20kHzHuman range Ultrasonic devices20kHz to 30kHz‘Silent’ dog whistles, some remote control devices Long wave30kHz to 300kHzRadio Medium wave300kHz to 3MHzRadio Short wave3MHz to 30MHzRadio VHF30MHz to 300MHzRadio / Old TV standard UHF300MHz to 3GHzTV, aircraft landing systems Microwaves3GHz and aboveRadar, satellites, TV & Comms. links

Frequency Scales The bottom waves have higher frequencies than those above. The horizontal axis represents time

Amplitude Two main meanings: Volume / Intensity to the human ear – sound pressure Changing signal level in a device such as a sound card or amplifier Measured in “Decibels” – dB Not a linear scale A logarithmic scale Double = 3dB 4 x volume = 6dB See page 176

Decibel levels dB LevelsExample 160Jet engine 130Large orchestra at full blast 120Start of pain threshold 100Loud rock music 90Underground 80Car / Lorry 70Normal conversation 40Quiet conversation 30Whisper 10Background noise in recording studio 0Hearing threshold

Wavelength Distance from one peak of a wave to the next. Wavelength is measured in units of distance – newton metres - nm

Wavelengths

Waveforms

Harmonics Sounds made from “elements” – the “sonic signature” These elements are different from the basic frequency of the notes emitted These elements are sounds similar to but different from the pure sound (see graphics on age 177)

Using Sound in Applications To inform users Essential information – facts & figures To influence attitudes Using specific voices – child, elderly, politician, actor, tone or regional accent To create atmosphere - using sound to reinforce screen content Scary, happy, sad, etc. avis_butthead_laugh.wav avis_butthead_laugh.wav

Exercise Log on to: effects/ effects/ Browse these sound sources looking for relevant sounds for your project Download sounds as required to your “My Digital Media Project” folder

Have Some Fun