Created by Simon and Kadie
about 11 years ago
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A sound that humans can listen to is an Analogue sound
A sound processed by a computer is in digital form
Sampling
The sampling rate (frequency) is the number of samples per seconds per, measured in Hz
The sampling resolution is the number of bits given to each sample, more bits - more accurary
The highest representation of sound happens with the highest samping rate and the largest samping resolution
This presents two issues:-Storage space will need to be larger-Bandwidth needed to transmit the signals will be larger
Sampling sound at 20kHz for 1 minute will produce 10,000 x 60 = 600,00 samplesWith a sampling resolution of 4 bits, a minute will need 600,00 x 4 = 2,400,00 bits, in bytes = 300,00 bytes, which in kbytes = 300 kbytes
Nyquist's Theorem
Sample at a frequency at least twice the rate of the higest fregwncy in the sampled sound to avoid missing detail in the original signal
Human hearing = 20Hz to 20,00HzCd recording frequency must be sampled at 40,000HzThis will produce 20,000Hz signal, sound for a CD is sampled at 44.1kHz
Steaming Audio
Instead of downloading the whole file, data is sent part by part playing the sound when it has enough to play.
Streamed data is buffered on arrival and played while the buffer is not empty. If thbuffer empties then the playing program normally paused until there is enough in the buffer.
Streaming means that large files do not need to be transferred in one go and it reduced the ease with whih files can be copied.
Editing Sound
-Further sound can be added-The 'shape' of the sound can be changed' -the pitch and duration can also be altered-Sound can be processed to add effects, like the addition of sounds to make the sound appear to come from a concert hall or a room with an echo-Stereo tracks can be sepearted out
Sound Formats
WAV - large amount of space, uncompressedMP3 - compact sound file, removed frequencies outside the human range and compressed the resulting signalMIDI - Musical Infomation Digital Interface, Format that stores the pitch, duration and instrument, very compact, allows editing
Analogue + Digital
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