ENG 006 Notes-- began 2-11

ENG 006 Notes-- began 2-11 - Notes SOUND IMAGE Processing...

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Notes 2/11/11 amplitude - loudness higher frequency - sharper signals (vice versa) Sampling Theorem to convert an analog wave form to number, we have to measure the waave form at several intervals of time: this is done through SAMPLING try to remake the original sample you can decompose any analog wave back to a SINUSOID wave Sampling Theorem States that perfect reconstruction of a signal is possible when the sampling frequency is greater than twice the maximum frequency of the signal being sampled. If lower sampling rates are used, the original signal's information may not be completely recoverable from the sampled signal. For example, if a signal has a upper band limit of 100Hz, a sampling frequency greater that 200 Hz will avoid ALIASING and allow theoretically perfect recontruction. aliasing is similar to watching a wagon moving forward, but the wheels "look" like they are going in reverse (while watching tv) Human Ear The full range of human hearing is between 20Hz and 20kHz the minimum sampling rate that satisfies the Sampling Theorem for this full BANDWIDTH is 40kHz. The 44.1 kHz sampling rate used for Compact disc was chosen or this and other technical reasons. Example of Rates 8000 Hz: telephone, walkie-talkie 44,100: MPEG - 1, MP3, audio CD Representing Sound
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all amplitude values are stored in a vector Hertz - means cycle per second use linspace command to equally space out points We then give the vector of the amplitudes of the samples and out sampling rate to a function called AUDIOPLAYER, which returns on an 'AUDIOPLAYER OBJECT' that we store in the variable p. Now, we can play (p) or stop(p). Read/Store Audio Files of course, playing single notes is kind of boring. We can import sound into MATLAB using the wavread(. ..) function, passing it just the file name of a wave file To read ansd store an audio file, you can use one of two different command lines. The following stores the file into variable y. >>y = wavread('filename'); Remember to include the entire filename Audio Playback To play an audio file in MatLab you use the sound(. ..) function. The following funtion plays the sound. If the Fs Audio Scaling To scale an audio file to the soundsc(. ..) command is used. This allows for the modification of audio signal's amplitude or frequency. Playing Backwards
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This note was uploaded on 03/10/2011 for the course GEOGRAPHY 101 taught by Professor Lee during the Spring '11 term at American River.

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ENG 006 Notes-- began 2-11 - Notes SOUND IMAGE Processing...

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