06_CM0340_Synthesis

06_CM0340_Synthesis - 173 JJ II J I Back Close Some...

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Unformatted text preview: 173 JJ II J I Back Close Some Practical Multimedia Digital Audio Applications Having considered the background theory to digital audio processing, lets consider some practical multimedia related examples: Digital Audio Synthesis making some sounds Related : Digital Audio Effects changing sounds via some standard effects ( See CM0268 ). MIDI synthesis and effect control and compression 174 JJ II J I Back Close Digital Audio Synthesis We have talked a lot about synthesising sounds. Several Approaches: Subtractive synthesis FM (Frequency Modulation) Synthesis Additive synthesis Sample-based synthesis Wavetable synthesis Granular Synthesis Physical Modelling 175 JJ II J I Back Close Subtractive Synthesis Basic Idea : Subtractive synthesis is a method of subtracting overtones from a sound via sound synthesis, characterised by the application of an audio filter to an audio signal. First Example: Vocoder talking robot (1939). Popularised with Moog Synthesisers 1960-1970s 176 JJ II J I Back Close Subtractive synthesis: Simple Example Simulating a bowed string Take the output of a sawtooth generator Use a low-pass filter to dampen its higher partials generates a more natural approximation of a bowed string instrument than using a sawtooth generator alone. 2 4 6 8 10 12 14 16 18 20 0.5 0.4 0.3 0.2 0.1 0.1 0.2 0.3 0.4 0.5 2 4 6 8 10 12 14 16 18 20 0.4 0.3 0.2 0.1 0.1 0.2 0.3 subtract synth.m MATLAB Code Example Here. 177 JJ II J I Back Close Subtractive Synthesis: A Human Example We can regard the how humans make noises as subtractive synthesis: Oscillator the vocal cords act as the sound source and Filter the mouth and throat modify the sound. Saying or singing ooh and aah (at the same pitch.) Vocal chords are generating pretty much the same raw, rich in harmonic sound Difference between the two comes from the filtering which we apply with the mouth and throat. Change of mouth shape varies the cutoff frequency of the filter, so removing (subtracting) some of the harmonics. The aah sound has most of the original harmonics still present, The ooh sound has most of them removed (or to be more precise, reduced in amplitude.) 178 JJ II J I Back Close Subtractive Synthesis: Another Human Example A sweeping filter oohs to aahs again By gradually changing from ooh to aah and back again simulate the sweeping filter effect Effect widely used in electronic music Basis of the wahwah guitar effect, so named for obvious reasons. We will see how we produce this effect in MATLAB code shortly. 179 JJ II J I Back Close Subtractive Synthesis: One More Human Example Making Aeroplane Noise Make a ssh sound white noise Now synthesise a jet plane landing sound Should mostly by use mouth shape to filter the white noise into pink noise by removing the higher frequencies.pink noise by removing the higher frequencies....
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06_CM0340_Synthesis - 173 JJ II J I Back Close Some...

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