Modal synthesis technique

In prior chapters we looked at subtractive synthesis techniques, such as modal synthesis (Chapter 4) and linear predictive coding (Chapter 8). In these methods a complex source is used to excite resonant fQters. The source usually has a flat spectnun, or exhibits a simple roll-off pattern like f or ip (6 dB or 12 dB per octave). The filters, possibly time-varying, shape the spectrum to model the desired sound. 

Another very useful technique that alleviates some of the aforementioned difficulties is the controlled double-jet precipitation (CDJP) process, which can be extended to a triple jet design. The technique was originally developed to produce uniform large particles (23-25), particularly of silver halides for photographic applications. Recently, it was demonstrated that the procedure may be used for the synthesis of a variety of uniform dispersions, including those of metal oxides of different modal sizes, ranging from several nanometers to several micrometers (26-29). 

Lu and Yeh [174] record an emulsion technique for the synthesis of ZnO. They dissolved zinc acetate in de-ionized water to obtain the aqueous phase, n-heptane was used as the continuous phase, in which a surfactant (Span 80) was added. The two phases in different proportions were mixed continuously for Ih for obtaining homogeneous emulsions. Ammonium hydroxide was added into the emulsions to cause precipitation of zinc. The precipitates were dried and calcined at 700 -1000°C/2 h, which yielded white powders of ZnO. The modal particle size was 0.080 pm, while the mean size was about 0.08-0.09 pm depending on experimental conditions. 

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