- Rectangular, Blackman, Hamming, Dolph-Chebychev, etc.. - Which algorithms? - Rectangular: inluded for preliminary testing) - Blackman: used to compare and contrast with hamming - Hamming: a useful and very good algorithm. this provides nice side lobe attenuation - Dolph-Chebyshev: another very good algorithm. This possesses a frequency response similar to a Hamming window, however provides better attenuation of high frequencies. the minumum attenuation of frequencies greater than the sampling frequency for dolph-chebyshev is 63 dB as compared to 50 dB for hamming - Assess alternative algorithms This has been designed to be easily extensible. A new algorithm can be added by specialising the cepWindowAlg class and overriding the getValue method. A new windowing algorithm can be added at the expense of less than 10 lines of code (with the exception of those such as dolph-chebyshev who require alot more attention) - How was it done? cepWindowAlg <------------------- cepDataWindower ^ | -------------------------------------- | | | | rectangular blackman hamming chebyshev - These coefficients can be generated for an arbitrary window size. The requirement that the windowed data can be converted to the Fourier domain imposes afuther limitation in that the fourier libraries we are using will only operate on a data set of size 2^n ( 0 < n < inf); This restriction has been implmented at the UI level, maintaining the flexibility of the windowing subsystem. - Blackman - this was added at a simlar time coeff(i) = 0.42 - 0.5*cos( 2*PI*val ) + 0.08*cos(4*PI* i/(size-1)); - Hamming. implemented using the time honoured formula coeff(i) = 0.54 - 0.46*cos( 2*PI*i/(size-1) ); - Dolph-Chebychev http://www.maths.tcd.ie/~plynch/Publications/Dolph.pdf http://www.isip.msstate.edu/projects/speech/software/documentation/class/algo/Window/ http://www.octave.org/octave-lists/archive/octave-sources.2002/msg00019.html dolph - etc.. - Speed/ Optimisations - calulation of window coefficients are performed only when the algorithm is changed, or paramters are altered. - for the simpler algoritms, speed is not an issue. Th emost expensive of these algorithms [blackman] 2 cosines and 6 muliplications. this is inexpensive when considering the frequency at which recalulation will be required, and the relatively small size of the window required. - Dolph-Chebyshev will be more expensive. The code that is implmented is based on a FORTRAN algorithm. This has been implmented as faithfully as possible so as to maintain the integrity of the window coefficients. The support the ability of the user to request a window of arbitrary size, this particular window algorithm implements is own inverse fourier transform. - possibility of adding more windowing algorthms - possible optimisation of the dolph-chebyshev code