height=32.1099992752075 /> and have a length of. The construction of Daubechies orthogonal wavelets begins by choosing the number of zeros p at. The zeros the filters associated with the db6 are depicted in Figure 7. Here, we also need to choose the binomial polynomial associated with it which has a degree of The coefficients of these polynomials can be found recursively for p by using the following equation:
For a given value p, the coefficients of are in an ascending order . To get the roots of, one scales b by 4 and to facilitate the numerical calculations, one uses the variable 4y instead of y. The ratio of any two consecutive coefficients is:
Which in its simplest form can be expressed as:
This equation will be used in Section 5 to construct the family of polynomials with coefficients equal to the ratios of this polynomial consecutive coefficients.
Now to compute the zeros of other than −1, we note that according to [1,9] the frequency response of the half-band filter is given by:
Figure 7. Zeros of B(y) for db6.
On the unit circle we have:
Also, off the unit circle we use the same relation between z and y. Rearranging these terms leads to:
Now let and then,
with, this implies that:
are the two roots of for each root y of.
That is, we have roots and their inverses, namely:
The distribution of these zeros in the plane is shown in Figure 8. From, is then derived and all is left is to factorize. Daubechies did the following factorization found in :
where is a polynomial of degree.
The Construction of db6
For p = 6, the db6 wavelet is obtained. Figure 8 shows the location in the complex plane for the zeros of associated with the Daubechies db6 orthogonal wavelet. The frequency responses of the analysis lowpass filter and synthesis lowpass filter of this wavelet are depicted in Figure 9. Therefore completing the construction of the scaling function along with the mother wavelet. The decomposition and reconstruction functions for the mother wavelet db6 are plotted in Figure 9, while Figure 10 shows the impulse response of the four filters associated with it.
Now, given the coefficients of the low-pass filter, it is shown in [1,7] that the coefficients of the filters, and that
Figure 8. Zeros of P(z) for db6 and the frequency responses of the filters P, H0 and H1.
Figure 9. The db6 analysis and synthesis scaling and wavelet functions.
lead to orthogonality can be derived from the coefficients of as follows:
First, the coefficients of the high-pass filter of the analysis bank are obtained from those of the low-pass filter by the “alternating flip”.
This can be represented by three operations on the coefficients of.
1) Reverse the order;
2) Alternate the signs;
3) Shift by an odd number l.
This takes the low-pass filter coefficients into an orthogonal high-pass filter  which is represented in the
Figure 10. Impulse response for the reconstruction and decomposition filters of db6.
Then, the coefficients of the high-pass filter of the synthesis bank are obtained by the reverse of the coefficients of the high-pass filter of the analysis bank. They can be generated by the following equation:
The coefficients of the low-pass filter of the synthesis bank are the alternating flip of the coefficients of. They can be generated by the following equation:
where l is the length of the low-pass filter .
The scaling and wavelet functions are then derived from the coefficients of these filters. The scaling function satisfies the equation :
where, is the reverse of and the wavelet function is then derived from the scaling function by the equation:
4. Zeros of Ratio Coefficients Polynomials
Now we consider the class of polynomials with coefficients those of the ratios obtained in Equation (4). An optimal limit of these zeros in the complex plane was presented in . Other theorems and alternative approach to proving this distribution can be found in . Now the rations can be expressed as follows:
We note that these coefficients are in an ascending order where.
Theorem I: The roots of the polynomials lie inside the unit disk for all p.
Proof: For, consider
For, we have:
Replacing z with, we get:
Hence, if (i.e.), then:
The Distributions of Zeros for db6
For the Daubechies wavelet “db6” this polynomial is:
with maximum module of 0.9325. The roots of this polynomial are depicted below in Figure 11 and observed to reside all in the unit circle.
5. The Construction of db8 The scaling and wavelet functions are then derived from the coefficients of these filters. They satisfy respectively the equations :
To compute the 14 zeros of other than −1, note that on and off the unit circle we have the following relation between z and y:. This implies that the equation:
The coefficients of are displayed in Table 2.
If one sets and then, z = x + u and are the two roots of for each root y of. Note that. That is, we have 7 roots and their inverses, The plot of these zeros in the plane are shown in Figure 12. Also, the values of, and are listed in Table 3.
From the definition of, is obtained and all is left now is to factorize. Were is a polynomial of degree 14 and chosen to satisfy Equation 16. It is equal to. The different factorizations of into lead to different mother wavelets. Choosing to have its seven zeros inside the unit circle and to have its seven zeros outside the unit circle leads to the Daubechies orthogonal mother wavelet db8.
The scaling and wavelet functions of one of the Daubechies wavelets’ family member called db8 are shown in Figure 13. The same figure also shows the impulse response of the four filters associated with that wavelet and Table 4 displays The coefficients of the of db8 filters.
Figure 11. Zeros of Q4(z) for Daubechies db6 orthogonal wavelet.
Table 2. The coefficients of the polynomial B8(y).
Table 3. The roots of Q14(z) inside the unit circle z = x – u and outside of it z = x + u.
Table 4. The coefficients of the of db8 filters.
To carry out the factorization we note that has 16 roots at and 14 other roots which occur in pairs (z and). This means that we have 7 roots inside the unit circle and the other 7 roots outside the unit circle. The roots inside the circle are the roots for the filter coming from the equation: and the ones outside it are for filter obtained from the equation:. These roots when factorized lead to the coefficients of these two filters and they are shown in Table 3 for. The coefficients of the high-pass filters and are simply then derived from the low-pass filter coefficients by the alternating sign property.
The scaling and wavelet functions of one of the
Figure 12. Zeros of P(z) for db8 and the frequency responses of the filters: P0, H0 and H1.
Daubechies wavelets’ family member called db8 are shown in Figure 13. The same figure also shows the impulse response of the four filters associated with that wavelet.
The general characteristics of this wavelet include compact support for which exact reconstruction are possible with FIR filters. Its associated scaling filter is a minimum-phase filter. This wavelet is a member of the orthogonal set of wavelets that are usually denoted by: N represents the order of the reconstruction and decomposition wavelet. Their corresponding filter length is.
In this paper we construct Daubechies orthogonal wavelets via the two channel perfect reconstruction filter bank. The cases of db6 and db8 are examined where we derived the coefficients of the filters associated with these wavelets and the roots of the binomial polynomials that made this construction possible. The locations of the zeros of the polynomials involved in this construction were found and their locations were discussed. The distribution of the zeros of a family of polynomials having their coefficients as the ratios of those of the binomial polynomials was examined and were proved to reside inside the unit circle. Similar discussions about the Daubechies Biorthogonal wavelets family are included along with the constructions of Bior3.5, Bior3.9 and Bior6.8.
The author would like to thank Alfaisal University and its Office of Research for securing the time, environment and funds to complete this research project. This work
Figure 13. db8 Wavelet and scaling functions. The impulse response for the reconstruction and decomposition filters of the wavelet db8.
was also supported by the Alfaisal University Start-Up Fund (No. 410111410091).
*Dedication: This paper is dedicated to my professors and supervisors Karl Dilcher and William Phillips.