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A Gauss-Chebyshev, or transitionally Gaussian filter combines the
advantages of both the Gaussian
and the Chebyshev response. For low frequencies, the response is
approximately Gaussian, which results in a good phase linearity.
Above a certain frequency, the transition frequency, the response becomes
more like a Chebyshev response, which means good damping.
The command to generate such a filter is

`tgauss ( `
`<`*order*`>`
`, `
`<`*ripple*`>`
`, `
`<`*damping*`>`
`) ;`

and
results in a transitional Gaussian filter with specified order and
ripple in dB, up to a specified damping in dB. For instance
`tgauss(4, 0.01, 6);` results in a filter which is Gaussian to
6dB with 0.01dB ripple. To keep the group delay
reasonably constant, the ripple should be small,
most often between 0.001dB and 0.01dB.

2009-06-03