Comments on Finite Impulse Response Filters The central charge that is leveled in Roark's (1997)  critique is that the finite impulse response (FIR) filtering technique that we described does not, in fact, enable the construction of filters with arbitrary amplitude and phase responses, as we claimed. Roark states that this is impossible because “...the phase ... Letter to the Editor
Letter to the Editor  |   April 01, 1997
Comments on Finite Impulse Response Filters
 
Author Affiliations & Notes
  • James Hillenbrand
    Western Michigan University Kalamazoo
  • Robert A. Houde
    RIT Research Corporation Rochester, New York
Article Information
Hearing & Speech Perception / Research Issues, Methods & Evidence-Based Practice / Speech / Letters to the Editor
Letter to the Editor   |   April 01, 1997
Comments on Finite Impulse Response Filters
Journal of Speech, Language, and Hearing Research, April 1997, Vol. 40, 408-409. doi:10.1044/jslhr.4002.408
History: Received November 7, 1996 , Accepted November 14, 1996
 
Journal of Speech, Language, and Hearing Research, April 1997, Vol. 40, 408-409. doi:10.1044/jslhr.4002.408
History: Received November 7, 1996; Accepted November 14, 1996
The central charge that is leveled in Roark's (1997)  critique is that the finite impulse response (FIR) filtering technique that we described does not, in fact, enable the construction of filters with arbitrary amplitude and phase responses, as we claimed. Roark states that this is impossible because “...the phase response of all FIR filters is linear, with control only over the rate of phase in the frequency response...” and, as a consequence, the “...phase response of FIR filters is therefore specified by a single parameter, resulting in a filter delay that is constant for all frequencies...” (p. 405). The author is quite right that a constraint of this kind would be inconsistent with our description of this technique as enabling the construction of filters whose responses at the sample frequencies can be arbitrary amplitude and phase functions. However, the assertion that this design constraint applies to FIR filters is simply not true. A point that is made in nearly every elementary text on digital filtering is that FIR filters have the desirable property of permitting a linear phase design, not requiring it. For example, as Jackson (1986)  notes on this type of filter, “...their most important property...[is]...that the coefficients of a FIR filter are easily constrained to produce a linear phase response...” (p. 56, emphasis added). The key word in this citation is constrained: Claiming that a filter can have a linear phase response is hardly equivalent to claiming that the filter must have a linear phase response. It is, in fact, very difficult to see where a linear-phase constraint might arise since, as we point out in our paper, the method of constructing the impulse response is a direct implementation of the inverse discrete Fourier transform (DFT). There are no restrictions inherent in the DFT that would preclude nonlinear phase spectra.
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