Realizable warped IIR filters and their properties

Karjalainen, Matti; Härmä, Aki; Laine, Unto K.

doi:10.1109/icassp.1997.599488

Cited by 17 publications

(13 citation statements)

References 7 publications

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“…Frequency warping can be used to design both finiteimpulse response (FIR) and infinite-impulse response (IIR) filters (Karjalainen et al [10]). A frequency-warped FIR filter, for example, can be designed by replacing the unit delays in the conventional FIR filter with all-pass filter sections.…”

Section: Frequency Resolutionmentioning

confidence: 99%

Multichannel Dynamic-Range Compression Using Digital Frequency Warping

Kates

Arehart

2005

EURASIP J. Adv. Signal Process.

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A multichannel dynamic-range compressor system using digital frequency warping is described. A frequency-warped filter is realized by replacing the filter unit delays with all-pass filters. The appropriate design of the frequency warping gives a nonuniform frequency representation very close to the auditory Bark scale. The warped compressor is shown to have substantially reduced group delay in comparison with a conventional design having comparable frequency resolution. The warped compressor, however, has more delay at low than at high frequencies, which can lead to perceptible changes in the signal. The detection threshold for the compressor group delay was determined as a function of the number of all-pass filter sections in cascade needed for a detectible change in signal quality. The test signals included clicks, vowels, and speech, and results are presented for both normal-hearing and hearing-impaired subjects. Thresholds for clicks are lower than thresholds for vowels, and hearing-impaired subjects have higher thresholds than normal-hearing listeners. A frequency-warped compressor using a cascade of 31 all-pass filter sections offers a combination of low overall delay, good frequency resolution, and imperceptible frequency-dependent delay effects for most listening conditions

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Section: Frequency Resolutionmentioning

confidence: 99%

Multichannel Dynamic-Range Compression Using Digital Frequency Warping

Kates

Arehart

2005

EURASIP J. Adv. Signal Process.

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“…It follows that hinged stiff systems are only described by (42). In this equation, sinh(ξ 2 L) = 0 has no solution, hence the eigenfrequencies are determined by the condition…”

Section: Hinged Stiff String and Rodmentioning

confidence: 98%

“…Note, that the feedback all-pass chain results in delay-free loops. Computationally, these loops can be resolved by the methods illustrated in [34,42,43]. Moreover, the phase response of the loop filter G(z) contributes to the dispersion and it must be taken into account in the global model.…”

Section: Numerical Approximations Of Stiff Systemsmentioning

confidence: 99%

Physically Inspired Models for the Synthesis of Stiff Strings with Dispersive Waveguides

Testa

Evangelista

Cavaliere

2004

EURASIP J. Adv. Signal Process.

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We review the derivation and design of digital waveguides from physical models of stiff systems, useful for the synthesis of sounds from strings, rods, and similar objects. A transform method approach is proposed to solve the classic fourth-order equations of stiff systems in order to reduce it to two second-order equations. By introducing scattering boundary matrices, the eigenfrequencies are determined and their n2 dependency is discussed for the clamped, hinged, and intermediate cases. On the basis of the frequency-domain physical model, the numerical discretization is carried out, showing how the insertion of an all-pass delay line generalizes the Karplus-Strong algorithm for the synthesis of ideally flexible vibrating strings. Knowing the physical parameters, the synthesis can proceed using the generalized structure. Another point of view is offered by Laguerre expansions and frequency warping, which are introduced in order to show that a stiff system can be treated as a nonstiff one, provided that the solutions are warped. A method to compute the all-pass chain coefficients and the optimum warping curves from sound samples is discussed. Once the optimum warping characteristic is found, the length of the dispersive delay line to be employed in the simulation is simply determined from the requirement of matching the desired fundamental frequency. The regularization of the dispersion curves by means of optimum unwarping is experimentally evaluated

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“…One method for realization of the warped IIR form requires the all-pass delay elements to be replaced with first order low pass sections. The filter structure will be stable if the warping is moderate and the filter order p is low [12]. Eq(5) can be expressed as a polynomial in z −1 /(1 − αz −1 ) to map the prediction coefficientsã k to a coefficient set used directly in a standard recursive filter structure.…”

Section: Filter Designmentioning

confidence: 99%

“…The lag free term must be incorporated into a delay structure which lags all terms equally to be realizable. Realizable warped recursive filter designs have been proposed to mediate this problem and elegant solutions exist [6][11] [12]. One method for realization of the warped IIR form requires the all-pass delay elements to be replaced with first order low pass sections.…”

Section: Filter Designmentioning

confidence: 99%

A Warped Bandwidth Expansion Filter

Boillot

Harris²

Proceedings. (ICASSP '05). IEEE International Conference on Acoustics, Speech, and Signal Processing, 2005.

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A warped filter is presented as a new speech enhancement method to adjust formant bandwidths on a critical band scale. The warped filter enhances perceived loudness without adding signal energy by exploiting the psychoacoustic nature of the auditory system. The critical band concept in auditory theory states that when the energy in a signal remains constant, loudness increases when the energy spreads beyond a critical bandwidth. A warped filter is proposed and developed to elevate the perceived loudness of clean speech by applying non-linear bandwidth expansion to the formant regions of vowels in accordance with the critical band scale. The filter has been inspired and motivated by the biological representation of loudness in the peripheral auditory system and the critical band concept of hearing. BACKGROUNDLoudness is intimately related to the critical band concept of hearing. The critical band concept states that spectral components separated by frequency so as to fall into different auditory channels are processed separately. The critical band concept states that when the energy in a signal remains constant, loudness will increase when a critical band is exceeded. This provides a compelling motivation for a means to increase speech loudness without adding energy to the signal via formant bandwidth expansion. This would be a practical consideration for power limited devices such as cell phones or hearing aids with high audio output requirements.Vowels are precipitated as candidates for formant bandwidth expansion since they are high energy, resonant, and spectrally smooth. Because vowels have formant bandwidths which increase with increasing frequency, the filter should elevate speech loudness by applying bandwidth expansion on a critical band scale. The LPC pole displacement Funding for this research was provided by the iDEN Technology Group and Product Development Group of Motorola technique is applied in the warped domain to increase formants on a critical band scale. The bandwidth adjustment technique has been used in spectral distortion measures [1], to sharpen formant bandwidths [2], as a postfilter [3], and recently to increase vowel loudness on a linear frequency scale [4]. The authors believe they are the first to apply the technique in the warped domain to adjust formants on a critical band scale to elevate perceived loudness [5]. The technique is used within the context of a Warped Linear Prediction Coefficient (WLPC) vocoder structure to provide the necessary degree of freedom for critical bandwidth adjustment [6]. In this paper we show how an off axis radius term is incorporated in the linear transformation of the warped coefficient set. POLE DISPLACEMENT MODELA technique used to alter formant bandwidth is shown in Eq (1) [7] and demonstrated in Fig(1). This provides a way to evaluate the Z transform on a circle with radius r greater than or less than the unit circle. For 0 < r < 1 the evaluation is on a circle closer to the poles and the contribution of the poles has effectively increased, thus sh...

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Realizable warped IIR filters and their properties

Cited by 17 publications

References 7 publications

Multichannel Dynamic-Range Compression Using Digital Frequency Warping

Multichannel Dynamic-Range Compression Using Digital Frequency Warping

Physically Inspired Models for the Synthesis of Stiff Strings with Dispersive Waveguides

A Warped Bandwidth Expansion Filter

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