Browsing by Author "Liu, Chi-Min"

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Autoregressive Modeling of Temporal/Spectral Envelopes With Finite-Length Discrete Trigonometric Transforms
(2010-07-01)
Hsu, Han-Wen
;
Liu, Chi-Min
;
資訊工程學系
;
Department of Computer Science
The theory of autoregressive (AR) modeling, also known as linear prediction, has been established by the Fourier analysis of infinite discrete-time sequences or continuous-time signals. Nevertheless, for various finite-length discrete trigonometric transforms (DTTs), including the discrete cosine and sine transforms of different types, the theory is not well established. Several DTTs have been used in current audio coding, and the AR modeling method can be applied to reduce coding artifacts or exploit data redundancies. This paper systematically develops the AR modeling fundamentals of temporal and spectral envelopes for the sixteen members of the DTTs. This paper first considers the AR modeling in the generalized discrete Fourier transforms (GDFTs). Then, we derive the modeling to all the DTTs by introducing the analytic transforms which convert the real-valued vectors into complex-valued ones. Through the process, we build the compact matrix representations for the AR modeling of the DTTs in both time domain and DTT domain. These compact forms also illustrate that the AR modeling for the envelopes can be performed through the Hilbert envelope and the power envelope. These compact forms can be used to develop new coding technologies or examine the possible defects in the existing AR modeling methods for DTTs, We apply the forms to analyze the current temporal noise shaping (TNS) tool in MPEG-2/4 advanced audio coding (AAC).
Decimation-Whitening Filter in Spectral Band Replication
(2011-11-01)
Hsu, Han-Wen
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Liu, Chi-Min
;
資訊工程學系
;
Department of Computer Science
MPEG-4 High-Efficiency Advanced Audio Coding (HE-AAC) has adopted spectral band replication (SBR) to efficiently compress the high-frequency part of the audio. In SBR, linear prediction is applied to low-frequency subbands to suppress tonal components and smooth the associated spectra for replicating to high-frequency bands. Such a tone-suppressing process is referred to as whitening filtering. In SBR, to avoid the alias artifact incurred by spectral adjustment, a complex filterbank instead of real filterbank is adopted. For QMF subbands, this paper demonstrates that the linear prediction defined in the SBR standard results in a predictive bias. A new whitening filter, called the decimation-whitening filter, is proposed to eliminate the predictive bias and provide advantages in terms of noise-to-signal ratio measure, frequency resolution, energy leakage, and computational complexity for SBR.
Efficient method and apparatus for convolution of input signals
(2005-10-06)
Liu, Chi-Min
;
Lee, Win-Chieh
;
Yang, Chung-Han
An FIR-based apparatus performs fast convolution in the frequency domain for generating room reverberation. The impulse response of a room is segmented and transformed by FFT to form a plurality of segmented room frequency spectra. The input signal to the room is also segmented and transformed to form segmented input frequency spectra. Either overlap-and-add method or overlap-and-save method is applied in the apparatus to accomplish the fast convolution based on the multiplication of segmented input frequency spectrum and segmented room frequency spectrum. To further reduce the complexity of the convolution, a segmented room frequency spectrum is processed to remove high frequency components before being used in the fast convolution according to a perceptual criterion.
Fast motion estimation using N-queen pixel decimation
(2003-07-03)
Chiang, Tihao
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Liu, Chi-Min
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Wang, Chung-Neng
;
Yang, Shin-Wei
The present invention proposes a fast motion estimation using N-queen pixel decimation, whereby after a reference block and a block to be processed are selected in a video sequence, an N×N queens pattern is used for pixel decimation to perform block match, thereby obtaining a good enough block difference value. The present invention combines pixel decimation with fast motion estimation for search points reduction to achieve the object of simplifying computational complexity of motion estimation. Therefore, the present invention can sieve out sufficiently representative pixels and will not increase extra computational complexity.
Fast Radix-q and Mixed-Radix Algorithms for Type-IV DCT
(2008)
Hsu, Han-Wen
;
Liu, Chi-Min
;
資訊工程學系
;
Department of Computer Science
This letter proposes a fast radix-q algorithm to compute type-IV discrete cosine transform (DCT) of the length q(lambda), where q is an odd positive integer. The proposed fast radix-q algorithm has merits in computational complexity, parallelism, and numerical stability over existing algorithms. Furthermore, the fast radix-q algorithm is used to develop the fast mixed-radix type-II/type-IV DCT algorithm for composite lengths.