GB2396538A - An apparatus and method for quantizing the phase of speech signal using perceptual weighting function - Google Patents
An apparatus and method for quantizing the phase of speech signal using perceptual weighting function Download PDFInfo
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- GB2396538A GB2396538A GB0406128A GB0406128A GB2396538A GB 2396538 A GB2396538 A GB 2396538A GB 0406128 A GB0406128 A GB 0406128A GB 0406128 A GB0406128 A GB 0406128A GB 2396538 A GB2396538 A GB 2396538A
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- phase
- weighting function
- speech signal
- perceptual weighting
- quantization
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
- G10L19/08—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
- G10L19/093—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters using sinusoidal excitation models
Abstract
The present invention provides an apparatus and a method for quantizing the phase of a speech signal using a perceptual weighting function. The apparatus for quantizing the phase of a speech signal using a perceptual weighting function includes a phase information extractor (100) for obtaining the phase of each harmonic frequency in a speech signal represented by the discrete sum of periodic signals having different harmonic frequency components, a quantization noise shaping unit (110) for controlling the amount of quantization noise of each phase using a perceptual weighting function, which makes quantization noise less than a predetermined just noticeable difference (JND) of the phase., a quantization bit assigner (120) for assigning quantization bits to each phase according to the controlled amount of quantization noise, and a scalar quantizer (130) for quantizing each phase by the assigned quantization bits. It is possible to improve the quality of encoded speech by quantizing phase information using a perceptual weighting function.
Description
GB 2396538 A continuation (74) Agent and/or Address for Service: Elkington
and Fife Prospect House, 8 Pembroke Road, SEVENOAKS, Kent, TN13 1XR, United Kingdom
N APPARATUS MIND METHOD FOR QUNTTIZLN-G PROSE OF SPEECH
SIGNAL USING PERCEPTUAL WEIGHTING FACTION
Field of the Invention
The present invention relates to quantization of the phase of a speech signal, and 5 more particularly, to an apparatus and a method for quantizing the phase of a speech signal using a perceptual weighting function.
Background to the Invention
It is essential to refer to the perceptual characteristics of the human auditory system with respect to the spectrum of a speech signal in speech encoding systems.
,. f.:-0 However, little attention has been paid to the perceptual characteristics of phase information. Recently, some interesting research addressing the importance of the perceptual characteristics of phase information in a speech signal has been conducted. It has been shown that humans' ability to distinguish different phase spectra is better than is often assumed.
15 In an apparatus for processing information on the phase of a speech signal disclosed in an application filed by the present applicant, a criterion was proposed to determine perceptually irrelevant phase information in a stationary section of a speech signal in the context of frequency domain representation of the speech signal. For harmonic signals, the criterion leads to the "critical phase frequency I, below which phase 20 information is irrelevant to the perceived quality of the signal. As mentioned above, the f (- speech signal phase information processing apparatus for distinguishing an important phase component was provided considering human auditory characteristics, so that the phase component of the speech signal is selectively coded or composed. However, there remain many problems to be solved in order to more effectively quantize the phase 25 information. One of them is how to effectively quantize the phase information above the critical phase frequency using the perceptual characteristics. In the present invention use of the perceptual characteristics of the human auditory system for quantizing the phase of the speech signal will be provided.
Summary' of The Invention
To solve the above problems, it is an object of the present invention to provide an apparatus for quantizing the phase of a speech signal, which is capable of improving the quality of encoded speech by quantizing phase information using a perceptual weighting 5 function, which makes phase quantization noise of, a speech signal less than a predetermined just noticeable difference (JND) of phase, and a method therefor Accordingly, to achieve the above object, according to an aspect of the present invention, there is provided an apparatus for quar.t'7ing the phase of a speech signal using a perceptual weighting function, comprising a phase information extractor for obtaining 10 the phase of each harmonic frequency in a speech signal represented by the discrete sum of periodic signals having^different harmonic frequency components, a quantization noise l: shaping unit for controlling the amount of quantization noise of each phase using a perceptual weighting function, which makes quantization noise less than a predetermined just noticeable difference (JND) of the phase, a quantization bit assigner for assigning 15 quantization bits to each phase according to the controlled amount of quantization noise, and a scalar quantizer for quantizing each phase by the assigned quantization bits According to another aspect of the present invention, there is provided another apparatus for quantizing the phase of a speech signal using a perceptual weighting function, comprising a phase information extractor for obtaining the phase of each 20 harmonic frequency in a speech signal represented by the discrete sum of periodic signals having different harmonic frequency components, a perceptual weighting function calculator for calculating a perceptual weighting function using a result obtained by -- measuring the JND of the phase at each harmonic frequency for a harmonic tone having else fundamental frequency of the speech signal, a comparator for comparing a previously 25 provided quantization estimation codebook with each phase by applying the perceptual weighting function, and a minimum value detector for detecting the munimum value among comparison values sequentially obtained from fine comparator and ourpuing fine Index of the quantization estimation code book corresponding to the minimum value To achieve the above object, according to an aspect of the present invention, there 30 Is provided a method for quantizing the phase of a speech signal using a perceptual A,eihting function, comprising the steps of (a) obtainin g the phase of each harmonic frequency in a speech signal represented by the discrete sum of periodic signals having different harmonic frequency components, (b) calculating a perceptual weighting function
using a result obtained bit the JIiD of the phase at each harmonic frequency for a harmonic tone having the fundamental frequency of the speech signal, (c) controlling the amount of quantization noise of each phase by calculating the amount of quantization noise from the perceptual weighnng function of each phase (d) assigning quantization bits 5 to each phase according to the controlled amount of quantization noise, and (e) quantizing each phase by the assigned quantization bits.
According to another aspect of the present invention, there is provided a method for quantizing the phase of a speech signal using a perceptual weighting function, comprising the steps of (a) obtaining the phase of each harmonic frequency in a speech 10 signal represented by the discrete sum of periodic signals having different harmonic fi:egllency components (h) calculating a perceptual weighting function using the result I obtained by measuring the JND of a phase at each harmonic frequency for a harmonic tone having the fundamental frequency of the speech signal, (c) comparing a previously provided quantization estimation code book with each phase by applying the perceptual 15 weighting function, and (d) detecting the minimum value among the comparison values sequentially obtained In the step (d) and outputting the index of the quantization estimation code book corresponding to the minimum value.
Brief Description of The Drawings
An example of the present Invention will now be described in detail with reference to the 20 accompanying drawings, in which: Figure 1 is a block diagram for describing a phase quantization apparatus i:: according to the present invention for scalar quantization; Figure 2 is a block diagram for describing a phase quantization apparatus according to the present invention for vector quantization; 25 Figure 3 is a flowchart for describing a phase quantization method according to the present invention: and Fugues 4A lo 4D show an experinental example of a Just noticeable difference (JUDD) of phase according to the present invention.
Detailed Description
30 FIG. 1 is a block diagram for describing a phase quantization apparatus according to the present invention for scalar quantization The phase quantization apparatus
includes a phase Defoliation extractor 100, a quantization noise shaping unit 110 a quanOzation bit assigner 120, and a scalar quantizer 130. The quantizaton noise shaping unit 110 includes a fundamental frequency setting unit 112. a perceptual weighting function calculator 114, and a weight assigner 116.
5 FIG. 3 is a flowchart for describing a phase quantization method according to the present invention. The operation of the apparatus shown m FIG. 1 will be described in detail with reference to FIG. 3.
The phase inflation exactor 100 obtains phase irolunatior1 frolic a speech signal to be quantized (step 300). A speech signal s(n) can be represented by Equation 1 10 in a harmonic speech encoding system, s (n) =AkcOs (k()On+8k) (1) k wherein, Ak, cue, and ok represent a spectral magnitude, a fundamental frequency, and a phase, at a kth harmonic frequency, respectively. That is, the speech signal s(n) is represented as the discrete sum of periodic signals having different harmonic frequency components. 15 The quantized phase Q(8k) Of the kth harmonic frequency Is represented by Equation 2, Wok) ok+...(2) i.;-. wherein, represents quantization noise. When it is assumed that a quantization noise source is stationary white noise with a uniform distribution over a quantization Interval and that the quantization noise is uncorrelated with an input, the variance of the 20 quantization noise Is represented by Equation 3, aE2= 1 ( A)...(3) wherein, represents the size of a quantization step. In the case where scalar guantization is performed with respect to the phase of each harmonic frequency, when it
Is assumed that the number of quantization bits assigned to represent each phase is B over the entire harmonic frequency, 2B = 21rlA. At this time, the total number of bits Blot for quantizing K phase components is represented by!!L as shown in Equation 4 B,ot=KB=K7og2(2;/) (4) In the present Invention, in order to make a quantized signal perceptually more 5 adjacent to an original signal, the above-mentioned uniform quantization noise is shaped with respect to each phase using a perceptual weighting function at each harmonic frequency. At this time, in the quantization apparatus and method according to the present motion, more bits are assigned to perceptually important phase comonnents; i- while keeping the total number of bits for all phase components the same as that in the 10 case where the quantization noise is uniform.
Referring to FIGS. 1 and 3, the quantization noise shaping unit llO controls the quantization step size of each phase using a perceptual weighting function, which makes the quantization noise less than a predetermined just noticeable difference (JND) of phase.
The JND obtained through a human-being oriented experiment represents the lowest level 15 of quantization noise at which a change in phase is detectable by human ears. That is, human-begs sense the change in phase when the quantization noise is equal to or more than the JND.
A way of controlling the magnitude of the quantization noise using the perceptual weighting function will now be described.
i : 20 According to Equation 3, the quantization noise is correlated with the quantization step, and the quantization step size varies according to each harmonic frequency. The quantization step size at the kth harmonic frequency is represented by Equation 5, ask V k...(5) wherein, ink represents a perceptual weighting function, and a smaller ok indicates that a phase Is perceptually more important. If the number of quantization bits for the 25 phase ink IS referred to as Bk, the total number of bits required to quantize K phase
components can be represented by Equation 5 by making the total number of bits for al] phase components equal to that of Equation 4 as mentioned above, K K B. to= Bk= logs (2r/^k) Og2(2r/)...6) k=1 k=] Putting Equation 5 into Equation 6 leads to Equation 7, V K _...(7!
if, ( Finally, the variance of quantization noise of the phase at the kth harmonic 5 frequency is represented by Equation 8, 2 1 Ask --(8) wherein, the quantization step size for the phase ilk iS represented by Equation 9, k ir... (9) It is noted from Equation 9 that the amount of quantization noise is controlled using the perceptual weighting function.
In the quantization noise shaping unit 110, the fundamental frequency setting unit l O 112 obtains a fundamental frequency from the speech signal represented by Equation 1.
The perceptual weighting function calculator 114 calculates the perceptual weighting function using the result obtained by measuring the just noiceabie difference (iND) of the phase at each harmonic frequency with respect to a harmonic tone havmg a fundamental frequency (step 310). The JND is a psychoacoustic term, which is used, in the present l 5 invention, for experiments on the human auditory sense with respect to changes in phase.
The JUDD of the phase was previously measured for a zero phase, flat spectrum periodic tone.
The weight assigner 116 controls the amount of quantization noise of each phase by caiculatmg the amount of quantization noise from the perceptual weighting function of each phase calculated by the perceptual weighting function calculator 114. That is, the weight assigner 116 assigns the quantization step size obtained by Equation 9 as a weight 5 t^ each phase obtained by the phase information extractor lOQ (step 320) The quantization bit assigner 120 assigns a quantization bit to each phase according to the amount of quantization noise controlled through the quantization noise controller 110 (step 330) That is, the quantization bit of each phase is obtained by putting the quantization step size obtained by Equation 9 into Equation 6. The scalar 10 quantizer 130 quantizes each phase by the assigned quantization bit.
An embodiment, in which the nercenhlal weighting function is calculated by the i perceptual weighting function calculator 114, will now be described.
In order to obtain an appropriate perceptual weighting function, psychoacoustic experiments were performed to measure the JND of a phase for a flat spectrum periodic 15 tone with the duration of 512 msec. The signal level was 52 dB/component throughout the experiments and the numbers of harmonics were set to be 39, 26, 19, and 11 for the fundamental frequencies of 100, 150, 200, and 350 Hz, respectively.
FIGS. 4A through 4D show the JNDs of the phases in the respective harmonic frequencies for the harmonic tones having the fundamental frequencies of 100, 150, 200, 20 and 350 Hz. The perceptual weighting function is superimposed on the plot as a solid line. In FIGS. 4A through 4D, a lower JND indicates that the modification of the phase at a corresponding harmonic frequency is quite perceptible to humans. It is noted by experiments that the JND of the phase is quite high at low frequencies, is minimal at a md-frequency range, and then increases again at high frequencies.
25 The perceptual weighting function is represented by Equation 10, as the function of a harmonic index k, 8,k.=ak 9+bk+c...(10) wherein. a, b, and c are estimated from the measured JND of the phase. Rather than constructing a polynomial suitable for the measured JND, the explicit utilization of some conditions, which was found to be useful for the generation of the weighting
function with respect to different fundamental frequencies, was adopted. First, the weighting function Irk iS defined for K<k<K, where K is the maximum harmonic index and K iS the index of a critical phase frequency, which is represented by Equation 11, tar (1- f) - 51...!11) o wherein, fit, Qear7 and BWm,n represent a fundamental frequency, an asymptotic 5 fiiRr quality at high frequencies, and the rnirirnuTn bandwidth for low frequency channels. This assumption is reasonable since the phase information below the critical phase frequency was shown to be irrelevant to the perceived quality. A1SO, the perceptual :eight'g function is assumed to take its max Plum i= 1) at -1 and K, based on the !--investigation of the JND measurements for different fundamental frequencies. In l O addition, the minimum of the perceptual weighting function is empirically determined by the ratio of the minimum JUDD to the maximum JND.
Table 1 shows listening test results according to the present invention. PQN denotes the percentage of the response showing that the quantization noise, to which the perceptual weighting function is applied, is selected to be equal to or closer to the original l 5 signal.
Table 1
Speaker, Vowel FO [Hz] 1 PQN (%) = 27rl3 = 2,r/5 i Male, lal 145. 5 78% 72% Male, Ill 127.0 85% 72% 20 Female, lal 205.1 54% 46% Female, lil 266.7 50% 50% From the results, we can see a clear preference for the perceptually weighted quantization noise m male speech. In addition, the smaller i\ means that more bits are assigned in phase information.
25 The quanization apparatus and method using the perceptual weighting function are described, taking scalar quantization as an example. However, the perceptual weighting function can be used m the distortion metric for vector quantization.
FIG. 2 is a block diagram for describing the phase qu=nhzaton apparatus according to the present invention for vector quantization. The phase quantization apparatus includes a phase information extractor 200, a fundamental frequency setting unit 210, a perceptual weighting function calculator 220, a comparator 230, a quantization estimation code book 240, and a mirimull1 value detector 250. Here description of the
members described with reference to FIG. 1 will be omitted.
The comparator 230 compares the previously provided quantization estimation code book 40 with, each phase by applying the perceptual weighting function of each phase, calculated by the perceptual weighting function calculator 220. For example, lO when phase information obtained by the speech signal is represented as 8=[3'82' ' Ilk]' and one of the phase information items stored in the quantization estimation code book 240 is represented as +', the comparator 230 obtains D( ,i') with respect to input phase information and all phase information items stored in the quantization estimation code book 240. At this time, D is represented as 15 D= (l -(k)[8k-k] by adding the perceptual weighting function. The minimum k value detector 250 detects the minimum value among the comparison values sequentially obtained by the comparator 230 and outputs the index of the quantization estimation code <- book 240 corresponding to the minimum value.
As mentioned above, the quality of the encoded speech is improved by quantizing 20 the phase information using the perceptual weighting function.
Claims (5)
1. An apparatus for quantizing the phase of a speech signal using a perceptual weighting function, comprising: 5 a phase information extractor for obtairn:ng the phase of each harmonic frequency in a speech signal represented by the discrete sum of periodic signals having different harmonic frequency components; a perceptual weighting function calculator for calculating a perceptual weighting function using a result obtained by measuring the JND of the phase at each 10 harmonicfrequency for a harmonic tone having the fundamental frequency of the speech signal a comparator for comparing a previously provided quantization estimation code book with each phase by applying the perceptual weighting function; and a minimum value detector for detecting the minimum value among 15 comparison values sequentially obtained from the comparator and outputting the index of the quantization estimation code book corresponding to the mir.imum value.
2. A method for quantizing the phase of a speech signal using a perceptual weighting function, comprising the steps of: , ...........
flu (a) oDrammg tne phase of each narmomc frequency In a speech signal represented by the discrete sum of periodic signals having different harmonic frequency components; (b) calculating a perceptual weighting function using the result obtained by measuring the JND of a phase at each harmonic frequency for a harmonic tone having 25 the fundamental frequency of the speech signal; (c) comparing a previously provided quantization estimation code book with each phase by applying the pcrccp+ u 1 -wcightirlg furlc+.ion; arid (d) detecting the minimum value among the comparison values sequentially obtained in the step (d) and outputting the index of the quantization 30 estimation code book corresponding to the minimum value.
3. The method of claim 2, wherein a perceptual weighting function as the function of a harmonic index k is represented by the following equation in the step 0, k = al + bk + c wherein, a, b, and c are estimated from the AND of the measured phase.
4. Am. apparatus for quantizing the phase of a speech signal using 2 persephA2l weighting function substantially as shown in and/or described with reference to Figure 10 2 of the accompanying drawings.
5. A method for quantizing the phase of a speech signal using a perceptual weighting function substantially as described with reference to Figure 2 of the . accompanying drawings.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020000026180A KR100363259B1 (en) | 2000-05-16 | 2000-05-16 | Apparatus and method for phase quantization of speech signal using perceptual weighting function |
| GB0024395A GB2362549B (en) | 2000-05-16 | 2000-10-05 | An apparatus and method for quantizing phase of speech signal using perceptual weighting function |
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| GB0406128D0 GB0406128D0 (en) | 2004-04-21 |
| GB2396538A true GB2396538A (en) | 2004-06-23 |
| GB2396538B GB2396538B (en) | 2004-11-03 |
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| GB0406128A Expired - Lifetime GB2396538B (en) | 2000-05-16 | 2000-10-05 | An apparatus and method for quantizing phase of speech signal using perceptual weighting function |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2122832A1 (en) * | 2007-03-14 | 2009-11-25 | Samsung Electronics Co., Ltd. | Method and apparatus for encoding/decoding audio signal containing noise at low bit rate |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5388181A (en) * | 1990-05-29 | 1995-02-07 | Anderson; David J. | Digital audio compression system |
| EP0910067A1 (en) * | 1996-07-01 | 1999-04-21 | Matsushita Electric Industrial Co., Ltd. | Audio signal coding and decoding methods and audio signal coder and decoder |
| JPH11184499A (en) * | 1997-12-24 | 1999-07-09 | Toshiba Corp | Voice encoding method and voice encoding method |
| US6292777B1 (en) * | 1998-02-06 | 2001-09-18 | Sony Corporation | Phase quantization method and apparatus |
| US6571207B1 (en) * | 1999-05-15 | 2003-05-27 | Samsung Electronics Co., Ltd. | Device for processing phase information of acoustic signal and method thereof |
-
2000
- 2000-10-05 GB GB0406128A patent/GB2396538B/en not_active Expired - Lifetime
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5388181A (en) * | 1990-05-29 | 1995-02-07 | Anderson; David J. | Digital audio compression system |
| EP0910067A1 (en) * | 1996-07-01 | 1999-04-21 | Matsushita Electric Industrial Co., Ltd. | Audio signal coding and decoding methods and audio signal coder and decoder |
| JPH11184499A (en) * | 1997-12-24 | 1999-07-09 | Toshiba Corp | Voice encoding method and voice encoding method |
| US6292777B1 (en) * | 1998-02-06 | 2001-09-18 | Sony Corporation | Phase quantization method and apparatus |
| US6571207B1 (en) * | 1999-05-15 | 2003-05-27 | Samsung Electronics Co., Ltd. | Device for processing phase information of acoustic signal and method thereof |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2122832A1 (en) * | 2007-03-14 | 2009-11-25 | Samsung Electronics Co., Ltd. | Method and apparatus for encoding/decoding audio signal containing noise at low bit rate |
| EP2122832A4 (en) * | 2007-03-14 | 2013-08-28 | Samsung Electronics Co Ltd | Method and apparatus for encoding/decoding audio signal containing noise at low bit rate |
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| Publication number | Publication date |
|---|---|
| GB2396538B (en) | 2004-11-03 |
| GB0406128D0 (en) | 2004-04-21 |
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