DE112008003153T5 - Frequency band determination method for shaping quantization noise and method of forming transient noise using this method - Google Patents

Abstract

A frequency band determination method for shaping quantization noise, comprising:
Checking whether audio signals obtained from low-pass filtering are transient;
Determining a predetermined frequency band to apply as a frequency band to be used for shaping quantization noise when the audio signals are not transient; and
Determining an extended frequency band extended beyond the predetermined frequency band to apply as a frequency band to be applied when the audio signals are transient.

Description

Technical area

The The present invention relates to a frequency band determination method for shaping quantization noise and for this method using method for shaping transient noise. Especially The method shapes the noise using a long block and reduces a pre-echo and musical noise by calculating, whether an applied frequency band is a general frequency band and An extended frequency band is based on the fact whether audio signals are transient signals.

This work was supported by the IT R & D program for MIC / IITA [ 2007-S-005-01, "Development of Rich Media Broadcasting Technologies through Advanced Audio and Video Codec Technologies" ].

Technical background

In a highly efficient advanced audio coding technology (High Efficiency Advanced Audio Coding, HE-AAC) becomes an algorithm for shaping temporal noise shaping (TNS), the one of algorithms for shaping quantization noise, used to effectively represent transient signals. Therefore reduced the TNS algorithm is a pre-echo.

In spite of however, the use of the TNS algorithm occurs at low bit rates often the pre-echo and the musical noise.

Around sound quality in HE-ACC audio coding technology with perceptibly transparent coding, that should be Quantization noise does not exceed a masking threshold. In a perceptual coding technology, a frequency signal analysis method however, the quantization noise is coded and then spread wide in the time domain. That's why it's at low bit rates difficult to fulfill the condition that the quantization noise does not exceed the masking threshold in the time domain.

For example is in AAC audio coding technology, which is generally 1024 modified discrete cosine transformation coefficients (Modified Discrete Cosine Transform, MDCT) uses quantization noise distributed with a 48-kzz sampling rate over 40 ms. These Distribution can cause audible artifacts when the Signals are transient signals. At this time, the quantization noise may be noticeable are detected before the transient signals are generated. This quantization noise is called the pre-echo phenomenon.

In the TNS algorithm that has been developed to deal with the pre-echo phenomenon To deal effectively, the form of quantization noise, the is spread wide in the time domain, set to a masking effect to have.

Of the TNS algorithm uses a linear predictive coding (Linear Predictive Coding, LPC), based on a duality between the time domain and a frequency domain. table 1 explains an optimal coding method for Sound signals and transient signals regarding the duality.

Table 1

The means that in the frequency domain the optional coding method for the sound signals with a certain frequency a direct one Coding method is a frequency coefficient coding used. In the time domain is the optimal coding method for the sound signals with a certain frequency are a predictive one Coding method using LPC coding.

If whereas duality is considered, is in the frequency domain the optimal coding method for the transient signals the predictive coding method that uses the frequency coefficient prediction coding used. In the time domain is the optional coding method for the transient signals the direct coding method, that uses the time-sample encoding.

Of the TNS algorithm is based on the predictive coding method applied in the frequency domain.

Table 2 shows the frequency band that TNS applies. Table 2 Types of blocks long block short block Frequency band applying TNS 1275 Hz ~ 2750 H ~

in this connection is the TNS frequency range (band) corresponding to the block length classified into a long block and a short block. The Frequency band applying the TNS algorithm is more than 1275 Hz for the long block and more than 2750 Hz for the short block.

The means that in the long block the TNS algorithm is set to one Frequency range from a frequency band of 1800 Hz up to a Cut-off frequency at which spectral band replication (Spectrum Band Replication, SBR) starts being applied. On the other hand, in the short block the TNS algorithm on a frequency range of one frequency band from 2750 Hz to the cutoff frequency at which the SBR starts. Occurs in a band below the above frequency bands the pre-echo frequently.

Around to further reduce the pre-echo, a block switch is executed. Block switching refers to the process of replacing a long one Window with a frame length through a short window with 1/8 of the frame length. The block switching between the long block and the short block is used to do the pre-echo Apply the quantization noise effect only in the short block perceptibly improve.

However, if the signals are stable and the bitrate is low, the short window may strike one against cause some effect. Since the bit in the low bit rate is insufficient, frequency components lost in each short block are shown as spectral holes. The spectral holes are intermittently connected on a time axis in a corresponding frame to cause the musical noise. That is, at the low bit rate with insufficient bit, when the long block is used instead of the short block, the pre-echo occurs. In addition, at low bit rate with insufficient bit, when the short block is excessively used, the musical noise occurs.

Disclosure of the invention

Technical problem

A Embodiment of the present invention is directed to a frequency band determination method for shaping quantization noise and a method of forming transient that uses this method To create noise.

In the conventional technology for shaping temporal Noise (Temporal Noise Shaping, TNS) can be used when the bit rate low, a pre-echo and musical noise in transient Blocks can not be prevented. An object of the present Invention is to solve the above problems.

Consequently This invention provides a method for determining a frequency range for shaping quantization noise using a long one Blocks in accordance with an applied frequency band, the as a general frequency band or as an extension frequency band classified, and depending on whether audio signals transient signals are to the pre-echo and the musical noise to effectively reduce, and a method using this method for shaping transient noise.

The Objects of the present invention are not related to those mentioned above Tasks restricted. Other tasks and benefits of The present invention can be understood by the following description be understood and will be with reference to the embodiments of the present invention. It is also for those skilled in the art will appreciate that Objects and advantages of the present invention by the means which are claimed and realized by combinations thereof can be.

Technical solution

According to one Aspect of the present invention is a frequency band determination method for shaping quantization noise, comprising: checking, whether audio signals obtained from low-pass filtering are transient signals, determining a given frequency band, to apply it as a frequency band due to the shaping of quantization noise is to be used when the audio signals are not transient, and Determine an extended frequency band that exceeds the specified one Frequency band is extended to apply it as a frequency band, to apply when the audio signals are transient.

Advantageous effects

These Invention forms quantization noise of audio signals using a long block in accordance with a frequency band for the application of an algorithm for shaping temporal Noise (TNS algorithm) and classifies the frequency band in a general frequency band and an extension frequency band in accordance with whether the audio signals transient Signals are. Thus, a pre-echo and musical Noise can be easily reduced.

Therefore In this invention, the sound quality is better than with a method of shaping quantization noise that is conventional TNS algorithm used. The method of the present invention using the long block reduces the pre-echo more effectively as the typical procedure. Furthermore, it is possible to almost to create the same performance in the process that only the short block can be obtained.

Therefore In this invention, the short block does not become excessive used, whereby the musical noise can be reduced.

Brief description of the drawings

1 Fig. 10 is a block diagram showing an apparatus for processing the shaping of temporal noise (TNS processing) according to an embodiment of the present invention.

2 and 3 show the pre-echo according to the transient index.

4 FIG. 10 is a flowchart describing a method of shaping quantization noise in a low frequency band using a long block according to an embodiment of the present invention. FIG.

Best way to run the invention

The Advantages, features and aspects of the invention will become apparent from the following Description of the embodiments, which are attached to the attached Drawings reference is made and shown below, clearly. Therefore, those skilled in the art can the technological concept and the scope of the invention simple To run. If it is further assumed that an accurate Description of a related art a point of the present Could obscure the invention, the detailed description not given here. The preferred embodiments of The present invention will hereinafter be described in detail with reference to FIG described on the accompanying drawings.

1 Fig. 10 is a block diagram showing an apparatus for processing the shaping of a temporal noise (TNS processing) according to an embodiment of the present invention.

In 1 contains a TNS processing device 100 a TNS determination device 110 and a TNS encoder 120 ,

The TNS processing device 100 reshapes the quantization noise in a time domain in a filter bank window to make the noise imperceptible. Hereinafter, the TNS processing device 100 in a general HE-ACC encoding device.

The TNS determining device 110 determines whether a TNS process is applied or not.

wobei k und n eine MDCT-Koeffizienteneinheit bzw. eine Skalenfaktoreinheit darstellen.More specifically, the TNS determiner multiplies 110 a weight as in Eq. 1 to calculate a linear predictive coding (LPC) of a pre-computed modified discrete cosine transform (MDCT) spectrum. X w (k) = X (k) · wfac (k) (equation 1) in which

where k and n represent an MDCT coefficient unit and a scale factor unit, respectively.

This means that Eq. 1 normalized to the energy of a corresponding scale band. The MDCT spectrum range is applied to a given range. Therefore, the TNS determining means determines 110 a frequency range (band) for the application of the LPC.

wobei k und n eine MDCT-Koeffizienteneinheit bzw. eine Skalenfaktoreinheit darstellen.The TNS determination unit 110 applies a smoothing filter to the normalized spectrum. This is for the LPC analysis. The smoothing filtering means down-filtering in a frequency band range from an LPC interrupt frequency to an LPC operating frequency by the one shown in Eq. 2 shown process.

where k and n represent an MDCT coefficient unit and a scale factor unit, respectively.

wobei k und n eine MDCT-Koeffizienteneinheit bzw. eine Skalenfaktoreinheit repräsentieren.On the other hand, the TNS determining means performs 110 up-filtering in a frequency band range from the LPC operating frequency to a cut-off frequency. Eq. 3 shows the up-filtering process.

where k and n represent an MDCT coefficient unit and a scale factor unit, respectively.

The TNS determining device 110 calculates an autocorrelation function and the LPC using a Levinson-Durbin algorithm. The TNS determining device 110 detects a Partial Autocorrelation Coefficient (PARCOR) and calculates a prediction gain based on the result of the calculation using the Levinson-Durbin algorithm.

If the calculated prediction gain exceeds a threshold, the TNS determiner determines 110 that the LPC should be performed on the spectrum and that a TNS algorithm should be applied to the current window.

The TNS encoder 120 performs a quantization simulation in an order of high to low PARCOR coefficients to determine the TNS order and a first coefficient not less than the threshold, e.g. B. 0.1, is. This is to use only effective TNS PARCOR coefficients.

The TNS encoder 120 passes through an LPC filter of the particular order and coefficient and applies the TNS algorithm to the MDCT spectral coefficients to perform the encoding. The ACC coding is performed using the applied MDCT spectral coefficient.

These Invention extends the TNS algorithm down to low Frequencies such as 100 Hz and applies it to it. Since here the TNS algorithm is applied extended, the pre-echo is reduced. The sound components of the frequency that use the TNS algorithm, d. H. the low frequencies, however, can be distorted become.

Therefore At the same time, this invention uses the general TNS algorithm and the extension TNS algorithm. That means that this invention determines if they use the general TNS algorithm or the extension TNS algorithm then applies the TNS algorithm based on the Determination result. A reference for the provision is the extension of the extended low Frequency.

in the The following are conditions for determining whether the TNS algorithm or the extension TNS algorithm applied is described.

First, the TNS determiner determines 110 whether the general TNS algorithm is on can be used or not. If the block switch result is transient only in the low frequency band, the TNS determiner applies 110 the extension TNS algorithm.

Second, the TNS determiner applies 110 the extension TNS algorithm when the prediction gain in the frequency band applying the TNS algorithm extended up to 100 Hz exceeds the threshold and the transient signals with increased energy are between the fourth and seventh frames of eight frames. On the other hand, the TNS determining means applies 110 the general TNS algorithm when the transient signals with reduced energy are between the zeroth and the third frame of eight frames.

Of the Transient index of the transient signals 0 to 7 gives the transient index by the block switching between the short block and the long block is determined. Each block gives the individual points at which the corresponding frame is divided into eight frames becomes. This transient index is used for effective coding used for the HE-ACC and reference is made to it, when eight short blocks tied together into four groups to apply the short blocks. The reference value for The TNS algorithm is the transient index of the signals passing through the low frequency will be sent and filtered.

Under The second condition described above becomes the effect of the pre-echo and affects the extent of the impact the extension TNS application. Here is the time for the pre-echo equal to the corresponding window length.

The means that when the transient section with increased Energy is located in a front section of the corresponding frame, the pre-echo occurs in a narrower area. If, on the other hand the transient section with increased energy in one End portion of the corresponding frame is located, the pre-echo occurs in a wider area.

The 2 and 3 show the pre-echo according to the transient index.

In 2 gives a first transient index 101 a transient signal in an end portion of the frame. Because here is the first pre-echo 102 located in the end portion of the frame, the first pre-echo occurs 102 in a larger area.

In 3 gives a second transient index 103 a transient signal in a front portion of the frame. If here is the second transient index 103 located in the end portion of the frame has the second pre-echo 104 a greater impact than the first pre-echo 102 , this in 2 is shown. Therefore, the TNS determining means determines 110 that the extension DNS algorithm is applied.

4 Fig. 10 is a flowchart describing a method of shaping the quantization noise in a low frequency band using a long block according to an embodiment of the present invention.

A TNS determination device 110 calculates a prediction gain of audio signals using a long block in step S302. That is, the TNS determiner 110 calculates the autocorrelation function and the LPC using a Levinson-Durbin algorithm and obtains a PARCOR from the computation result and calculates a prediction gain.

The TNS determining device 110 determines in step S304 whether the calculated prediction gain exceeds the threshold.

wobei H(z) die Tiefpassfilterfunktion angibt. Auf H(z) können verschiedene Tiefpassfilterfunktionen angewendet werden. In der Tiefpassfilterungsfähigkeit der verschiedenen Tiefpassfilterfunktionen besteht kein großer Unterschied. Die TNS-Bestimmungseinrichtung 110 verwendet das Tiefpassfilter, um das Signal in einem niedrigen Frequenzband unter 1 kHz zu erfassen.The TNS determining device 110 Separately, perform low pass filtering using the low pass filter to determine frequency components in an extension band. This is to use only the long block. An example of the low pass filter function is given in Eq. 4.

where H (z) indicates the low pass filter function. On H (z) various low pass filter functions can be applied. There is not much difference in the low pass filtering capability of the various low pass filter functions. The TNS determining device 110 uses the low-pass filter to get the signal in a low frequency band below 1 kHz.

Based on the comparison result in step S304, the TNS determining means checks 110 if the prediction gain exceeds the threshold, in step S306, whether the low-pass filtered and filtered signals are transient. That is, the TNS determiner 110 determines, in accordance with the result of the check in step S306, the frequency band used for shaping the quantization noise. On the other hand, if the prediction gain does not exceed the threshold, the TNS determiner calculates 110 in step S314, the prediction gain of the expansion band and checks whether the prediction gain of the expansion band exceeds the threshold. Here, it is checked whether the signals sent and filtered by the low frequency pass are transient by using the block switching algorithm in the AAC device.

Based on the result of the check in step S306, the TNS determining means performs 110 when the signals sent and filtered by the low frequency are transient, no resetting of a masking threshold 308 out. On the other hand, if the signals sent and filtered by the low frequency are not transient, the TNS determiner determines 110 in that the general TNS algorithm is applied, in step 312.

If the masking threshold is not reset, is displayed in general TNS algorithm the threshold in the frequency band, which does not apply the TNS algorithm, lowered the bit effectively to use. On the other hand, in this invention, the extension TNS algorithm used, since here all frequency bands the TNS algorithm do not re-set the masking threshold required.

The TNS determining device 110 does not reset the masking threshold and in step S310 expands the frequency band using the TNS algorithm down to the frequency of about 100 Hz. The TNS Encoder 120 recalculates the coefficient based on the TNS algorithm which is extended to the low frequency band, whereupon it performs the TNS coding.

Based on the check result in step S314, the TNS determining means analyzes 110 when the prediction gain of the extension band exceeds the threshold, the type and index of the transient signal sent and filtered by the low frequency, and checks in step S316 if the effect of the pre-echo exceeds a reference value. That is, the TNS determiner 110 determines whether or not the quantization noise is formed based on the analysis result in step 316. For example, the TNS determining means determines 110 in that the effect of the pre-echo exceeds the reference value, and applies the TNS algorithm if the type and index of the transient with increased energy are in the end portion of the corresponding frame, or if the type and index of the low-energy transient in the front section of the corresponding frame.

On the other hand, if in step S314 the prediction gain of the extension band based on the test result does not exceed the threshold, the TNS determiner applies 110 the TNS is not on in step S318.

The TNS determining device 110 does not reset the masking threshold in step S308 if, based on the result of the check in step S316, the effect of the pre-echo is large. On the other hand, if the effect of the pre-echo is small, the TNS determiner applies 110 do not start the TNS algorithm in step S318.

As has been described above, the technology of the present Invention can be realized as a program. From a computer programmer of the related area can easily access a code and a code segment, that make up the program. Besides that is the realized program in a computer readable recording medium, d. H. stored in an information storage medium and is used by the computer read and executed, eliminating the process of the present invention. The recording medium includes all types of recording media used by the computer can be read.

The present application contains the subject of the invention Korean Patent Application Nos. 2007-0119413 and 2008-0048837 , filed with the Korean Patent Office on 21 November 2007 or on May 26, 2008, the entire contents of which are incorporated herein by reference.

Even though the present invention with reference to certain preferred embodiments has been described to those skilled in the art clearly that made various changes and modifications can be without departing from the scope of the invention, such as it is defined in the following claims.

Summary

One Frequency band determination method for shaping quantization noise includes checking for audio signals coming from low-pass filtering are transient, determining a given Frequency band to apply it as a frequency band used for the shaping of quantization noise is to be applied when the audio signals are not transient, and determining an extended frequency band, that extends beyond the given frequency band is to apply it as a frequency band to be applied if the audio signals are transient.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - KR 2007-0119413 [0064]
• - KR 2008-0048837 [0064]

Cited non-patent literature

• - 2007-S-005-01, "Development of Richmedia Broadcasting Technologies through Advanced Audio and Video Codec Technologies" [0002]

Claims (10)

Frequency band determination method for shaping quantization noise, comprising: Check if Audio signals obtained from low-pass filtering, transient are; Determine a given frequency band to use as to apply a frequency band that is used to form quantization noise apply when the audio signals are not transient; and Determine an extended frequency band that exceeds the given Frequency band is extended to apply it as a frequency band, to apply when the audio signals are transient. The method of claim 1, wherein the predetermined Frequency band to be applied, a particular TNS frequency band which is applied to a general TNS algorithm. The method of claim 2, wherein the extended frequency band is extended down to a frequency band lower than a particular TNS frequency band. Method for shaping quantization noise, the method comprising: Comparing a prediction gain of audio signals calculated using a long block be, with a threshold; Determining a frequency which is to be used for shaping quantization noise Check whether the audio signals obtained by low-pass filtering are transient when the prediction gain exceeds the threshold; and Apply the shaping of quantization noise to the Audio signals according to the predetermined frequency band. The method of claim 4, wherein determining a The frequency to be applied further comprises: Check if transiently obtains the audio signals obtained from the low-pass filtering are; Determining a predetermined frequency band as the frequency band, to apply to the shaping of quantization noise when the Audio signals are not transient; and Determine an extended one Frequency band beyond the specified frequency band is extended to apply it as a frequency band to apply is when the audio signals are transient. The method of claim 5, further comprising: Determine, whether the shaping of quantization noise is performed should be checked by checking whether a prediction gain the extended frequency band exceeds a threshold, if the prediction gain does not exceed the threshold. Method according to claim 6, wherein the fact of whether the shaping of quantization noise is performed should, by checking the type of transient and the transient index the audio signals is determined when the prediction gain the extended amplification of the extended frequency band exceeds the threshold. The method of claim 7, wherein determining the Forming quantization noise is executed when the transient type and the transient index of the audio signals have increased energy and become in one end section of a corresponding frame. The method of claim 7, wherein determining the Forming quantization noise is executed when the transient type and the transient index of the audio signals have reduced energy and get in the front section of a corresponding Frame. The method of claim 7, wherein the molding of Quantization noise in the extended frequency band a masking threshold does not reset.