JP2705377B2 - Band division coding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a band division encoding method for compressing and encoding music signals and audio signals.

[0002]

2. Description of the Related Art In a conventional method of allocating the number of quantization bits for band division coding, the product of the downsampling frequency and the number of quantization bits to be allocated, that is, the information amount for each band becomes equal to the clarity index contribution of the band. (For example, Kazuo Nakata; "Efficient Coding of Speech", 1986, pp. 56-61).

[0003]

In the conventional method of allocating the number of quantization bits for band division coding, the number of quantization bits is allocated so that the information amount for each band becomes equal to the clarity index contribution. Has been effective in efficiently encoding. However, music and voice are recognized by human hearing. Due to the characteristics of human hearing, there is a case where human ears cannot be perceived even though there is information. Assigning the number of quantization bits to a signal in such a band
There is a problem that information important for human hearing cannot be efficiently encoded.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a band division coding method for allocating the number of quantization bits to a band having information important for human hearing.

[0005]

In order to solve the above-mentioned problems, the present invention comprises a first step of dividing an input signal into a plurality of frequency bands to obtain respective band-divided signals; A second step of allocating an appropriate number of quantization bits to, and a second step of quantizing each of the band division signals obtained in the first step with the number of quantization bits allocated in the second step. 3. The band division encoding method comprising: a step of calculating an index value based on the amplitude of the band division signal for each of the frequency bands;
The reference value set in advance for each frequency band is compared with the index value. If the index value is lower than the reference value, the number of quantization bits assigned to the frequency band is set to 0 bit.
And the step of performing

[0006]

When encoding is performed using the above-described band division encoding method, information important for human hearing can be encoded with high efficiency.

[0007]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining a quantization bit allocation method of band division coding according to the present invention. Reference numeral 1 denotes filter means for dividing an input signal into N bands. -It is composed of N N band division filters. Numeral 5 is a quantizing bit number allocating means, which detects an index value from a signal of each band divided into N bands by the filter means 1, a reference value previously set for each band, and the detecting means. And a comparing means for comparing the index values detected by the above method and setting the number of quantization bits to be assigned to the band to 0 when a preset condition is satisfied. Numeral 6 denotes a quantization means for quantizing each signal divided into N bands by the filter means 1 with the number of quantization bits assigned by the quantization bit number assignment means 5.

An embodiment of the quantization bit number assignment means 5 will be described with reference to a flowchart shown in FIG.

First, in step 1, the maximum value of the absolute value of the amplitude is detected as an index value of each band from a plurality of signals in each band. X ₁ is the maximum value of the first band, X ₂ is the maximum value of the second band, the X _N represents the maximum value of the N-th band. In step 2, i is set to 1, and in step 3, it is determined whether i is N or less. If i is equal to or smaller than N, the reference value TH (i) for the i-th band is read from (Table 1) in step 4.

[0010]

[Table 1]

In step 5, the maximum value X of the i-th band is
_i is compared with the reference value TH (i). If the conditional expression X _i ≤ TH (i) is satisfied, 0 bits are assigned to the i-th band in step 6. This reference value TH (i) represents the minimum audible level of the human ear for the i-th band, and signals below the reference value TH (i) are not perceived by the human ear, so that this conditional expression is satisfied. It is not appropriate to give the band the number of quantization bits. If the above conditional expression is not satisfied, in step 7, an appropriate number of quantization bits is assigned to the i-th band. In step 8, 1 is added to i, and the process returns to step 3. Steps 4 to 8 are repeated while the condition of step 3 is satisfied, and i is N
If it exceeds, it ends and moves to the next means. As described above, the number of quantization bits in all bands from 1 to N is determined. Here, step 1 corresponds to the detecting means, and steps 5 and 6 correspond to the comparing means.

In this embodiment, the maximum value of the absolute value of the amplitude of the signal in each band is used as the index value. (1) The maximum value of the square of the amplitude of the sampled signal in each band (2) Each band The desired band division coding can be performed by using the maximum value of the number of significant digits when the absolute value of the amplitude of the sampled signal is expressed as a power of two .

[0013]

The present invention provides a band division coding method as described above, which quantizes a signal in a band which is not important to human hearing with 0 bits.
A large number of quantization bits can be assigned to signals in a band necessary for human hearing, and encoding suitable for human hearing can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining an embodiment of a band division coding method according to the present invention;

FIG. 2 is a flowchart for explaining an embodiment of a quantization bit number allocating unit according to the present invention;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Filter means 2, 3, 4 Band division filter 5 Quantization bit number allocation means 6 Quantization means

Claims (5)

(57) [Claims] 1. A first step of dividing an input signal into a plurality of frequency bands to obtain respective band division signals, and a second step of allocating an appropriate number of quantization bits to each of the band division signals. And a third step of quantizing each of the band division signals obtained in the first step with the number of quantization bits allocated in the second step, and The second step is a step of calculating, for each of the frequency bands, an index value based on the amplitude of the band-divided signal; and a reference value and an index value set in advance for each of the frequency bands. And if the index value is smaller than the reference value, setting the number of quantization bits assigned to the frequency band to 0 bits . 2. The band division encoding method according to claim 1, wherein the reference value represents a minimum audible level perceived by a human ear in each frequency band. 3. A band division means for dividing an input signal into a plurality of frequency bands to obtain respective band division signals, and a quantization bit number allocation for allocating an appropriate quantization bit number to each of the band division signals. And a quantizing means for quantizing each band-divided signal obtained by said band dividing means with a quantization bit number allocated by said quantization bit number allocating means. The quantization bit number allocating means, for each of the frequency bands, when the index value based on the amplitude of the band division signal is less than a reference value set in advance for each frequency band, A band division encoding apparatus, wherein the number of quantization bits allocated to a frequency band is 0 bits . 4. The band division coding apparatus according to claim 3, wherein the reference value represents a minimum audible level perceived by a human ear in each frequency band. 5. A band division encoding method for dividing a signal into a plurality of bands, assigning an appropriate number of quantization bits to each band, and compressing and encoding the signals, wherein the method is not perceived by a human ear in each of the frequency bands. A signal which is lower than the minimum audible level is not coded.