JPH01160208A - Sound quality adjuster using group delay control - Google Patents

Abstract

PURPOSE:To obtain a group delaying coefficient corresponding to a group delaying frequency characteristic to be arbitrarily set by providing a group delaying coefficient arithmetic circuit to calculate the group delaying coefficient of an IIR type filter by means of group delay data from a group delaying frequency characteristic input circuit, and a group delaying coefficient control circuit to output the calculated group delaying coefficient to each IIR type filter. CONSTITUTION:A group delaying frequency characteristic input circuit 7, a group delaying coefficient arithmetic circuit 5 and a group delaying coefficient control circuit 4 are provided, and by making the group delaying coefficient obtained from the above- mentioned circuits into the coefficients of secondary IIR type filters 2-1-2-n to be connected in series, the secondary IIR type filters 2-1-2-n are made into APFs to change only the group delaying frequency characteristic. Thus, the arbitrary group delaying frequency characteristic can be set regardless of an amplitude frequency characteristic, and a sound quality can be variably changed. By using a digital memory 8 to store the reverse characteristic of the group delaying frequency characteristics of a loudspeaker and a magnetic tape recorder and using a manual/preset changeover switch 6, the sound quality can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a group delay control sound quality adjustment device that adjusts group delay frequency characteristics using an IIR type filter.

2. Description of the Related Art Conventionally, sound quality adjustment through group delay control of reproduced sound in audio reproduction has been considered important, but this adjustment has not been possible with conventional technology. In conventional methods, the amplitude frequency characteristics are changed using a graphic equalizer or tone control that utilizes the resonance of resistors, capacitors, etc., but the phase frequency characteristics also change accordingly.

This amplitude frequency characteristic greatly affects the tone.
However, it cannot be said that the sound quality will improve. On the other hand, in recent years, it has been discovered that sound quality is greatly affected by phase frequency characteristics (for example, ``Phase Distortion and Phase Equalization W/・In Audio Signal Processing''/7). '(Ph)
ase Distortion and PhaseE
Qualizatlon in Audio Sign
al ProcessingD, PREIS IAES
vol, 30411 1982 Nbvember))
, sound quality adjustment based on phase frequency characteristics is attracting attention. Hereinafter, a conventional graphic equalizer will be described with reference to the drawings.

FIG. 13 shows a conventional graphic equalizer. In FIG. 13, 21 is an input terminal, 22-1 to
22-n is an IIR type filter, 23 is an output terminal, 24 is an amplitude coefficient control circuit, 26 is an amplitude coefficient calculation circuit, and 26 is an amplitude frequency characteristic input circuit. The operation of the graphic equalizer configured as described above will be described below. First, an arbitrary amplitude frequency characteristic is set by the amplitude frequency characteristic input circuit 26. Next, it is input to the set amplitude coefficient calculation circuit 26, where it is input to the IIR type filters 22-1 to 22.
-Calculate the amplitude coefficient of n.

The calculated amplitude coefficients are sent by the amplitude coefficient control circuit 24 to each of the IIR filters 22-1 to 22-n. The signal from the input terminal 21 is input to the IIR type filters 22-1 to 22-n into which the amplitude coefficients have been inputted as described above to adjust the amplitude frequency characteristics and output from the output terminal 23.

Problems to be Solved by the Invention However, the above configuration has a problem in that although the amplitude frequency characteristic can be adjusted, only the group delay frequency characteristic cannot be adjusted.

The present invention solves the above problems and provides a group delay control sound quality adjustment device that can adjust only the group delay frequency characteristic without changing the amplitude frequency characteristic.

Means for Solving the Problems In order to achieve this object, the group delay control sound quality adjustment device of the present invention includes a signal processing section in which a plurality of n-th order IIR filters are connected in a row of fine stones, and an arbitrary group delay frequency characteristic. a group delay frequency characteristic input circuit that inputs the group delay frequency characteristic input circuit; a group delay coefficient calculation circuit that calculates the group delay coefficient of the IIR type filter using the group delay data from the group delay frequency characteristic input circuit; It consists of a group delay coefficient control circuit that outputs to the filter.

Function: With this configuration, arbitrary group delay frequency characteristics can be set.
Group delay coefficients corresponding to the characteristics are calculated and become coefficients for each IIR type filter. As the input signal passes through each IIR type filter, its group delay frequency characteristic is adjusted.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a group delay control sound quality adjustment device in an embodiment of the present invention. In Fig. 1, 1 is an input terminal, 2-1 to 2-n are secondary IIR type lines,
3 is an output terminal, 4 is a group delay coefficient control circuit, 6 is a group delay coefficient calculation circuit, 6 is a manual air) V/preset changeover switch, 7 is a group delay frequency characteristic input circuit, and 8 is a digital mesori.

It is now assumed that the manual/preset changeover switch 6 is configured to pass the signal from the group delay frequency characteristic input circuit 7 (manual mode). First, an arbitrary group delay frequency characteristic is set by the group delay frequency characteristic input circuit 7, and the group delay data is inputted to the group delay coefficient calculation circuit 5 to calculate each coefficient of the second-order IIR filters 2-1 to 2-n. calculate. The calculated group delay coefficient is calculated by the group delay coefficient control circuit 4.
The signal is sent to each second-order IIR filter 2-1 to 2-n. 2nd order IIR type filter 2- set as above
By passing the input signal from the input terminal 1 through the output terminals 1 to 2-n, a signal whose group delay frequency characteristic has been adjusted is output from the output terminal 3.

Next, the signal processing section (secondary IIR type filters 2-1 to 2-
A method of adjusting the group delay frequency characteristic in a series connection configuration of 1.0 to 3.0 mm is described below.

The transfer function of each second-order IIR type filter is given by the following equation.

This is illustrated in Figure 2. 'OI'1'a
2. The relationship between bl and B2 varies depending on the amplitude frequency characteristics to be realized. By the way, in order to adjust only the group delay frequency characteristic without changing the amplitude frequency characteristic, an all-pass filter (hereinafter abbreviated as APF) having a coefficient relationship such as the K, @) equation is defined.

This can be expressed in a diagram as shown in Figure 3. And this A
When PFs are connected in series, it is expressed as follows.

HA ('') = H'A = 1Hk (z) ・
...-"=(+) This is illustrated in Figure 4.

Here, in order for Hk(z) to be stable, its pole must be within the unit circle. This can be achieved by defining as follows.

+=-2ykcosθk in B1 ・・・・・・・・・・・・Sakaki) To B2 = 2 to γ (However, γ ≦1) From this, equation (3) becomes Here, β(,) is the phase frequency characteristic of the filter.

Next, the normalized group delay frequency characteristic τ(→ is defined as τ(→=shi≠!c7). The unnormalized group delay frequency characteristic τ*(ω*) is as follows. .

τ*(ω*)=τ(→TB ・・・・・・
・・・・・・・・・(8) However, T5=1/f3,
f3 is the sampling frequency. Also ω*=2π
f*tω=ω*/fs (f* is frequency).

From the above, the group delay frequency characteristic of the second-order APF as shown in FIG. 3 can be expressed as follows.

τ←)=τ1k(→+', k(-ω)...
(9) However, the group delay frequency characteristic of a filter in which secondary APFs are connected in series as shown in FIG. 4 is the sum of the individual characteristics.

However, 02N-=-〇k ・・・・・・・・・
...(12) τA(→=τA(-ω)=τA(ω+2π
)......(13). The above is
Simplified Design Op High-Order Recurrency Group-Delay Filters J (S
enhanced Des+1gnof High-
Order Recursive Group-Del
ayFi l term (P, A, BERNHA
RDT IEEE TRANSACTIONSON A
O:)USTIC3,5PEECH,AND5IGN
ALPROCESSING, VOL, ASSP
-28, As, αrOBER1980)).

The group delay coefficients of the second-order IIR filters 2-1 to 2-n can be determined using the above formula.

Figure 6 shows an APF realized with a certain second-order IIR type filter.
shows the group delay frequency characteristics of The amplitude frequency characteristic is constant, and the group delay frequency characteristic is expressed by equation (9), (10)
You can find the formula. In other words, the nine-group delay τ and the center frequency f(, can be set using equations (9) and (10).

Me, FIG. 7, and FIG. 8 are diagrams showing the setting of arbitrary group delay frequency characteristics using signal waveforms. First, in Fig. 6, in order to adjust the group delay frequency characteristic shown by the broken line,
This can be realized by making the group delay frequency characteristics of the next-order IIR filters 2-1 to 2-n as shown by the solid lines. In addition, in order to adjust the characteristics with a wide frequency band as shown by the broken line in FIG. 7 or the characteristics with large group delay as shown in the broken line in FIG. 1 to 2- The number of n may be increased.

Consider a case where a signal from the digital memory 8 is passed through the manual/preset changeover switch 6 (preset mode). This digital memory 8 stores in advance the group delay frequency characteristic of the speaker and the inverse characteristic of the group delay frequency characteristic of the magnetic tape recorder.

Let's take a speaker as an example. FIG. 9 shows the group delay frequency characteristics of a general speaker. Therefore, the inverse characteristic is stored in the digital memory 8.

This is the characteristic shown by the solid line in FIG.

This can be realized by making each of the second-order IIR filters 2-1 to 2-n have the characteristics shown by the broken lines.

As a result of the above, the sound reproduced from the speaker has its group delay frequency characteristics corrected, and the sound quality is improved accordingly.

As described above, according to this embodiment, the group delay frequency characteristic input circuit 71, the group delay coefficient calculation circuit 6. and a group delay coefficient control circuit 4, and the group delay coefficients obtained above are used as the coefficients of the series-connected second-order IIR filters 2-1 to 2-n, thereby creating the second-order IIR filter 2-1. ~2-
rs is an APF that changes only the group delay frequency characteristic. From this, the vibration characteristics can be set, and the sound quality can be varied in various ways. In addition, by using the digital memory 8 that stores the inverse characteristics of the group delay frequency characteristics of speakers and magnetic tape recorders, and the manual/preset selector switch 6, the group delay frequency characteristics that had an effect on the sound quality of speakers and magnetic tape recorders have been improved. can be corrected and the sound quality improved.

Other embodiments of the present invention will be described below with reference to the drawings.

FIG. 11 shows the configuration of a group delay control sound quality adjustment device in another embodiment of the present invention. In Figure 11,
9 is an input terminal, 1o-1 to 10-n are second-order IIR type filters, 11 is an output terminal, 12-1 to 12-n are group delay coefficient/amplitude coefficient changeover switches, 13 is a group delay coefficient control circuit, 14 16-1 to 16-2 are manual/preset changeover switches; 16 is a group delay frequency characteristic input circuit; 17 is a digital memory; 18 is a circuit;
20 is an amplitude coefficient calculation circuit.

The operation of the configuration of the group delay control sound quality adjustment device configured as described above will be explained below. This embodiment has a configuration that is a combination of the configuration shown in FIG. 1 and the configuration shown in FIG. 13. The order IIR type filters 1o-1 to 10-n can be used both for adjusting group delay frequency characteristics and for adjusting amplitude frequency characteristics. Since the group delay coefficient has already been explained in the previous embodiment, how to obtain the amplitude coefficient will be explained. (1
) can also be written as:

Now, the amplitude frequency characteristic to be realized is as shown in Fig. 12.
Assuming F characteristic, (12, β21r21a11β1゜γ
1 has the relationship shown by the following equation.

Here, F is the sampling frequency and Q is the sharpness of resonance.

fD is a set frequency.

Further, the gain G is expressed by the following equation.

lGl=201og (1+K) −・・・−・
By changing fD, Q, and K above (16), various amplitude frequency characteristics can be realized.

Then, the amplitude coefficient obtained by equation (16) is the second-order I
By sending the signal to the IR type filters 10-1 to 10-fi, the amplitude frequency characteristics of the input signal from the input terminal 9 can be adjusted.

As described above, according to this embodiment, the group delay coefficient obtained by the group delay frequency characteristic input circuit 1e, the group delay coefficient calculation circuit 14, and the group delay coefficient control circuit 13, the amplitude frequency characteristic input circuit 18, and the amplitude coefficient By selecting the amplitude coefficient obtained by the arithmetic circuit 20 and the amplitude coefficient control circuit 19 using the group delay coefficient/amplitude coefficient changeover switches 12-1 to 12-n, the group delay frequency characteristic and the amplitude frequency characteristic can be made independent. They can be adjusted simultaneously, or at the same time.

Note that in this embodiment, the signal processing section is implemented using a digital filter, but it may also be implemented using an analog filter.

Effects of the Invention By providing a group delay frequency characteristic input circuit, a group delay coefficient calculation circuit, and a group delay coefficient control circuit, the present invention can obtain a group delay coefficient according to an arbitrarily set group delay frequency characteristic. By using the coefficients of the IIR type filters connected in series, only the group delay frequency characteristic of the input signal can be adjusted. In addition, by storing the inverse characteristics of the group delay frequency characteristics of speakers and magnetic tape recorders in digital memory, it is possible to completely correct the group delay frequency characteristics of speakers and magnetic tape recorders and improve sound quality. This makes it possible to realize a group delay control sound quality adjustment device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a group delay control sound quality adjustment device in an embodiment of the present invention, FIG. 2 is a block diagram of a second-order IIR type filter, and FIG. 3 is a block diagram of a second-order IIR type APF. Figure 4 is a block diagram of secondary IIR type APFs connected in series, Figure 6 is a frequency characteristic diagram realized by secondary IIR type APFs, Figures 6, 7, 8, and 10 are 2 The following is a group delay frequency characteristic diagram realized by a configuration in which IIR type APFs are connected in series. Figure 9 is a group delay frequency characteristic diagram of a general subfield. Figure 11 is a group delay frequency characteristic diagram of another embodiment of the present invention. FIG. 12 is a block diagram of a control sound quality adjustment device, FIG. 12 is a MF% characteristic diagram using a second-order IIR type filter, and FIG. 13 is a block diagram of a conventional graphic equalizer. 1.9, 21... Input terminals, 2-1 to 2-n. 1o-1 to 10-n...Second-order IIR type filter, 3.11.23...Output terminal, 4,13...
...Group delay coefficient control circuit, 6, 14...Group delay coefficient calculation circuit, 6. 15-1.15-2...
・・Manual/preset selector switch, 7, 16・
...Group delay frequency characteristic input circuit, 8, 17...
...Digital memory, 12-1 to 12-n...
・Group delay coefficient/amplitude coefficient changeover switch, 18, 26・
...Amplitude frequency characteristic input circuit, 19.24...
...Amplitude coefficient control circuit, 20°26...Amplitude coefficient calculation circuit, 22-1 to 22-n...IIR
W filter. Name of agent: Patent attorney Toshio Nakao and 1 other person
2rlA aO Figure 3 Figure 5 c Zhou Yi Figure 6 Zhou Wan Maki Figure 7 For Qiu Figure 8 7!1 Langei Figure 9 Figure 1. Figure 7fl It
, & (1-IZJ” R bed CHL) Fig. 12

Claims (2)

[Claims] (1) A signal processing unit including a plurality of n-th order (n is a positive integer) IIR filters connected in series, a delay frequency characteristic input circuit that inputs an arbitrary group delay frequency characteristic, and the group delay frequency characteristic. a group delay coefficient calculation circuit that calculates a group delay coefficient of the IIR filter based on group delay data from an input circuit; and a group delay coefficient that outputs the group delay coefficient calculated by the group delay coefficient calculation circuit to each IIR filter. A group delay control sound quality adjustment device comprising: a control circuit. (2) The group delay control sound quality adjustment device according to claim 1, wherein the order of the IIR type filter is second order. (2) Claims characterized by comprising a digital memory storing the group delay frequency characteristics of a speaker or a magnetic tape recorder, and correcting the group delay frequency characteristics of the speaker or magnetic tape recorder using this digital memory. The group delay control sound quality adjustment device according to item 1.