JPS625713A - Sound quality compensating circuit for narrow band transmission system - Google Patents

Abstract

PURPOSE:To improve the sound quality of a narrow band sound signal transmission system by providing a compensation means whose delay time is changed in response to the audible frequency. CONSTITUTION:The input signal is divided into N frequency bands by a dividing filter. In such a case, a linear axis or a logarithmic axis is used the frequency axis, and the latter requires a fewer N. Delay times tau1, tau2...tauN of a delay circuit 8 have a distribution compensating the frequency versus delay time characteristic of the audible system. In using a tapped delay line, the delay time is adjusted while listening to a reproduced sound by audible sense so as to the optimum overall characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The invention relates to a sound quality compensation circuit used in an acoustic signal transmission system.

B. By adding a compensation circuit having characteristics opposite to the time-delay time characteristics of the auditory sense to the acoustic signal transmission system, the transmission band can be narrowed (even if the transmission band is narrow) in the case of a sound source with many pre-transients. The auditory sense perceives sounds with a good rise, and can provide a powerful sound to those who hear it. Specifically, the above compensation circuit inserts the transmission band on the complement side, and reduces the delay time to zero for low frequency components. Alternatively, a single or multiple stages of active all-pass circuits may be connected in series to reduce the delay time at high frequencies.

C Conventional technology Conventionally, in acoustic signal transmission systems, phase characteristics (vs. frequency)
Almost no compensation was provided.

The basis for this is that the human sense of hearing is hardly sensitive to phase. For example, the synthesis of the fundamental wave and its third harmonic is as shown in Figure 4. In Figures 4 (a) and (b), the phases of the fundamental wave and the third harmonic are different, but there is an audible difference. It is known that /h is small.

However, in recent years, physiological and psychological research on hearing has progressed, and it has become possible to measure the temporal frequency versus delay time characteristics.

Figure 5 (al is the target of the physiological experiment on cat hearing (d)
e Boer 2 5ynthetic
whole-nerve actionpoLent
+als J+Acoust, Soc, Am-*
Vol 58゜A5. CP, P, 1034) Nov, 1
975) and the same figure (bJ is an example measured by the inventor, and in both cases, the delay is smaller at high frequencies than at low frequencies.

This means that a signal with the waveform of (a) in FIG. 4 is perceived as a signal with the waveform of (b).

In a wideband acoustic signal system, the phase characteristics of J1!11jt described above need not be taken into consideration much. For example, it is common that the size of the frequency component hardly changes and the low-frequency components are heard with a delay in the case where the frequency component is directly transmitted to the original f' and when the frequency component is transmitted directly to the frequency component of the wideband signal system. There is no requirement to change the phase characteristics.

However, in a narrowband transmission system, the high frequency components of the signal are naturally deleted or attenuated, making it far from faithfully reproducing the original sound. This is why TLAM radio sounds less crisp than FM. That is, the conventional narrowband transmission system has the disadvantage that when the signal is transmitted through the auditory sense, the rise of the waveform becomes worse at 9 as shown in FIG. 3(b).

D Problems to be Solved by the Invention An object of the present invention is to provide a compensation circuit that can improve the sound of a narrowband acoustic signal transmission system by 3 feet.

E Means for Solving the Problems In order to achieve the above objective Y, the f-quality compensation circuit for the narrowband transmission system according to the present invention is provided in an acoustic signal transmission system that provides an acoustic signal to the auditory senses through a speaker, The key point is to include compensation means for changing the delay time depending on the frequency of the range. The above compensation means.

A filter that divides a signal into a plurality of different frequency bands, a delay machine that is provided corresponding to the plurality of outputs of the filter and has a delay time corresponding to the respective frequency R, and a delay machine that adds the outputs of these delays. or consisting of a single or a plurality of cascaded active all-pass circuits.

F Effect Figure 6 shows the original sound of a 50 Hz square wave (aJ), the waveform (bJ) after passing through a narrowband transmission system and the auditory sense (bJ), and (c) where a compensation circuit is provided in the state of bJ. For convenience of calculation, it was assumed that up to the 9th high frequency band passes through. (The compensation circuit of CL was made to have the inverse characteristic of auditory frequency-delay time shown in m4 diagram (b).

As is clear from comparing Figure 6 (cJ and (bl), (
In C), the rise of the 'CtfL shape is better than that of bJ.In other words, the rise of the CtfL shape is better in response to more or less shocking sounds.In other words, the rise of the Nya shape is better than 9. d
If expressed as e/dt, the present invention can also be applied to the R wave number-delay time characteristic in the case of a narrowband transmission system (acoustic equipment). A signal t that compensates and has a good rise for hearing.
Provides improved sound quality 'fly! ' It is something to measure. In other words, in the system diagram shown in Figure 3, the f from the original sound source L is collected by the microphone 2, transmitted (including recording and playback) by the t* signal transmission system (sound equipment) 3, and transmitted to the speakers and heads 7 and 1.
5 converts the electrical signal into sound, which is perceived as sound by the auditory system 6.

Therefore, the compensation thread 4 should mainly have the inverse time-frequency vs. delay time characteristic in the narrowband transmission system 3 and the auditory system 6, but in general, the auditory system 6 is Since the time frequency vs. delay time characteristic is poor, the compensation characteristic of the compensation system 4 is approximately the inverse characteristic of the auditory system 6.@G Examples Various circuits are used as a compensation system that can achieve the above object. Although there are several possible configurations, two examples will be described here.

(1) Spectrum analyzer type (brancher correction type) M
As shown in Figure 1, the band of the acoustic signal transmission system 3 is divided into 1 kN, and a delay line with a large delay time is inserted into the high frequency component.
By synthesizing the lowest frequency component without the delay line t, it is given a frequency-delay time characteristic opposite to that of the auditory sense.

The input signal shown in FIG. 1 is divided into N frequency bands by an i divider 7. At this time, a linear axis and a logarithm S may be used as the frequency axis, but N may be smaller in the latter case. τ1. τ2
．． . . , τ indicates the delay time of the delay circuit 8, and is assumed to be a distribution that compensates for the frequency-delay time characteristic of the @electronic result 6.

Is this method an M extension? There are five major advantages to using a tap (and adjusting the delay time while listening to the playback sound to achieve the best overall characteristics).

(2) Active all-pass circuit type It is also possible to use a circuit used in a spectrum distribution display device of a subcircuit for the duplexer 7 shown in FIG. At this time, it goes without saying that adding the l-N components covers all the frequency components of the input signal.

Active all-pass circuits are based on Morishita and Mano, 11. Amplitude distortion and its compensation in active all-pass circuits, Proceedings of the Communications Society of Japan.
70/12, Vol 53-A, A12.
As described in E)-Q-687-693 (1976), this circuit has a flat frequency-regression characteristic and a delay time that changes with frequency. One of the circuits 1lfJ
'a' Shown in Figure 2. The frequency-delay time characteristic shown in FIG. 2(b) is determined by the constant of impedance Za in FIG. 2(aJ).

If the shape of the frequency-delay characteristic is the same as the shape of the auditory characteristic, one stage of delay time is sufficient, and if there are insufficient stages, several stages may be connected in series.

This method has the advantage of continuity over methods using frequency division and delay circuits.

If a medium wave AM receiver has a radio frequency amplification stage or an intermediate frequency stage, compensation may be made at this stage if the same effects as those described above can be achieved.

In this case, it is advantageous to make the delay time 11Jj of the upper sideband wave and the lower sideband wave equal to each other as much as possible with respect to the center frequency. Further, for example, if compensation at the intermediate frequency stage is easy, the circuit configuration can be simplified by compensating only the insufficient compensation amount at the audio stage.

As explained in detail in the invention, sounds that pass through a narrowband signal transmission system such as medium-wave AM often lack audible impact, but according to the present invention, the frequency is physically reduced, including the auditory system. Since it is possible to hear the sound without delay caused by the components, there is an advantage that the rise of the complex sound is improved and the impact is increased.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of the branching type compensation circuit according to the present invention, Figure 2 is a diagram showing an active all-pass circuit, Figure 3 is a system diagram of the sound source-transmission system - auditory system, and Figure 4 is a diagram showing the fundamental wave and A composite waveform diagram of the third harmonic; FIG. 5 is a diagram showing an example of auditory frequency-delay time characteristics; and FIG. 6 is a diagram showing changes in waveform due to square wave transmission characteristics. l... Original sound source, 2... Microphone, 3... Acoustic signal transmission system <H sound equipment), 4... Compensation system, 5... Speaker, headphones, 6... - Hearing system, 7 ... splitter, 8.
...Delay circuit group, 9...Adder, 10...Output. Bingsong ＼Saka Tomasa

Claims (3)

[Claims] (1) (a) A narrowband transmission system characterized in that it is provided in an acoustic signal transmission system that transmits an acoustic signal to the auditory senses through a speaker, and includes a compensation means that changes the delay time according to the frequency in the audible range. Sound quality compensation circuit. (2) The compensation means includes (a) a filter that divides the signal into a plurality of different frequency bands; (b) a delay line provided corresponding to the plurality of outputs of the filter and having a delay time corresponding to each frequency; and (c) means for adding the outputs of these delay lines. 2. The sound quality compensation circuit for narrowband transmission system according to claim 1, further comprising means for adding the outputs of these delay lines. (3) The sound quality compensation circuit for a narrowband transmission system according to claim 1, wherein the compensation means is composed of a single active all-pass circuit or a plurality of active all-pass circuits connected in series.