JPH0554727B2 - - Google Patents

Description

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

[Prior Art] Conventionally, in acoustic signal transmission systems, compensation for phase characteristics (vs. frequency) has hardly been performed.
The basis for this is that human hearing has almost no sensitivity to phase. For example, the synthesis of the fundamental wave and its third harmonic is as shown in Figure 4. In Figure 4 a and b, the phases of the fundamental wave and the third harmonic are different, but the difference in auditory perception is small. It is known.

However, in recent years, physiological and psychological research on hearing has progressed, and the temporal frequency vs. delay time characteristics of hearing have come to be measured.

Figure 5a is an example of a physiological experiment on cat hearing (de Boer: “Synthetic whole-nerve action”).
potentials”J.Acoust.Soc.Am., Vol 58.No.5,
(See PP1034) Nov. 1975), Figure b 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 the signal with the waveform a in FIG. 4 is perceived as the signal with the waveform b.

In a broadband acoustic signal system, the above-mentioned auditory phase characteristics need not be taken into consideration much. For example, when listening to the original sound directly and when listening to the sound of a wideband signal system, it is common that the magnitude of the frequency components hardly changes, and the low frequency components are heard with a delay, especially when the phase characteristics of the signal system are changed. There's no need to do it.

[Problems to be Solved by the Invention] However, in a narrowband transmission system, the high frequency components of the signal are naturally absent or attenuated, making it far from faithful reproduction of the original sound. This is why medium wave AM radio sounds less crisp than FM radio. That is, when the reproduced sound of the conventional narrowband transmission system is transmitted through the auditory sense, the waveform has a poor rise as shown in FIG. 3b.

An object of the present invention is to provide a compensation circuit that can improve the sound quality of a narrowband acoustic signal transmission system.

[Means for Solving the Problem] In order to achieve the above object, a sound quality compensation circuit for a narrowband transmission system according to the present invention combines an acoustic signal transmission system that provides an acoustic signal to the auditory senses via a speaker or a headphone, and the speaker or The object of the present invention is to include a compensating means which is provided between the headphone and the audible range and whose delay time changes depending on the frequency and which has at least a characteristic opposite to the time-frequency-delay time characteristic in the auditory system.

The compensation means includes a filter that divides a signal into a plurality of different frequency bands, a delay line provided corresponding to the plurality of outputs of the filter and having a delay time corresponding to each frequency, and outputs of the delay line. means for summing, or one or more cascaded active all-pass circuits.

[Operation] The acoustic signal from the transmission system is compensated by the compensation means with characteristics opposite to those of the auditory system, and this compensated sound is perceived by the auditory system.

The compensation is performed, for example, by a duplexer-type compensation circuit or an active band pass circuit.

[Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 3 is a system diagram showing one embodiment of the present invention.
2 is an original sound source, 2 is a microphone, 3 is an acoustic signal transmission system (acoustic equipment), 4 is a compensation system, 5 is a speaker or headphone, and 6 is an auditory system.

FIG. 6 shows an example c in which a 50 Hz square wave original sound a is passed through a narrowband transmission system and a waveform b, and a compensation circuit is provided for the state of b. Here, for convenience of calculation, it is assumed that up to the ninth high frequency passes as a narrow band.
The compensation circuit of c is the auditory frequency shown in Fig. 4b.
It was made to have an inverse characteristic of delay time.

As is clear from comparing Figure 6 c and b, c
The rise of the waveform is better in case b than in case b. In other words, the rise in response to more or less shocking sounds is improved. In other words, the rise of the waveform is de/dt
(de/dt) _(c) > (de/dt) _(b) The present invention compensates the frequency-delay time characteristics even in the case of narrowband transmission systems (audio equipment), and improves the auditory rise. The purpose is to supply a good signal tone and improve the sound quality. For example, in the embodiment of FIG. 3, the sound emitted from the original sound source 1 is collected by the microphone 2, and transmitted (including recording and playback) by the audio signal transmission system (acoustic equipment) 3,
The electrical signal is converted into sound by a speaker or headphone 5 via a compensation system 4, and is perceived as sound by an auditory system 6.

Therefore, the compensation system 4 should mainly have an inverse time-frequency-delay time characteristic in the narrowband transmission system 3 and the auditory system 6, but in general, the auditory system 6 is more sensitive than the acoustic signal transmission system 3. Since the time frequency-delay time characteristic is poor, the compensation characteristic of the compensation system 4 is approximately the inverse characteristic of the auditory system 6.

Although various circuit configurations can be considered as a compensation system that can achieve the above object, two examples will be described here.

(1) Spectrum analyzer (brancher correction type) As shown in Figure 1, the band of the acoustic signal transmission system 3 is divided into N parts, and a delay line with a longer delay time is inserted for higher frequency components, and the lowest frequency component is delayed. By composing the signals in a line, a frequency-delay time characteristic opposite to that of the auditory sense is created.

The input signal shown in FIG. 1 is divided into N frequency bands by a duplexer 7. In this case, a linear axis and a logarithmic axis may be used for the frequency axis, but the latter is better for N
can be small. τ ₁ , τ ₂ , _.

This method has the advantage that if the delay line is provided with a tap, the delay time can be adjusted while listening to the reproduced sound to obtain the overall optimum characteristics.

(2) Active all-pass circuit type It is also possible to use a circuit used for a spectrum distribution indicator of an acoustic circuit for the duplexer 7 in FIG. At this time, it goes without saying that by adding the components 1 to N, all the frequency components of the input signal are covered.

Active all-pass circuits are described, for example, by Morishita and Mano,
“Amplitude distortion and its compensation in active all-pass circuits” Journal of the Communications Society of Japan, 70/12, Vol.53-A, No.12, p.
As described in p. 687-693 (1976), this circuit has flat frequency-amplitude characteristics and a delay time that varies with frequency. An example of the circuit is shown in FIG. The constant of the impedance Za shown in FIG. 2a determines the frequency-delay time characteristic shown in FIG. 2b.
If the shape of the frequency-delay time characteristic is the same as the shape of the auditory characteristic, one stage of delay time may be sufficient, but if it is insufficient, several stages may be connected in series.

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

In cases where a medium-wave AM receiver has a radio frequency amplification stage or an intermediate frequency, compensation may be performed at this stage as long as equivalent effects similar to those described above can be obtained.

In this case, it is advantageous to make the delay times of the upper and lower strips as equal 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 if only the insufficient compensation amount there is compensated for at the audio stage.

[Effects of the Invention] As explained above, sound that passes through a narrowband signal transmission system such as medium-wave AM often lacks audible impact, but according to the present invention, the frequency is physically reduced, including the auditory system. Since it is possible to listen to sound without delay due to components, there is an advantage that the rise of the complex sound is improved and the impact is increased.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a branching type compensation circuit as an example of the compensation means in the present invention, FIG. 2 is a diagram showing an active all-pass circuit as another example of the compensation means, and FIG. 3 is a circuit diagram of the present invention. A system diagram of one embodiment, FIG. 4 is a composite waveform diagram of the fundamental wave and third harmonic, FIG. 5 is a diagram showing an example of auditory frequency-delay time characteristics, and FIG.
The figure is a diagram showing changes in waveform due to the transmission characteristics of a square wave. 1... Original sound source, 2... Microphone, 3... Acoustic signal transmission system (acoustic equipment), 4... Compensation system, 5... Speaker, headphone, 6... Auditory system, 7... Duplexer, 8 ...Delay circuit group, 9...Adder, 10...
output.

Claims (1)

[Scope of Claims] 1. At least the auditory device, which is provided between an acoustic signal transmission system that provides an acoustic signal to the auditory senses via a speaker or a headphone, and the speaker or headphone, and whose delay time changes depending on the frequency of the audible range. 1. A sound quality compensation circuit for a narrowband transmission system, comprising compensation means having an inverse time-frequency-delay time characteristic in the system. 2. The compensation means includes a filter that divides a signal into a plurality of different frequency bands, a delay line that is provided corresponding to the plurality of outputs of the filter and has a delay time corresponding to each frequency, and a 2. A sound quality compensation circuit for a narrowband transmission system according to claim 1, further comprising means for adding outputs. 3. The sound quality compensation circuit for a narrowband transmission system according to claim 1, wherein the compensation means comprises a single active all-pass circuit or a plurality of active all-pass circuits connected in series.