JPH0451914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an audio signal processing device suitable for use in connecting and editing audio signals.

Prior Art and its Problems In editing work, which involves recording audio signals (used herein to mean audio frequency signals) on magnetic tape, etc., and later deleting unnecessary parts and connecting only the necessary parts. , in order to avoid sudden changes in the amplitude and frequency spectrum of the audio signal at the connection point, the amplitude of the audio signal S _A on the rear side is gradually decreased (fade out) while the amplitude of the audio signal S _B on the front side of the connection point is decreased (fade out). A cross-fade that gradually increases (fade-in) is performed. Usually, this crossfade is
It is performed in a short time of about 10 to 30 mS. If this time becomes longer, the two sounds may be perceived as overlapping, leading to a sense of discomfort.

However, when connecting low-frequency audio signals,
If the phases of the audio signals before and after the connection point are significantly different, the instantaneous amplitude of the audio signals before and after the connection point will change rapidly in the short-time crossfade process described above, resulting in click-like noise that does not exist in the original audio. There was a problem with abnormal noises.

OBJECTS OF THE INVENTION In view of the above, an object of the present invention is to provide an audio signal processing device that can reduce the occurrence of abnormal noise during crossfade processing.

Composition of the Invention The present invention provides an audio signal processing device that connects one audio signal and the other audio signal by gradually decreasing the level of one audio signal and gradually increasing the level of the other audio signal. The first crossfade means 12, 22 crossfade by gradually decreasing the audio signal SA while gradually increasing the other audio signal SA, and extract high frequency components from both audio signals SB, SA, respectively, and crossfade at a higher speed than the first crossfade means 12, 22. second crossfade means 15, 25, 13, 23, 14, 24, and first and second crossfade means 12, 22 and 1
This is an audio signal processing device characterized in that it is equipped with an adding means 30 for adding the outputs of signals 5, 25, 13, 23, 14, and 24, and performs cross fading.

Embodiment Hereinafter, an embodiment of the audio signal processing device according to the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the present invention. In FIG. 1, numerals 10 and 20 are fade circuits having variable frequency characteristics, and since both fade circuits 10 and 20 have the same configuration, corresponding elements are denoted by the same number as the first digit. The structure of one of the fade circuits 10 will be explained as a representative, and the explanation of the other one will be omitted.

Reference numerals 12, 13, and 14 are voltage-controlled variable gain amplifiers, and 15 is a voltage-controlled variable characteristic high-pass filter, in which the audio signal S _B from the input terminal 11 is directly supplied to the amplifier 12, and the high-frequency The signal is supplied to the amplifier 13 via the filter 15, and further to the amplifier 14 via the high-pass filter 15 and inverter 16. The outputs of amplifiers 12-14 are supplied to adder 17 and added.

Then, the audio signal S _A is supplied to the input terminal 21 of the fade circuit 20, and the fade circuit 1
0 adder 17 and adder 2 of fade circuit 20
7 are supplied to an adder 30 and added together,
The addition output is derived to the output terminal 31.

32 is a control signal generator that generates a control signal for controlling both the fade circuits 10 and 20, and the control signal from this is sent to the amplifiers 12 and 22, and the control signal is sent to the amplifiers 13 and 2.
4, control signals are supplied to amplifiers 14 and 23, and control signals are supplied to high-pass filters 15 and 25, respectively.

Next, the operation of this embodiment will be explained with reference to FIGS. 2 to 5.

The gain (normalized gain) of the amplifier 12 to which the control signal from the control signal generator 32 is supplied is 1 before time _t1 , as shown in FIG. 2A, and linearly increases as time passes thereafter. The value decreases and reaches 0 at time _t9 . Further, contrary to the above, the gain of the amplifier 22 to which the control signal is supplied is 0 before time _t1 , increases linearly thereafter, and reaches time _t9 , as shown in FIG. 2B. It becomes 1. Note that the sum of the gains of both amplifiers 12 and 22 is 1 at any given time.

The gains of the amplifiers 13 and 24 to which the control signals are supplied increase, as shown in FIG. 2C, from time t ₁ to t ₄ at the same rate as in FIG _. As in case B, it becomes 3/8, and after that it decreases and reaches 0 at time _t5 . Furthermore, the gains of the amplifiers 14 and 23 to which the control signals are supplied increase from 0 at time _t5 , as shown in FIG. 2D, and become 3/8 at time _t6 , the same as in FIG. 2A. , after that it decreases at the same rate as in the case of Figure 2 A,
It becomes 0 at time _t9 .

The cut-off frequencies of the high-pass filters 15 and 25 are determined by control signals at certain times as shown in FIG. 2E.
It increases linearly from ₁ at time t ₁ to ₅ at time t ₅ and then decreases linearly to become ₁ again at time t ₉ .

As mentioned above, the amplifier 12 of the fade circuit 10
Since the gain of ~14 and the cutoff frequency of high-pass filter 15 change with time, the outputs of amplifiers 12, 13, and 14 can be expressed as A(t), C(,t), and D(,t), respectively. Therefore, the output F ₀ of the fade circuit 10 is expressed as the following equation (1).

F ₀ =A(t)+C(,t)-D(,t)...(1) Similarly, the amplifiers 22 and 23 of the fade circuit 20
and the outputs of 24 are B(t), D(,t) and C
(, t), and the fade circuit 2
The output F _i of 0 is expressed as the following equation (2).

F _i =B(t)+D(,t)-C(,t)...(2) For example, at time _t3 , A( _t3 )=3/4,
B(t ₃ )=1/4. Furthermore, as can be seen from Fig. 2E, the cutoff frequency of the high-pass filter 15 at time _t3 is ₃ , so the normalized amplitude of C(, _t3 ) is 1/4 in the frequency range of ₃ or higher. . This is C
(, t ₃ )=1/4( ₃ ), then D(+t ₃ )
=
0, so both fade circuits 10 at time _t3
The outputs F ₀₃ and F _i3 of 20 and 20 are as follows, respectively.

F ₀₃ = 3/4 + 1/4 ( ₃ ) ... (3) F _i3 = 1/4 - 1/4 ( ₃ ) ... (4) That is, the fade circuit 10 has an amplitude of 3/4 above the reference amplitude over the entire frequency range. Standard amplitude 1/4 when frequency is ₃ or more
It has a characteristic that is like a stack of . On the other hand, the fade circuit 20 has a standard amplitude of 1/4 when the frequency is below ₃ .
Above ₃ , there is no output.

Both fade circuits 10 and 2 at times t ₁ to _{t 9}
The output (frequency characteristics) of 0 is shown in Figure 3. As is clear from Fig. 3, at any time and at any frequency, the outputs F ₀ and F _i of both fade circuits
The sum of is constant.

Furthermore, the output signals F _ph , F pl , F _pl ,
The amplitudes of F _ih and F _il change as shown in FIG. 4 from time t ₁ to _{t 9} . In other words, for high-frequency signals with a sufficiently short cycle compared to the 10-30mS crossfade period mentioned above, the crossfade period is 10-30ms as before.
It performs crossfade processing at extremely high speed in a short time, and for low-frequency signals with a period that cannot be ignored compared to the conventional short crossfade period,
Perform a longer crossfade process. Therefore, 2 having the phase relationship as shown in FIG. 5A
When two audio signals S _B and S _A are connected, as shown in FIG. 5B, the connection can be made smooth to reduce the occurrence of abnormal noise.

Although a voltage-controlled variable characteristic high-pass filter is used in the above-described embodiment, the input signal may be divided into a plurality of frequency bands by a plurality of filters, each having a different crossfade time. Furthermore, it is also possible to obtain the same effects as in the above-described embodiments by using a digital filter.

Effects of the Invention As detailed above, according to the present invention, the crossfade period is changed depending on the frequency of the audio signal, and the crossfade period of the high frequency audio signal is comparatively about 10 to 30ms, which is the same as before. Since the crossfade is carried out at high speed and the crossfade period of the low-frequency audio signal is lengthened, the generation of abnormal noise accompanying the crossfade processing can be reduced and the crossfade output can be made smooth.

[Brief explanation of the drawing]

1 and 2 are block diagrams and time charts showing one embodiment of an audio signal processing apparatus according to the present invention, and FIGS. 3 to 5 are diagrams for explaining the present invention. 12, 13, 14, 22, 23, 24 are voltage controlled amplifiers, 15, 25 are voltage controlled high-pass filters,
32 is a control signal generator.

Claims (1)

[Scope of Claims] 1. In an audio signal processing device that connects one audio signal and the other audio signal by gradually decreasing the level of one audio signal and gradually increasing the level of the other audio signal, a first crossfade means that gradually decreases one signal and gradually increases the other audio signal for crossfade; and a second crossfade means that extracts high-frequency components from each of the two audio signals and crossfade them at a higher speed than the first crossfade means. ,
An audio signal processing device for crossfading, comprising an adding means for adding the outputs of the first and second crossfade means.