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The present invention relates to audio signal processing systems, and more particularly to defect
compensation apparatus useful for such systems. In an audio system such as a transmission
system, a recording / reproducing system, or a system in which a carrier wave is frequencymodulated by an audio signal, occasional impulse noise may be introduced into the carrier wave
over time, in a wide band. In addition, there is partial or total attenuation of the carrier (referred
to as carrier loss), and in such a case, when the defective carrier is regenerated, the audio signal
is also attenuated accordingly. In a system in which a carrier wave signal modulated according to
audio information is reproduced by a conversion element, any one of a recording medium, a
conversion element, or any of a cooperative relationship between the recording medium and the
conversion element, for example, during reproduction of recording information. Inadequacies can
sometimes cause loss of carrier and impulse noise. For convenience, the invention will be
described in connection with a video record recording and reproducing scheme of the type
described in US Pat. No. 3,842,194 of Clemens. In the method disclosed in the above-mentioned
Klemens patent specification, the recorded information is expressed in the form of a geometrical
change of the bottom of the drawing groove provided on the surface of the disk-like substrate,
and the surface is covered with a conductive film. It is further covered with a dielectric layer.
There is a housing which is driven in the radial direction with respect to a turntable which
mounts and rotates the record board, and a pickup needle is supported by a pickup arm mounted
in the housing. The needle has an electrode that forms an electric capacitance with the coating of
the disk, and when the disk rotates, its capacity fluctuates according to the geometrical change of
the groove bottom passing under the electrode. A suitable circuit coupled converts the
capacitance variation into a change in the electrical signal representing the recorded information.
A desirable version of the above Clemens system is described in Keizer US Pat. No. 3,911,476,
wherein the first carrier frequency modulated according to the video information is a series of
maximum depths at the groove bottom. The second carrier (which has a significantly lower
frequency than the video information carrier) frequency-modulated according to the audio signal
for monophonic audio reproduction, preferably in the form of an alternating cycle of The voice
information is represented in the form of impulse coefficient modulation (the ratio of the
maximum depth or the minimum depth in each cycle, ie, the proportion of the impulse coefficient
in accordance with the information) in each alternating cycle. As described in detail in U.S. Pat.
No. 3,969,756 to Palmer et al., Video information includes multi-channel audio information (e.g.,
stereo サ ウ ン ド sound 2 track, bilingual sound track, etc.) If it is desired to attach), the method
by the above-mentioned impact coefficient modulation is suitable for this.
Since each audio signal is modulated and recorded over different low frequency deviation ranges
of different audio carrier frequencies, the duty cycle of the video information carrier changes in
accordance with the sum of each audio carrier. As an example of application of the principle of
the present invention, when providing a pair of audio channels to form a stereo configuration,
the center frequencies of the audio carrier are selected to 715.909 KH2 and 904.720 KHz, and
the deviation range is centered on each center frequency. Choose ± 50 KHz. A player for a video
record of the type described above comprises a plurality of FM demodulators with suitable input
filter stages, for example for reproducing carrier signals or audio signals and video signals
respectively obtained by the player; A problem that arises in the reproduced sound (if it is not
compensated) is that "tick J sound or" pop J "is reproduced intermittently at irregular intervals
instead of the appropriate audio information. There are disturbances in the form of sound, which
can lead to carrier loss and impulse noise defects, respectively. These flaws are not harmful to
audio information as a whole, but can be a nontrivial obstacle to the viewer. Analysis of the
problem has shown that in the above-described video record player, each audio defect causing
the interference is caused by various causes. Some of the causes are related to defects in the
record itself, and others are encountered during a specific reclamation operation of a given
record (for example, a needle encounters dust of various shapes at various places in the record
groove) And others (e.g., scratches, pits, etc.) relate to how much of the playing record has been
used or misused in the past. Although the cause of the audio defect is not described in further
detail, it is obvious that there are various causes which are highly non-predictive and cause a
change problem if the recording disk, the reproduction time, the groove area or the like changes.
According to an embodiment of the invention, an audio processing channel is provided, wherein
the audio signal derived by the demodulator from the frequency modulated carrier signal being
recorded for reproduction is "track J" or "hold". And J) is supplied to the utilization device
through a track and hold amplifier that can operate in any of the three molds. Separate detection
means are provided for detecting carrier loss and broadband impulse noise respectively, and
each output of this detection means triggers each monostable multivibrator forming part of the
control pulse generation circuit to perform track and hold. The amplifier is switched to each
The duration of the control pulse is chosen such that the amplifier is kept in the "hold" mode
until the temporary defects at the input of the track-hold amplifier have been eliminated
sufficiently. As a modification of the above embodiment, in another embodiment of the present
invention where reproduction other than monaural sound is expected, an audio processing
channel of another bone similar to the above described audio processing channel can be
provided for each sound carrier. In the multi-channel embodiment of the present invention
having a common voice carrier (e.g. multiplexed signal) source, any one carrier defect is mostly
reproduced also in the other carrier and generated in its audio processing channel. Control
pulses are used to control the switching of each track and hold amplifier of the other audio
processing channel, so that the defect detection means and the control pulse generation means
are only one of the plurality of audio processing channels. It has the feature that only one needs.
Further, according to the present invention, each audio processing channel is provided with a low
pass filter circuit, and the signal de-emphasis is performed on the high frequency component so
as to supplement the pre-emphasis of the high frequency component of the audio signal. It is
designed to reduce the noise added to the fist hold amplifier. In addition, two low pass filters are
separately used to provide a de-emphasis function in order to obtain both of the above effects by
using inexpensive elements. A first low pass filter is coupled between the output of the
demodulator and the input of the track and hold amplifier, and the output of the track and hold
amplifier is coupled to the audio signal utilization circuit via a second low pass filter It is done. It
is desirable that the total response of the first and second low pass filters provide the desired deemphasis on the signal being processed on that channel, and that the total response be flat over
the entire bandwidth of the audio signal. However, it is important to note that the noise
transmitted to the input of the track and hold amplifier is reduced because the passband width of
the first low pass filter is narrower than the bandwidth of the output of the demodulator, and the
track and hold amplifier Is the probability of holding the noise signal is reduced. The present
invention will be described in detail with reference to the accompanying drawings. In the video
record player shown in FIG. 1, the input signal of the signal processing circuit of the player is
generated terminally by the video record pickup circuit 11. This video record pick-up system is
of the capacitive type described above, and the structure and circuit configuration of the device
are described in the aforementioned Pall 1 U.S. Patent.
The recording format of the reproduction recording disc is that the reproduction signal
information appearing at the terminal is a high frequency pulse train which changes in
accordance with the amplitude of the recorded composite color video signal, and this pulse train
corresponds to the amplitude of the recorded audio signal. It is therefore assumed that at varying
frequencies (each significantly lower than the above-mentioned high frequencies), it has a
periodically changing shock factor centered around 0.5. The wideband pre-amplifier 13 amplifies
the impulse coefficient modulated pulse train and supplies it to the inputs of the four band pass
filters The band pass filter 15 has a relatively wide pass band including the
deviation range of the high frequency video carrier (fp) and the necessary sidebands adjacent to
each other, and removes the audio carrier component of the recorded signal to remove the video
carrier component. Is selectively passed (the pass band of this film 15 is, for example, 1.3 MHz to
9.3 MHz), the output of the band pass filter 15 works to remove the unnecessary amplitude
change of the carrier 23 (carrier useless ) To the demodulator 24. It will be apparent to those
skilled in the art that the scheme of FIG. 1 is for stereo sound reproduction including two audio
processing channels 25 and 26 and that in monaural sound reproduction scheme channel 25
may be eliminated. Conversely, if three or more channels are required, the same channel as
channel 25 may be added, and in some cases, it is necessary to design a multi-channel audio
reproduction system provided with detection means for dropout and impulse noise in each
channel. Of course. However, in most cases where voice carriers for multi-channel audio
reproduction are used, carrier loss and impulse noise defects commonly occur in all channels as
described above, and only one detection means is required for each defect. Thus, the above
design often results in unnecessary duplication of circuitry. The channel 25.26 shown in FIG. 1 is
a band pass filter with a relatively narrow passband including the deviation range of the low
frequency speech carrier! ? , 2! Contains each. The band pass filter 17 has a passband centered
on the voice carrier center frequency fs above 904.720 KHz and this bandwidth covers all of the
primary and secondary sideband components of the upper voice carrier modulated. It is
sufficiently wider than the upper voice carrier deviation range (eg f $ ± 80 KHz) to ensure
passage. The band pass filter 21 also has a passband centered at the voice carrier center
frequency fs' below 5.509 KHz, this bandwidth being the primary and secondary sideband
components of the modulated lower voice carrier. Are sufficiently wider than the lower voice
carrier deviation range (e.g. fs'. ± .80 KHz) to ensure that all of them pass through.
The output of the band pass filter 17 is supplied to the limiter 27 and the output of the band
pass filter 21 is supplied to the limiter 31 via the amplifier 29 (both limiters 27.31 have the
disadvantage of the frequency modulated voice carrier components). The outputs of the limiters
31.27 are respectively fed to the frequency modulation demodulator 35.37. The reason for
amplifying and gain controlling the output signal of the band pass filter 21 is that carrier loss is
detected in the channel 26, which will be described in detail later. In the audio processing
channel 25.26, the demodulator 35.37 generates a signal output corresponding to each recorded
audio signal at each of the output terminals v and W, and this output is a low pass filter 39.41
(described later) To de-emphasis the audio signal and to reduce power supply noise), and then
supplied to the track and hold amplifier 43. 45. Track-and-hold amplifier 43.45 is a circuit
having a "track" mode and a "hold" mode, which when in "track" mode produces an output
exactly (ideally) to the input and thus proportional to the input When in the "hold" mode, the
control pulse is commanded to maintain the output at a constant value (ideally) appearing at the
moment of transition from the "track" mode to the "hold" mode. (The output of the track ホ ー ル
ド hold amplifier 43. 45 is connected to the low pass filter 39. 41 to de-emphasis the audio
signal, respectively. Through an interface) to a suitable audio utilization device 51.53 of known
type, so that the reproduced audio signal can be used for a sound device. When the voice carriers
fs and fs' are processed by each demodulator, the output signal of each demodulator may be
delayed by several microseconds, in which case the detected defect is controlled to appear at the
output of each demodulator By taking advantage of this inherent delay in the demodulator, which
causes the track-and-hold amplifier to be switched to the "hold" mode by the pulse, there is no
transient reduction in the audio output of the track-and-hold amplifier. Although the above
description of the illustrated apparatus is for the player's operation in normal conditions,
consider now a working mode suitable for effective compensation or occultation of audio defects.
The recognition of the onset of a signal defect that dictates the change of the operating mode of
the audio processing channel is by the function of the defect detection circuit 55.
In accordance with the defect detection principle of the present invention, this detection circuit
55 comprises a wide band filter including a band pass filter 19 (for example with a pass band of
± 80 KHz width centered on the center frequency fn) coupled to the signal output of the wide
band preamplifier 13 An impulse noise detector is provided. The band pass filter 19 has the same
bandwidth as the signal band pass filter 17.21 and also has the same low pass prototype as that
of the impulse response and the same as the envelope of the impulse response of the filter 17.21.
It is supposed to be in This band pass filter 19 should occupy a spectral range relatively free of
modulated carrier components, and preferably no other signal energy, for example in the range
of fn = 500 KHz, and the center frequency of the band pass filter 19 Phil pl? , 21 as close as
possible to the center frequency, so that the energy of the noise impulses in the band should be
almost equal. The relationship between the passband of the filter 19 and the passband of the
filter 17.21 is shown in the diagram of FIG. The output of the band pass filter 19 is amplified by
an amplifier 56 whose output is grounded via a series circuit of a potentiometer 57 and a
capacitor 59. The sliding arm 61 of the potentiometer 57 is coupled to a retriggerable
monostable multivibrator (for impulse noise) 63 having a period equal to the inverse of the
lowest frequency of the output of the impulse noise band pass filter 19. The output of the band
pass filter 19 is amplified and gain controlled such that the monostable multivibrator 63 can be
triggered by a ringing level comparable to a standard voice carrier component level above a
predetermined threshold. The output of the monostable multivibrator 63 occurring at the
terminal X therefore corresponds to the logic level "1" whenever the ringing of the impulse noise
band-pass filter exceeds a predetermined threshold. The output of the signal band pass filter 21
of the carrier dropout detecting means is amplified by the amplifier 29 and gain controlled by
the potentiometer 33 so that the output appearing on the sliding arm 65 is a predetermined
fraction of the normal signal level. Some percentage will trigger a retriggerable monostable
multivibrator (for missing carrier) 67. The output of monostable multivibrator 67 is a carrier
band pass filter since one cycle of the output of monostable multivibrator 67 for lack has a value
equal to the inverse of the lowest frequency of the output signal of signal band pass filter 21
based on the normal signal. Corresponds to a logic level "0" whenever it falls below a
predetermined fraction of the normal signal level, and to a logic level "1" otherwise.
Conversely, the inverted output of multivibrator 67 (at each other) generated at terminal Y
corresponds to logic level "l" whenever the carrier band pass filter output falls below a
predetermined ratio of the normal signal level, and the other The time corresponds to the logic
level "0". The output of the monostable multivibrator for impulse noise and the inverted output of
the missing monostable multivibrator are the first NORAGE where the output becomes a logic
level “1” when there are no signal inputs at the two input terminals X and Y) 69 Are
respectively supplied to the two input terminals of The output of NOR gate 69 is always "O" if the
input signal at either terminal X, Y corresponds to logic level "l", and inverter 71 and
retriggerable monostable multi-channel having a predetermined duration. The output of the 0
inverter 71 supplied to the vibrator (stretching set) 73 and the output of the monostable
multivibrator 73 for stretching are supplied to the two input terminals of the second NOR gate
75 respectively. 71, a monostable multivibrator 73 and a second NOR gate 75 act as a pulse
puller which extends the duration of the output pulse of the first NOR gate 69, and the defect
detected at the track and hold increase #A 塁 input Transients based on V.sub.2 will disappear
fully and reliably before the amplifier returns to "track" mode of operation. The output of NOR
gate 75 applied to each control input S of track and hold amplifier 43.45 normally corresponds
to a logic level "1" which keeps the track and hold amplifier in "track" mode, but a defective pulse
is detected It will always be "0" and the amplifier will be switched to "hold" mode for the duration
of the control pulse. The function of the de-emphasis means used in the embodiment of the
present invention shown in FIG. 1 will now be described. The power supply noise is as low as
possible while the transient response to the defect is not stretched as much as possible by the
action of the first low pass filter. Also, the overall response of the first and second low pass filters
needs to include the required audio processing channel de-emphasis, but on the other hand must
be flat over the required bandwidth. If the bandwidth of the first low pass filter is very wide, the
stretching time of the control pulse required to prevent transient defects can be greatly reduced
and the loss of audio information is minimized, but the track ホ ー ル ド hold The power supply
noise level at the amplifier input is so high that the amplifier does not eventually maintain the
required signal value, but maintains a random noise impulse value.
On the other hand, if the bandwidth of the first low pass filter is too narrow, the maintenance of
its random noise impulses will be very slight, but the control pulse stretching time required to
prevent transient defects will be longer Because there is more loss of information, a compromise
must be made between the amount of filtering for noise reduction and the stretching time
required for the occultation of the resulting transient defects. When using the audio channel of
the above-described capacitive video record player, a control pulse duration of 28 microseconds
and a 3-terminal Butterworth 17 KHz low pass preretention filter are suitable for power supply
noise reduction and transient defect concealment Is known to In the embodiment of the present
invention, a record board has been mentioned as a specific example of the recording material on
which the information to be reproduced is recorded, but the shape of the recording material is
not specified as a disc but a tape etc. Needless to say, it may be in the form of
Brief description of the drawings
FIG. 1 is a block circuit diagram of a video record player apparatus incorporating a defect
compensation method according to one embodiment of the present invention, and FIG. 2 is a
chart showing frequency bands related to various signal components of the apparatus of FIG. .
11 Record player φ pickup device 17.19.21 Band pass filter 25.2 audio processing channel
35.57 potentiometer potentiometer 35.37 FM demodulator , 43.45 ... track and hold amplifier,
63.67.73 ... monostable multivibrator, 69,? 5 · · · NOR gate, 71 · · · inverter.
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description, jph02139766
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