GB2150734A - Inter-music interval detecting system and method - Google Patents

Abstract

An inter-music detecting method and system in which the presence of inter-music intervals in a digitized audio signal superposed on a video format signal is positively detected. When the audio signal is recorded, the synchronizing signal is muted for periods corresponding to the inter-music intervals. For reproducing the audio signal, inter-music intervals are detected by sensing the absence of the synchronizing signals in the reproduced audio signal. <IMAGE>

Description

SPECIFICATION Inter-music interval detecting system and method The present invention relates to inter-music interval detecting methods and systems. and more particularly to an inter-music interval detecting method and system for an audio data PCM (Pulse Code Modulation) processor such as may be used in a VTR (Video Tape Recorder).

In a PCM processor for consumer use. an audio signal such as a music signal is converted into a digital signal using a PCM system. The synchronizing signal of a composite video signal is added to the digital signal to obtain a so-called video format signal. The video format signal is then recorded on video tape.

In reproducing the audio data. the PCM signal is separated from the video format signal to thereby obtain a reproduced audio signal. In such a system. an intermusic interval can be detected by a method using the counter of the VTR or by a method utilizing the reproduced sound. In the former method.

the count value of the counter which occurs during inter-music intervals is read and recorded. and in the signal reproduction mode.

the inter-music intervals are detected by referring to the count value thus recorded. In the latter method. the fast-forward. rewind or picture-search key is operated so that the intermusic intervals can be detected while listening to the reproduced sound.

The method of using the counter is disadvantageous because the count value corresponding to the inter-music intervals must be known. On the other hand, the method of utilizing the reproduced sound is also disadvantageous in that during fast-forwarding the reproduced sound is considerably noisy.

Accordingly, an object of this invention is to provide an inter-music interval detecting method and system with which inter-music intervals can be readily and positively detected.

A specific feature of the inter-music method and system according to the invention resides in that, in recording digitized audio data on a predetermined recording medium in such a manner that the audio data is superposed on a video format signal, a part thereof which corresponds to an inter-music interval of the audio data is recorded with synchronizing signals omitted, and in reproducing the audio data, a part of a reproduced signal which has no reproduced synchronizing signal is detected thereby to detect the inter-music.

In the drawings: Fig. 1 is a block diagram of a preferred embodiment of an inter-music interval detecting system of the invention; Fig. 2 is a circuit diagram showing an example of a muting circuit in Fig. 1; Fig. 3 is a block diagram of a reproducing portion of an inter-music interval detecting system of the invention; Fig. 4 is a circuit diagram showing an example of a synchronizing signal detector in Fig. 3; and Fig. 5 is a waveform diagram showing operating waveforms in the device shown in Fig. 3.

The present invention will be described with reference to the accompanying drawings.

Fig. 1 is a block diagram showing a portion of an inter-music interval detecting system of the invention used for recording audio signals.

An audio signal, such as a music signal, to be recorded is converted into a digital signal by sampling by an A/D (Analog-to-Digital) converter 1. The output signal of the A/D converter 1 is subjected to pulse code modulation (PCM) by a PCM circuit 2. The output signal of the PCM circuit 2 is applied to a synthesizer 4 where it is combined with a synchronizing signal provided by a synchronizing signal generator 3 into a video format signal.

The video format signal is supplied as a recording signal to a recording and reproducing circuit 7 through a muting circuit 5. In the muting circuit 5, the video format signal is interrupted, i.e., application of the video format signal to the recording and reproducing circuit 7 is suspended, for the period of time that the muting switch 6 is turned on.

Fig. 2 shows an example of the muting circuit 5. A switching transistor Q,, connected between a video format signal line 8 and ground, is turned on and off by the muting switch 6. A bias voltage produced when the muting switch 6 is turned on is applied to the connecting point of resistors R, and R2 which are connected between the base of the transistor Q, and ground. When the muting switch 6 is turned on, the transistor Q, is rendered conductive (on) so that the signal line 8 is then at ground potential and application of the video format signal is interrupted.Accordingly, by turning on the muting switch 6 for an inter-music interval which occurs during the signal recording operation, application of the video format signal to the recording and reproducing 7 is suspended, and therefore neither of the PCM signal and synchronizing signal are recorded on the video tape.

Fig. 3 is a block diagram of the reproducing circuitry. The reproduction signal (A) outputted by the recording and reproducing circuit 7 (Fig. 1) is applied to a synchronizing separator circuit where only the synchronizing signal is extracted. The synchronizing signal (B) thus extracted is applied to a synchronizing signal detector 10 which provides an output signal (C) in an active state when the synchronizing signal (B) is absent. The detection output (C) is applied through a driver circuit 11 to an inter-music interval display unit 12.

Fig. 4 shows an example of the synchronizing signal detector 10 in Fig. 3. A synchronizing signal (B) is applied to the base of a transistor Q2 through a base biasing circuit composed of resistors R3 and R4. The collector output of the transistor Q2 is applied to a time constant circuit of a resistor R5 and a capacitor C1. The output of the time constant circuit is applied to a level comparator, namely, a differential amplifier A1, where it is compared with a reference level which is provided by a voltage divider circuit formed by resistors R6 and R7. The level comparison output of the amplifier At is the signal (C).

No active level comparison output is provided as long as the synchronizing signal is present. However, if no synchronizing signal is applied for the period of time which is determined by the time constant RsCt and the reference level, the level comparison output (C) is raised to the high level from the low level.

Fig. 5 is a waveform diagram for a description of the operation of the system shown in the block diagram in Fig. 3. More specifically, waveforms (A), (B) and (C) of Fig. 5 show the signals (A), (B) and (C) of Fig. 3, respectively.

If a video format signal recorded on the video tape has a lack of signal for a period of time T corresponding to an inter-music interval as seen in waveform (A), the reproduction signal has no synchronizing signal for the period of time T as shown in waveform (B).

Accordingly, the output signal of the detector 10 is as shown at (C) in Fig. 5. Therefore, whenever an inter-music interval occurs, the inter-music interval display unit 12 is driven to turn on a lamp or the like. Thus, the intermusic interval is positively detected and indicated.

As is apparent from the above description, according to the invention, in superposing the PCM signal on the video format signal, parts thereof corresponding to the inter-music intervals are omitted, and during signal reproduction, the parts which have no synchronizing signal are detected, thereby to detect the inter-mu4sic intervals. Thus, the inter-music intervals can be readily and positively detected.

Furthermore, an inter-music interval can be readily detected during fast4orwarding, rewinding or picture-searching, and therefore these operation can be achieved with the volume control turned down, with the result that the generation of noise is prevented.

In the above-described embodiment, the muting circuit 5 is provided at the rear stage of the synthesizer 4. However, only the synchronizing signal may be muted in the synthesizer. Furthermore, the inter-music interval detecting system may be so designed that, based on the fact that the level of the analog audio signal is lower than a certain value when an inter-music interval occurs, the video format signal or the synchronizing signal is muted for the corresponding period of time.

The arrangement of the synchronizing signal detector 10 is not limited to that shown in Fig. 4. For instance, it may be implemented with an oscillator having the same frequency as that of the synchronizing signal, wherein, when the frequency of the output signal of the oscillator does not coincide with that of the reproduced synchronizing signal, the lack of signal is detected. Furthermore, the lack of signal can be detected by connecting a retriggerable MMV (Monostable Multi-Vibrator) so as to be triggered by a reproduced synchronizing signal. If the time constant of the MMV is set to slightly longer than the period of the synchronizing signal, then the MMV will be retriggered when the reproduced synchronizing signal is absent. Therefore, the lack of signal can be detected. Furthermore, instead of the display unit, an audible alarm such as a buzzer may be employed.

In the above-described embodiment, recording is accomplished on video tape, but a video disk may be used if desired.

Claims (5)

1. An inter-music detecting method wherein an audio signal in digital form and having an accompanying synchronizing signal is superposed on a video format signal and recorded on a recording medium and reproduced from said recording medium, wherein the improvement comprises, in recording said audio signal, omitting said synchronizing signal from parts thereof corresponding to inter-music intervals of said audio signal, and upon reproducing said audio signal, indicating presence of inter-music intervals by detecting an absence of said synchronizing signal.

2. An inter-music interval detecting system for use in a recording and reproducing system in which an audio signal containing a synchronizing signal is superposed on a video format signal, comprising: for recording said audio signal, muting means for muting said synchronizing signal during inter-music intervals of said audio signal; and for reproducing, means for detecting an absence of said synchronizing signal, and means, operating in response to an output of said detecting means, for producing an indication of presence of inter-music intervals.

3. The inter-music detecting system of claim 2, wherein said muting means comprises a transistor receiving said synchronizing signal on a control input thereof, a capacitor coupled between output electrodes of said transistor, a comparator having a first input terminal coupled to said capacitor for receiving a voltage across said capacitor, and means for applying a reference voltage to a second terminal of said comparator.

4. An inter-music detecting system substan tially as described with reference to the accompanying drawings.

5. An inter-music detecting method substantially as described with reference to the accompanying drawings.