DE3113862A1 - Video recorder for recording a picture carrier which is frequency modulated with the video signal - Google Patents

Abstract

Video recorder recording video signals and sound signals on a common track, for example a helical track, a frequency band being provided for the sound and picture carrier signals between the spectra taken up by the luminance signals and the chrominance signals, and the sound carrier signals being recorded in this band in their original spacings of the transmission standard due to frequency conversion.

Description

Video recorder for recording a with the

Video signal of frequency-modulated video carrier In video recorders is it is known, the video signal by frequency modulation of a picture carrier on so-called To record helical tracks at a predetermined angle (for VHS devices approx. 60) run obliquely in the longitudinal direction of the tape. It is preferably along such a helical track recorded, for example, one field at a time. recording and scanning are done with rotating heads (two heads for VHS), each alternately have contact with the helical tracks. In this way, with relative slow tape speed the high relative speed required for video recording reached between head and tape.

With such devices, the audio signal is on a parallel to the tape edge running longitudinal track with a width of about 1mm with a fixed head recorded and scanned. For recording and scanning of the sound signal is the lower longitudinal speed of the tape and not the Much higher relative speed between head and tape on the helical tracks decisive.

The longitudinal speed of the belt is now in practice to increase the total playing time of a tape is reduced to values on the order of 2 cm / s been.

This low relative speed between the tape and the tape head has an adverse effect on the quality of the recorded audio signal. A hi-fi quality can be practically achieved at this low relative speed can no longer achieve. The recorded audio signal only has a bandwidth from about 70 Hz to max. 10 kHz. Because of the narrow width of the longitudinal track, this results also a relatively poor signal-to-noise ratio. This will be when recording two Sound signals for stereo playback or bilingual playback by the then necessary Halving the width of the longitudinal track even worse.

It is conceivable per se, similar to the audio signal, as is the case with the video disk to be recorded together with the image carrier on the oblique tracks. Such a solution has not yet been successfully implemented in practice.

On the one hand, the available frequency range is already fully utilized. Namely, the range of about O - 1.3> 4 Hz is lowered from that in frequency quadrature modulated color subcarrier and the rest of the frequency range through the frequency spectrum of the modulated image carrier.

A recording of a sound carrier in the narrow one that still exists Sequence gap between the modulated color carrier and the frequency spectrum of the image carrier is also the necessary steep filter flanks for the ink carrier and the Image carrier practically not possible because of the phase and group delay errors that occur. On the other hand, when the audio signal is recorded on the helical tracks, at the playback a considerable disturbance by the head change. When playing back images the head change does not bother, because there is a gap during or shortly before the vertical blanking he follows. When the audio signal is played back, however, this head change is seen as a disturbing one Noise audible because the head change causes the scanning of e.g. one wearer modulated audio signal from the tape is briefly interrupted or phase jumps subject. The resulting needle-shaped interference pulses with a basic frequency of 50 Hz and a large proportion of harmonics generate a continuous background noise. It has been suggested (P31 10 968.3 = H 81/20), the recording of the audio signal on the helical tracks with improved quality and without disturbance by the head change, by the output signals of the two rotating heads are amplified so differently in the audio signal path that the audio signals do not cancel each other out in the overlap area with addition or subtraction can.

This allows recording and reproduction of the audio signals made possible with FM quality, but still remains the result of the well-known sound recording process known disadvantage that the processing of audio signals for recording and playback is associated with a reduction in quality, e.g. susceptibility to noise.

The invention is based on the problem of the quality of the sound recording to improve.

This object is achieved by the invention described in claim 1 solved. Advantageous further developments of the invention are described in the subclaims.

The invention consists essentially in the sound carriers in their distances and modulations prescribed by the standard in this gap in the recording spectrum insert between luminance signal spectrum and chrominance signal spectrum and this Gap at the expense of the upper sideband of the chrominance signal corresponding to this To widen the distances, with the correct position of the sound carrier frequency by difference formation between the standard sound carrier frequency (for CCIR 5.5 or 5.742 MHz) and one Reference frequency, e.g. in PAL the color subcarrier frequency of 4.43> 4Hz obtained will.

A change in the upper sideband of the chrominance signal spectrum results in theoretical errors, but it has been shown that these errors in the reproduced Image are practically imperceptible. The principle of the compensates for PAL receivers Color television system such errors themselves to a far greater extent and for NTSC and SECAM, the bug is not yet big enough to be really annoying.

The advantages of the device according to the invention can be cited: The quality of the original sound broadcast is retained.

An FM sound carrier demodulation for the recording can be dispensed with will.

A compander system can be dispensed with.

There is no need for an automatic level control.

There is no need for two FM modulators for the RF converter.

There is no need to generate a new pilot signal.

The two longitudinal sound recording tracks can be dispensed with.

The tape head can be dispensed with.

In the invention, the high relative speed is the The available bandwidth of the audio signal when recording on the helical tracks is advantageous also used to record the audio signal. Through high-frequency recording of the audio signal and the saving of any demodulation and remodulation Achieve FM quality for the sound. Another advantage is that the previously required longitudinal track for recording the audio signal is omitted can. There can then either be an additional area of magnetic tape there for recording of the image signal can be used or this area can be used additionally. This can either improve the quality of the image recording or reduce tape consumption be reduced. A particularly good utilization of the magnetic tape can be achieved if, according to DE-OS 30 11 635, the previously used synchronous track in parallel to the edge of the tape to mark the inclined tracks and that for head regulation needed to indicate the individual helical tracks with a fixed signal Head derived from the helical tracks using the so-called azimuth angle will. This means that a video recorder can only be used with rotating heads for writing of the helical tracks, i.e. without additional recording heads for longitudinal tracks such as e.g. for the sound recording or the synchronized track. The one that becomes free as a result Tape area enables an increase with the same image quality and the same tape length the playing time by about 16%. That means with one for a playing time of 4 hours provided Cassette an additional playing time of 40 minutes.

The recording of the sound signal in FM allows amplitude fluctuations of the recorded sound carrier largely offset by a limitation can be.

This type of modulation is also one of the basics of: a solution to the task at hand.

The different gain introduced for debugging of the two head output signals is again in the frequency demodulation limited.

An embodiment of the invention is explained with reference to the drawing. FIG. 1 shows the known frequency spectrum for the recording of the individual Signals on the oblique tracks, Fig. 2 the position of the two sound carriers in a modification of the spectrum according to FIG. 1 according to the invention, FIG. 3 shows the effect of the change according to Fig. 2 to the video spectra, Fig. 4 is a block diagram for the recording, FIG. 5 shows a modification of FIG. 4, FIG. 6 shows a block diagram for reproduction, FIG. 7 shows a modification of the circuit shown in FIG. 6, FIG. 8 that of the Heads supplied signal packets, FIG. 9 shows an illustration of an example of a narrow-band FM amplifier in FIGS. 5, 7, and FIG. 10 shows an illustration of an example for a notch filter according to FIGS. 5, 7 and 11, a characteristic curve of the one shown in FIG. 10 Notch-filter combination, Fig. 12 is a schematic representation of the recording apparatus.

In Fig. 1, the frequency range is reduced in the lower frequency range quadrature-modulated color carrier F with a frequency of 0.63> 4Hz and a bandwidth recorded at approx. + 500 kHz. The video signal V is through FM of a picture carrier recorded. Its static modulation characteristic extends between the Frequencies 3.8 and 4.8 MHz, with 3.8> 4Hz being the ultra black level and 4.8> 4Hz corresponds to the white level of the video signal. The modulation results in a frequency spectrum from 1.3 to 7.3 MHz. Due to the head gap, the upper side ligament (above 6 MHz) not completely scanned, so that interference from signal reflections is reduced will. Sound signals are not included in the known spectrum. You will be acquainted with Devices prepared separately and in a track running along the edge of the belt recorded.

In Fig. 2 the two luminance and chrominance signal are spectra shown enlarged, the position of the audio signals introduced by the invention is specified.

Within the frequency spectrum are at the frequencies i, O7 and 1.31 > 4Hz two sound carriers 1 and 2, each modulated with an LF sound signal in FM, are recorded. Namely, if a stereo signal is introduced at the transmitter end that has a distance of FM sound carriers of 250 kHz should be used for the purpose of quality improvement favorable simple implementation also die.Träger 1,2 have a corresponding distance. The two audio signals can be a mono signal, a stereo signal or an audio signal in different languages. The frequencies of the two sound carriers are 1.2 approximately at the maximum 4 of the head-to-tape frequency response characteristic 5, which is used during recording of the entire signal is effective on the helical tracks. There is the slightest disturbance of the image signal given by the audio signal and vice versa, because based on the demodulated video signal, the higher-frequency image components in the selected area only occur for 10% of the transmission time. The one for image sharpness The relevant frequencies, on the other hand, remain unattenuated. At the same time they have Video heads 14 of all home video recorders in the range around 2> 4Hz their greatest sensitivity, so that the point of the optimal signal-to-noise ratio is selected for playback. In order to is the interchangeability of video cassettes with poorly recorded sound carriers problem-free within a cassette system.

Fig. 3 shows in the normal frequency spectrum of the television signal through the invention introduced "bandwidth losses" of the luminance signal and the chrominance signal. The chrominance signal penalty at C is 0.06 MHz. The loss of the luminance signal is 0.10 MHz. The loss of resolution of the luminance signal is negligible and the single sideband error of the chrominance signal is not noticeable.

In Fig. 4, the composite signal in the circuit 6 is frequency-selective Means in the modulated color carrier F and the luminance signal Y (luminance signal) separated.

The modulated PAL color carrier F (chrominance signal) is in the frequency converter 7 converted from its original frequency 4.43> 4Hz to the frequency 0.63> 4Hz and a notch filter N, which is a filter with an extremely steep slope for shifting the upper edge of the chrominance band, the adder 8 is supplied. The luminance signal Y is modulated onto an image carrier in the frequency modulator 9, creating a frequency spectrum from 1.3 to 7.3> 4 Hz according to FIG. 1. In this frequency spectrum, in the circuit 10 by a notch filter, not shown, the lower edge of the Luminance band up postponed. The remaining signal is also fed to adder 8. Two audio signals NF1 and NF2, e.g. from a microphone input are in two frequency modulators 11,12 with two carriers the frequency of 1.07 and 1.31> 4Hz, which is also modulated to the adder 8 are fed. In the case of an LF frequency band of 15 kHz to be transmitted, a FM hub of + 50 kHz selected, resulting in modulation bandwidths of 1.07 and 1.31 > 4Hz + 70 kHz result. To avoid interference in the Y signal from the two Sound carriers are in the circuit 10, the frequencies of the two sound carriers according to Fig. 2 suppressed by the aforementioned notch filter. The output of the adder 8 contains the signals shown in Fig. 2 and is applied to the magnetic heads 14a, 14b alternately fed for recording on a magnetic tape. This in Fig. 1 or The composite signal shown in FIG. 2 is then recorded on the helical tracks of a magnetic tape. For recording audio signals such as those broadcast by television stations and by a tuner T are received, mixers or modulators Ml and M2 are provided, which the received and converted to intermediate frequency ZFl: (5.5 MHz) and ZF2 (5.742 MHz) modulated sound carrier 1.2 while maintaining the high frequency on frequencies of Convert 1.07 and 1.31> 4Hz.

A crystal stabilized reference frequency source is used for this purpose R with a frequency of 4.43> 4Hz is provided, which is already the case with PAL devices existing color carrier can be the reference oscillator. The IC MM 1496 (Motorola) has been tried and tested. The output terminals of the mixers Ml and M2 are connected via switches S1 and S2 less adder, so that the device can be used can be switched to LF audio signal and HF audio signal. The source R can also be a separate one Be an oscillator.

FIG. 5 shows a modification of FIG. 4. The difference consists in the use of a single notch filter N for chrominance and luminance channels, which is shown in Fig. 10 in detail. For this purpose, the output signals of the Frequency converter 7 and the filter circuit 10 is fed to an adder 8, the In contrast to FIG. 4, the audio signals are not supplied. The output of the adder 8 is fed to the notch filter N and passes from there to a further adder stage 8a, to which the audio signals from switches S1 and S2 are also fed.

Fig. 6 shows a circuit for reproducing the recorded spectrum according to FIG. 2. The signal alternately sampled by the heads 14a, 14b is shown in FIG an amplifier 15 amplified and with separate notch filters Ni and N2 in the The chrominance channel and the luminance channel are split.

Demodulators 18 and 20 demodulate these signals and route them demodulated signals to an adder circuit in which the composite signal is recovered will. Further processing takes place in the usual, known manner. In front of the entrances the notch filter N1, N2, the audio signal is split off and two via filters 21,22 Mixers M1, M2 supplied, which by means of the reference frequency of the source R, the audio IF signals Recover TonZF1, TonZF2. These IF signals can be implemented directly or via re-implementation into the reception channels of the VHF / UHF band are fed to the receiver. The scanned Audio signals can also be demodulated directly if this is required in the recorder will.

In Fig. 7 that is alternately scanned by the heads 14a, 14b Signal mixture according to FIG. 1 amplified in the amplifiers 15a and 15b and via the Notch filter N from Sound signal freed and through filters 16,17 in the split the modulated color carrier F and the modulated image carrier YFM. Since the Change between & n heads 14a, 14b during the duration of the vertical blanking interval takes place, no additional measures are required with regard to the video signals, except for a hard electronic switch 27 for the head signals of the amplifier outputs 15a and 15b for perfect color conversion and V-FM demodulation. The color carrier F is converted back to the frequency of 4.43> 4 Hz in the frequency converter 18 and fed to the adder 19. In the frequency demodulator 20, the luminance signal Y obtained and fed to the adder 19.

The total composite signal supplied by the heads 14a and 14b has Overlapping zones in which both heads 14a, 14b are in contact with the tape and output signals deliver.

These overlap zones virtually form one for the sound carrier signals soft electronic fader.

8 shows the composite signal supplied by the heads 14a and 14b, where the switching points for Y and color are marked. Because these areas of overlap The signal parts in these zones can be subject to phase fluctuations increase or delete the addition, since both carrier packets because of the transmitted Color carrier information with reduced carrier in AM carefully for equal amplitude are set. This cancellation produces sound disturbances.

Before any circuit to linearize the envelope of the Heads supplied composite video signal or in front of any device for hard electronic cross-fading is the entire signal mixture supplied by the heads 14a, 14b branched off. The two modulated sound carriers be with-narrowband Filters 21, 22 selectively separated from the composite signal according to FIG. 2 and mixers Ml, M2 supplied. The mixers deliver the two audio signals TonZF1 and TonZF2. That from the head 14a or from the amplifier 15a delivered total signal is before the supply fed to the demodulators 23, 24 of an adder 25. The head 14b or The total signal supplied by the amplifier 15b is fed to an amplifier 26, whose Output signal is also fed to the adder 25. The output signal of the In any case, the adder stage also has on during the switching phase of the heads Signal with audio signal, so that the otherwise unavoidable 50 Hz interference does not occur can occur.

FIG. 9 shows an example that is used as a filter 21, 22 and at the same time as an amplifier is suitable for the FM sound IF signals. Such a component can be used e.g. of the RCA broadband amplifier IC "s CA 3011 can be realized.

For the notch filter N, an exemplary embodiment was created in practice Tried in which the notch filter N out of four in the standard color television receiver types used for the suppression of the color carrier in the Y-channel has been, i.e. has been modified for the other frequency and bandwidth. One such The filter is shown in FIG.

FIG. 11 shows a characteristic curve of the filter according to FIG. 10, the Filters are sized so that their highest cutoff points are at the band limits.

Fig. 12 shows a schematic construction of the head wheel with a Band 28, which encloses a head wheel drum 30 with two heads 14a, 14b in the n -type, with skewed tracks 29 being written on the tape 28. Line 35 shows that the two heads 14a, 14b can simultaneously scan in the areas 36,37.

In the above description, frequencies for Sound carrier and reference carrier specified. In practice, depending on the type of application both the exact values specified in the standard and simplified values (e.g. 5.7421875 MHz or only 5.74> 4Hz for the audio signal NF2) can be used a tried and tested embodiment of a PAL device (Fig. 8) was used as the reference carrier source R a crystal stabilized PAL reference oscillator with a frequency of 4.433618 > 4Hz + 1 kHz is used, but the accuracy may be lower in most cases must be set as it is necessary for the decoding of the PAL signals. the The accuracy must be so great that the demodulation is in the linear range of the demodulator characteristic he follows.

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Claims (11)

Claims video recorder1 its video signal recording spectrum which contains audio signals as a modulation of one or more carrier (s), characterized in, that between the luminance signal spectrum and the chrominance signal spectrum arranged below it a range is provided for the frequency or frequencies assigned to the audio signal, that the area is so large that he or the sound carrier and possibly one Pilot carrier with the corresponding distances of the broadcasting standard can accommodate that the chrominance signal channel and the luminance signal channel filter with steep-walled Characteristics are assigned to the frequency range between the band limits of the two spectra to at least the range required for the sound carrier (s) define, and that a stabilized reference frequency voltage source (R) is provided is whose reference frequency is dimensioned so that the modulated sound carrier or carriers (1,2) by forming the difference with the reference frequency in the original distance in the Frequency range between luminance and chrominance spectrum or by adding up from this area can be converted to the original location. 2. Video recorder according to claim 1 for PAL color television signals, characterized characterized in that the reference signal source (R) is based on the PAL color subcarrier frequency tuned reference oscillator is. 3. Video recorder according to claim 1 or 2, characterized in that the source (R) is quartz stabilized. 4. Video recorder according to claim 1 for SECAM color television signals, characterized characterized in that the reference signal source is a stabilized resonant circuit. 5. Video recorder according to claim 4, characterized in that the Oscillating circuit a quartz stabilized, tuned to the PAL frequency Standard G Circle is (4.43618 MHz). 6. Video recorder according to claim 1 for NTSC color television signals, characterized characterized in that the reference signal source is a crystal stabilized oscillator is. 7. Video recorder according to one of claims 1 - 6, characterized in that that a mixer (M1, M2) is provided for recording at its input or at its inputs the high-frequency, modulated sound carriers in IF range (with PAL 5.5 MHz, 5.75 MHz) and the reference frequency (for PAL 4.43 MHz) and their output signals are two modulated sound carriers suitable for direct recording the difference frequency between the reference frequency and the sound carrier (1.07 MHz, 1.31 MHz), and that for reproduction of the mixer (M1, M2) is switched so that the scanned Sound carrier and the reference frequency are added and so the sound carrier in the original IF position (5.5 MHz, 5.75 MHz). 8. Video recorder according to claim 7, characterized in that the Sound carrier for playback on the antenna modulator at the output of the video recorder are fed. 9. Video recorder according to one of claims 1 - 8, characterized in that that when using a pilot carrier to define the type of sound carrier modulation (Mono, stereo, bilingual) for recording the difference frequencies and for the reproduction the sum frequencies of the reference frequency and the original or sampled Pilot carriers are formed. 10. Video recorder according to one of claims 1 - 9, characterized in that that the chrominance signal channel and the luminance channel are assigned a common filter (N) which contains the series connection of several, preferably four, notch filters, where the zeros of two filters lie at the points of the band limits. 11. Video recorder according to one of claims 1 - 9, characterized in that that the luminance signal channel and the chrominance channel are each assigned a filter (N) is.