DE3314782A1 - Video recorder recording a PAL colour subcarrier - Google Patents

Abstract

In a video recorder, the colour subcarrier (Fm), the frequency of which is reduced, is interleaved into the lower frequency band of the luminance signal (Y) whilst retaining the PAL quarter-line offset, and recorded together with this luminance signal by frequency modulation of the picture carrier. As a result, the frequency band below the modulated picture carrier becomes free for recording audio signals. <IMAGE>

Description

Video recorder with recording of a PAL color carrier

With video recorders according to the systems VHS, Betamax and V 2000 the luminance signal through frequency modulation of an image carrier with two video heads alternately recorded on oblique tracks of a magnetic tape. Below the frequency range of the modulated image carrier is reduced in frequency to about 0.63 MHz Ink carrier recorded. It is also known to improve the sound quality (DE-OS 31 16 130), one or more frequency-modulated with audio signals with the video heads Record sound carriers. Since the available recording bandwidth of about 6 NHz is occupied by the color carrier and the image carrier, must for such Sound carrier an additional frequency range can be created. It is known in the frequency range of the modulated video carrier, frequency ranges for the sound carrier to suppress or the upper sideband of the ink carrier or the lower sideband of the image carrier. Such measures can lead to quality reductions the image reproduction.

The invention is based on the object of better utilization to create the available recording bandwidth, in particular without impairment record additional signals such as multiple audio signals for the image quality can.

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

In the solution according to the invention, the color carrier is thus included in the luminance signal moved into it, and the resulting combined signal by frequency modulation recorded on the image carrier. The one occupied by the modulated image carrier is thereby used Frequency range not increased. The frequency range previously occupied by the color carrier from about 0.13 to 1.0 MHz, however, it enables the recording of other signals free. In this frequency range, for example, a high-quality audio signal can then be recorded be, in particular several sound carriers frequency-modulated with sound signals or a PCM beep. A sound signal recorded in this way has, in terms of bandwidth, Signal-to-noise ratio and pitch fluctuations are much higher quality than a sound signal, recorded in a known manner as an LF signal on a longitudinal track of the magnetic tape will. The invention applies to all three video recording systems mentioned at the outset applicable. The separation of the luminance signal necessary for recording and playback and color carrier is in a simple manner with comb filters known for this purpose possible. Because during playback there is a coupling of the color subcarrier frequency with the luminance signal remains is a mixture of the reproduced signal with studio signals possible. Well-known video recorders according to the VHS or Betamax system have at the Reproduction no coupling of the color subcarrier frequency with the line frequency. the The invention is generally applicable to the recording of a color television signal, i. especially with video recorders Magnetic tape and optical disc players. Another advantage is that errors caused by playback Fluctuations in the relative speed between the video heads and the magnetic tape fall out when converting the frequencies of color and sound carriers, because the modulated carrier and the mixed carrier coupled to the line frequency are subject to the same timing errors.

Preferably, the frequency-reduced color subcarrier is in front its nesting in the luminance signal regardless of the respective color saturation always regulated to the full signal peak value of e.g. 0.7 V peak-to-peak. then is the amplitude of the representing the color saturation in the recording Color carrier falsified. During playback, the burst and the Synchronizing pulses compared in amplitude. With a manipulated variable obtained from it the amplitude of the color carrier is again s that corresponding to the color saturation correct size controlled back. In this way, the available dynamic range are always fully utilized regardless of the respective color carrier amplitude, so that there is an improved signal-to-noise ratio in the color signal during playback.

This control of the color carrier amplitude takes place for one line at a time with a constant control voltage, because changes in color saturation in the course one line may not be corrected. Then it would be for the playback Back control of the color subcarrier amplitude, no identification signal available. For example is the amplitude of the color sync signal at the beginning of each line during playback compared with the amplitude of the line sync pulses. This creates a control voltage obtained, each of the amplitude of the color sync signal to that of the standard Value controls and remains constant during the following line. This control voltage then inevitably controls the amplitude of the color carrier during this line again to the correct value corresponding to the respective color saturation.

During the recording, the control is carried out, for example, so that in every line the maximum color subcarrier amplitude corresponds to the signal peak value determined by the modulation range of e.g. 0.7 V. Then also with a low mean color subcarrier amplitude and color saturation is the total amplitude range available for the color carrier fully utilized.

Since the recording of the color information no longer takes place with an in the Frequency reduced color subcarrier below the frequency range of the modulated Image carrier takes place, the previously required band limitation of the lower sideband can of the image carrier are omitted. A previously required high-pass filter is then used for recording no longer required for the image carrier with a cut-off frequency of e.g. 1.1 MHz. This also has the advantage that frequency components also lie below 1 MHz of the modulated image carrier and thereby the image sharpness in Line direction and the signal-to-noise ratio in image reproduction can be increased.

When using transversal filters for recording and for For playback it is beneficial to regenerate the lost vertical resolution otherwise the image sharpness in the vertical direction will be poorer during playback can be. For this purpose, so-called circuits for vertical aperture correction are known, in which signals from consecutive lines are combined. Since the signal components for vertical image details are small, can also with the aforementioned regeneration Noise components are added. For this reason, it is advantageous in the inventive Recording during playback a circuit to increase the vertical details with a frequency increase of 200-500 KHz.

The reduction in image sharpness in the vertical direction is due to the Comb filter used to separate color carrier and luminance signal conditionally, in which signals from successive lines are added.

The invention is based on the drawing of several exemplary embodiments explained. 1 shows frequency spectra for the recording according to the invention, FIG. 2 shows a block diagram for the recording, FIG. 3 shows a block diagram for the Playback with a recording according to FIG. 2, FIG. 4 shows a block diagram for the recording with a different type of sound recording and FIG. 5 is a block diagram for the Playback with a recording according to FIG. 4.

1a shows the luminance signal Y with a bandwidth of 3 MHz. In the lower frequency range from 0.13 to 1.13 MIIz is in the frequency modified color carrier Fm reduced to 0.63 NHz inserted. Implementation of the Frequency of the color subcarrier from 4.43 MHz to 0.63 NHz takes place so that the quarter line offset is retained in the color subcarrier frequency (according to DE-PS 11 79 986). As a result, the Spectral lines of the luminance signal Y and the color carrier Fm nested in one another.

The signal according to FIG. 1a is modulated onto the picture carrier in Fm.

Fig. 1b shows the resulting signal. The image carrier B has for the black level a frequency of 4.1 MHz and the horizontally hatched frequency deviation from 3.8 MHz for the synchronous floor to 4.8 MHz for the white value. The color carrier Fm occupies the frequency range of 2.97 -3.97 N} iz shown diagonally hatched. At the frequencies of 1.92 and 2.16MHz, two are frequency-modulated with sound signals Sound carriers T1m and T2m recorded. These frequency ranges are in the frequency domain of the image carrier B cut out with appropriate filters. Since the color carrier Fm within of the frequency range of the image carrier B, the frequency range is from 0 - approx. 1.1 MHz free.

According to FIG. 1c, a is in the free frequency range up to about i, 1 NHz PCM audio signal recorded according to the principle of the so-called Biphase PC! 1. The bandwidth of 1 MHz enables a High quality PCM sound recording.

In Fig. Id there are four in the free frequency range of 0-1.1 NIiz Sound carriers Tlm ', T2m', Tlm, T2m frequency-modulated with sound signals in the illustrated Frequencies recorded. The meaning of these four sound carriers is illustrated in Fig. 2 explained.

Fig. Le shows this in the reproduction by FN femodulation and frequency conversion obtained signal. This consists of the luminance signal Y with a bandwidth of 3 MHz, the color carrier F converted back to the frequency of 4.43 MHz and the two sound carriers T1, T2 with the standardized frequencies of 5.5 and 5.74 MHz for one Stereo sound transmission or a transmission in two different languages.

FIG. 2 shows a recording circuit for a recording according to FIG. 1d. The tuner 2 fed by the antenna 1 with a television broadcast signal delivers the standardized composite signal and the sound carriers T1, T2. With the comb filter 3 this becomes FBAS signal split into the modulated color carrier F and the luminance signal Y. Such comb filters for separating the luminance signal and color carrier with one another nested frequency spectra are known and described in more detail in "Telefunken-Zeitung" 1964, issue 2, pages 127-130. The color carrier.F reaches 4.43 NHz + 0.5 via the MHz matched bandpass filter 4 to mixer stage 5.

With the synchronous separation stage 6, the synchronous pulses S are from the luminance signal Y separated and fed to the phase comparison stage 7, which is part of a PLL control circuit with the oscillator 8 and the frequency divider 9 is. The oscillator 8 swings up a frequency of 5.07031250> 1Hz = 324.5 fIt, where fH is the line frequency. The mixer carrier generated in the oscillator 8 with this frequency becomes the mixer stage 5 supplied. At the output of the mixer 5, the reduced frequency appears Color carrier Fm with the frequency. Of 0.63669375 MHz, which via the low-pass filter 10 with a Cutoff frequency of 1.15> 1Hz of the adder 11 is fed. The luminance signal Y arrives through the amplifier 12, the low-pass filter 13 with a Grenzfreqenz of 3 Niiz and the delay element 111 serving to compensate for the delay also appear the adder 11. At the output of the adder 11 is the signal Fm BAS according to Fig. La. This signal reaches the FM modulator via the pre-emphasis stage 15 16, which generates the signal according to FIG. 1d without the sound carrier.

This signal passes through the high-pass filter 17 with a cutoff frequency from 1.1 z to the adder stage 18.

The sync pulses S are also fed to the circuit 19, those for generating the mixed carriers for converting the frequencies of the sound carriers Ti, T2 is used by the tuner 2 via the bandpass filter 20 with a passage width of 5.62 MHz + 200 KHz are fed to the mixer 21. Circuit 19 includes two PLL circuits 1 each with a phase comparison stage, a frequency divider and a Oscillator included. The frequency dividers each divide the oscillator frequency down to the line frequency ff1. The oscillator 22 creates a mixing carrier with the frequency of 4.75> 1Hz = 304.fH and the oscillator 23 a mixed carrier with the frequency of 5.25> 1Hz = 336 * fH.

The frequency dividers shown thus have the division factors 304 or 336. With the changeover switch 24, which is operated by the servo circuit 25 with the 25 Hz switching voltage 26 is switched from field to field, are alternated from field to field the two mixing carriers are fed to the mixer 21 at these frequencies. The mixer stage 21 thus delivers two different frequencies from one field to another converted sound carriers with the following values: Field 1: Tlm with 5.5 - 4.75 = 0.75 MiIz and T2m = 5.7421875 - 4.75 = 0.9921875 MHz.

Field 2: Tim 'with 5.5 - 5.25 = 0.25> 1Hz and T2m' with 5.7'121875 - 5.25 = 0.4921875 MHz.

These are reduced in frequency and from half-picture to half-picture Switched sound carriers pass through the low-pass filter 27 with a cut-off frequency of 1.1> 1Hz to the adder 18. The output of the adder 18 is thus the Signal according to Fig.

ld, which is fed through the amplifier 28 to the video heads 29 and with this is recorded on the magnetic tape 30.

2a shows a modification of the circuit 19. The two oscillators 22, 23 are replaced by a single oscillator 31. Switching the from the oscillator 31 generated frequency is done by switching the division factor n of the frequency divider by the switching voltage i6 between n = 304 and n = 336.

The described switching of the frequencies of the sound carriers Ti, T2 has following purpose. In the case of the frequency position indicated in FIG. 1d, the sound carriers are the so-called azimuth losses, the crosstalk attenuation between neighboring Cause oblique tracks, no longer effective. It would therefore be recorded for that Sound carrier, crosstalk can occur between adjacent tracks. When the frequency of the sound carrier is switched from field to field, the sound carriers in two adjacent helical tracks have different frequencies when playing can be separated from each other with filters.

This means that there is crosstalk between the sound carriers of adjacent ones Avoided helical marks. This solution is described in more detail in the older application P 33 o6 978.6.

In Fig. 2, the oscillator 8 oscillates above the frequency of the color carrier F. If the oscillator 8 is to oscillate below the frequency of the color carrier F, a mixing frequency of 3.79687500> 1Hz = 243.flI is preferred when recording chosen so that a frequency of 0.63674375> 1Hz for the color carrier Fm results. This mixed carrier is used for playback at the same frequency again a frequency increase to 4.4361875> 1Hz. The recording of the phonograms T takes place with about 10-20% of the recording current of the image carrier B, um disturbing To avoid interference during playback.

In Fig. 3, the signal according to Fig. Led with that by the switching voltage 26 actuated switch 32 and the video heads 29 from field to field of the oblique tracks of the magnetic tape 30 are scanned. This signal gets over the limiter 33 to the FM demodulator 34, which generates the signal according to FIG. 1a. This signal passes through the low-pass filter 35 with a cut-off frequency of 3> 1 Hz and the de-emphasis stage 36 and the amplifier 37 to the inputs of the two comb filters 38.39.

The comb filters 38, 39 are designed so that they nested Separate the frequency spectra of the luminance signal Y and the color carrier F from one another. The comb filter 38 supplies the luminance signal Y via the transit time compensation serving delay element 40 to the adder 41. The comb filter 39 supplies the Color carrier Fm of 0.63 MHz, which passes through the low-pass filter 42 with a cutoff frequency of 1.1> 1Hz of the mixer 43 is fed. From the amplifier 37 are with the sync pulse separation stage 44 also the sync pulses S derivatized and for synchronizing the PLL circuit 45 with the oscillator 46, which corresponds to the circuit 19 in FIG is working. The oscillator 26 generates a mixed carrier with the frequency of 5.07 > 1Hz = 324.5cfH. The mixing stage 43 thereby supplies the color carrier again at the output F with the PAL color subcarrier frequency of 4.43361875 MHz, which is via the bandpass filter 47 with A pass band of 4.43 + 0.5> 1 Hz reaches the adder 41. At The FBAS signal corresponding to the standard is thus available to terminal 48.

The synchronization signal S also synchronizes the PLL circuit 49. Its oscillator 50 generates two mixing carriers alternately from field to field -with the frequencies of 4.75 and 5.25 MHz, which reach the mixer 51. to for this purpose the division factor n of the frequency divider of the PLL circuit 9 is determined by the 25 Hz switching voltage 26 from field to field between the values n = 304 and n = 336 switched. At the output of the mixer 51 then arise again both sound carriers T1, T2 with the standardized frequencies of 5.5 and 5.7421875 MHz, which over the band pass 52rrit a pass band of 5.62 + 0.2 MHz, the amplifier 53, the limiter 54 and the amplifier 55 of the output terminal 56 are fed. The signals at terminals 48, 56 thus form the complete one again TV signal with picture and sound information.

The switching voltage 26 is converted into a while with the pulse shaper 57 of the head change generated pulse 58 which increases the gain of the amplifier 53 increased for a short time. This can reduce disruptions caused by changing heads will. The pulse 58 can act in the sense that it during the head change causes the amplifier 23 to self-oscillate at its resonance frequency, so that even in the event of a failure of the sound carriers T1, T2 at the output of the bandpass filter 52 Sound carriers are generated. This solution is described in more detail in DE-OS 31 16 130

Fig. 4 shows a recording circuit for the type of recording according to Fig. Lb. The color carrier F becomes similar with the Mæhstufe 59 and the oscillator 60 as in Fig. 2 to a color carrier Fm with the reduced frequency of 0c63> 1Hz implemented and added to the luminance signal Y in the adder 61. The combined Signal passes to the FM modulator 62 and from there to the filter 63, which in the Frequencies 1.92 and 2.16> 1Hz has blocking points. The sound carrier T1 with 5.5 > 1Hz and T2 with 5,7421875> 1Hz are made by the mixer 64 and the oscillator 65 converted to sound carrier Tlm with 1.92 and T2m with 2.16> 1Hz.

These sound carriers become the one coming from the filter 63 in the adder 66 Signal added. The output signal of the adder 66 according to FIG. 1b is with recorded on the magnetic tape 30 by the video heads 29. In this embodiment So are the sound carriers within the frequency range of the image carrier B, while the frequency range below from about 0 to 1.1> 1Hz is free for other signals remain.

Fig. 5 shows the corresponding reproduction circuit. The one with the video pots 29 signal sampled from the magnetic tape 30 according to FIG. 1b reaches the filter 63, which corresponds to the filter 63 in Fig. 4. With the filter 63, the sound carriers Tlm and T2m suppressed. The FM demodulator 67 supplies the signal according to FIG. La. This is converted with the comb filters 68,69 into the luminance signal Y and the color carrier Fm split up. The color carrier Fm is made with the oscillator 70 and the mixer 71 converted back to the original frequency of 4.43> 1Hz and the adder 72 supplied. This again supplies the standardized composite signal at terminal 73.

The two sound carriers Tim and T2m are set to 1.92 and 2.1> 1Hz tuned bandpass filters 74,75 selectively evaluated and fed to the adder 76. The frequencies of these two sound carriers are set by the oscillator 77 and the mixer 78 as in Fig. 3 converted back to the original frequencies of 5.5 and 5.742 MHz, so that the standardized sound carriers T1, T2 are again at terminal 79. The signals at the terminals 73,79 thus again form the standardized television broadcast signal for the image information and the sound information. The switching of the audio carrier frequencies 2 is not necessary here because in the frequency range of 2> 1Hz the Azimuth losses are sufficiently effective for crosstalk attenuation.

The oscillator 8 in FIG. 2 and the oscillator 46 in FIG. 3 oscillate at the same frequency and are coupled to the line frequency in the same way, because the frequency reduction of the color carrier when recording and the conversion back be done with the same mixed carrier frequency during playback. Therefore, at the same levels are used for recording and playback, i.e. the stages 5,7,8,9 in FIG. 2 can have the function of the stages 43,35,46 during playback in Fig. 3 meet. The same applies to the corresponding implementation of the frequencies the sound carrier T1, T2 because the frequency conversion of the color carrier and the sound carrier done in the same way.

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Claims (16)

P a t e n t a n t a n s p r ü c h e Video recorder with recording of a PAL color carrier (F) and an image carrier frequency-modulated with the luminance signal (B) characterized by the following features: a) The frequency of the color carrier (F) is maintained at the PAL quarter offset to a frequency (0.63 MHz) in the lower Frequency range of the luminance signal (Y) converted and the luminance signal (Y) added (Fig. Ia). b) The combination of the luminance signal (Y) and the color carrier (Fm) is modulated onto the image carrier (B) in FM and recorded in this form. 2. Recorder according to claim 1, characterized in that the Reproduce the frequency of the color carrier (Fm) back to that of the standard The value is downsized (Fig. 3.5). 3. Recorder according to claim 1 or 2, characterized in that the Implementation of the frequency of the color carrier (Fm) takes place with a mixed carrier whose Frequency in full-line offset or in half-line offset coupled with the line frequency is. 4. Recorder according to claim 1 - 3, characterized in that the mixing carrier during recording and playback of the same, coupled with the line frequency Oscillator (8,46) is derived. 5. Recorder according to claim 1, characterized in that the Recording and / or the luminance signal (Y) and the color carrier during playback (Fm) can be separated from one another with comb filters (3.38, 39.68.69) (Fig. 2,3,5). 6. Recorder according to claim 1, characterized in that below recorded a sound signal of the frequency range occupied by the image carrier (B) will. 7. Recorder according to claim 6, characterized in that the audio signal is recorded by FM of a phonogram (T). 8. Recorder according to claim 7, characterized in that the frequency of the sound carrier (T> - from field to field between two different values is switched. 9. Recorder according to claim 1, characterized in that-the audio signal is a PCM signal. (Fig. Ic). 10. Recorder according to claim 7, characterized in that the Record the frequency of the sound carrier (T) with a mixed carrier on a lower one Value implemented and when played back with the same mixed carrier back to the Value corresponding to the standard is converted back. 11. Recorder according to claim 10, characterized in that the Reduction of the frequency of the sound carrier (T) of the full line offset present in the standard or half-line offset is preserved by using the frequency of the mixing carrier the line frequency (fH) is coupled. 12. Recorder according to claim 7, characterized in that the amplitude of the sound carrier (T) is about 10-20% of the amplitude of the image carrier (B). 13. Recorder according to claim 1, characterized in that the Recording and / or a circuit during playback in the path of the luminance signal (Y) to increase the sharpness of the image in the horizontal direction. 14. Recorder according to claim 1, characterized in that the Playback provided a circuit to increase the sharpness of the image in the vertical direction is. 15. Recorder according to claim 1, characterized in that the Record the amplitude of the frequency-reduced color carrier (Fm) including Color burst before being added to the luminance (Y) signal on each line to an approximately constant maximum value that is independent of the mean color saturation is controlled. 16. Recorder according to claim 15, characterized in that the Playback by comparing the amplitude of the color sync signal and the sync pulses a control voltage gained and thus the amplitude of the color carrier in each line (Fm) is controlled back to the value corresponding to the respective color saturation will.