DEVICES FOR MULTI-STANDARD RECORDING ON A VIDEO TAPE

Abstract: A device for recording video on a tape, like for instance a Video Cassette Recorder (VCR), uses a drum (2) with at least two video heads (12) and at least two audio heads (10) according to the video standards providing hi-fi sound (VHS hi-fi). The device can perform NTSC, PAL and SECAM hi-fi recording thanks to a PAL/SECAM-type drum (2). Relative heights between heads (10, 12) are unchanged compared to a PAL/SECAM-type drum (2) used for conventional PAL/SECAM recording.

Description: Devices for multi-standard recording on a video tape The invention relates to devices for recording on a video tape, notably Video Cassette Recorders (VCRs). Today the VHS-Standard provides two independent standards for video recording, that is PAL/SECAM and NTSC, for Europe and USA respectively. Both standards need a dedicated drum in order to accomplish the different speed of drum and tape transport for best picture and hi-fi performance. In hi-fi - VCRs, regardless of the standard, all are equipped with 6 heads : two pairs of double azimuth video heads for SP (Standard Play) and LP (Long Play) as well as two hi- fi audio heads. The most significant difference between a PAL/SECAM hi-fi VCR and a NTSC hi-fi one is the angle of the location between video heads and audio heads as far as the drum is concerned. For PAL/SECAM this angle is 240deg and 1 20deg for NTSC. Furthermore the relative heights and the track width of the heads play a part. It is known there are drums in the market, which can record according to both hi-fi standards, PAL and NTSC. Such kind of drum, mostly used in Asia, have again a different head composition, that is 1 20deg (like NTSC-type drum) with compromised relative heights and track width to fulfil the requirements for better NTSC hi-fi and PAL hi-fi compatibility, but the side effect is a quite poor trick mode performance in NTSC. However, due to the harsh LP head track width requirement in SECAM, this kind of drum was not able to provide acceptable trick modes in SECAM and PAL. The goal of the invention is to provide a VCR with a drum which can record according to both hi-fi standards (PAL/SECAM hi-fi, NTSC hi-fi), with acceptable trick modes. The invention proposes a device for recording on a video tape comprising a drum carrying at least two video heads and at least two audio heads and able to perform notably NTSC-hi-fi-Recording, characterised in that said drum is of the PAL/SECAM-type. In this drum, each audio head is situated at an angle of 60deg in the rotation direction with reference to the video heads. The use of a PAL/SECAM-type drum for NTSC-hi-fi-recording has given good results, even in trick modes. The tape can then be read by a NTSC set using a NTSC-type-drum with acceptable image quality. Moreover, there is no need for compromise in relative heights : a PAL/SECAM-type drum optimised for PAL/SECAM can be used to record NTSC- hi-fi on a video tape. As previously mentioned, the results are good for NTSC tapes, and of course the results with PAL/SECAM tapes are excellent. The device of the invention is therefore able to perform NTSC, PAL and SECAM hi-fi recording. The invention will be explained below in relation with the attached drawings, wherein : - figure 1 is a sketch representing the main elements of a device for recording on a video tape ; - figure 2 is a top view of a PAL/SECAM-type drum ; - figure 3 is a top view a NTSC-type drum. A device for recording on a video tape 1 , e.g. a VCR, conventionally comprises a cylindrical rotating drum 2 around which the tape 1 is wrapped at least on half the circumference of the drum 2. The drum 2 rotates around its axis in anti-clockwise direction R as seen from the top. As conventional, the video signal read on the tape or write on the tape is sent to or comes from a video processor 4. Thanks to a synchronisation separator 6 which extracts the synchronisation pulses from the video composite signal, an upcontrolier 8 is fed with a synchronisation signal in order to control the rotation of the drum 2 and the use of various magnetic heads via a flip/flop signal FF. The rotating drum 2 carries at least a pair of magnetic heads 1 2 for recording and playing video on the magnetic tape 1 . Two pairs of video heads can be provided in order to achieve playing and recording with two different speeds of the tape, leading thus to Long Play (LP, slow motion of the tape, little width heads) and Standard Play (SP, normal motion of the tape, mean width heads). In hi-fi video, the drum 2 is provided with a pair of audio heads 10, which read or record an audio signal on the same part of the tape, but at a different depth with a different azimuth. The audio heads 10 are situated on the edge of the drum at a point defining a specific angle relatively to the video heads 1 2. The specific angle is measured along the edge 20 of the drum 2 around the drum axis. In NTSC-type-drums, each audio head 10 contacts a track 1 20deg before the following video head 12 whereas in PAL/SECAM-type-drums (sometimes called European drums) each audio head 10 contacts a track 60deg before the following video head 1 2. Said in a different way, the audio heads 10 are situated at 1 20deg (β) and 300deg with respect to the video head 1 2 along the edge 20 of the drum 2 in the rotation direction R in NTSC-type-drum (figure 3) ; the audio heads 10 are situated at 60deg (α) and 240deg from the video head 1 2 along the edge 20 of the drum 2 in the rotation direction R in PAL/SECAM-type-drum (figure 2) . As a consequence, PAL/SECAM-type-drum are frequently referred to as 240deg-drum and NTSC-type-drum as 1 20deg-drum. In each standard, as the video and audio heads 1 2, 10 are not at the same position, they are not reading or recording the tape 1 at the same moment : the tape moves between audio reading/recording and video reading/recording. For instance, the delay corresponding to 1 20deg on a NTSC-type-drum playing or recording in NTSC standard is 5.55 ms. In PAL, the delay corresponding to 240deg of the PAL/SECAM-type-drum is 13.33 ms. In order to nevertheless read/write audio and video on the same track, the audio and video heads 10, 1 2 are not situated at the same level on the drum 2, axially speaking. The axial distance between audio heads 10 and video heads 1 2 is called relative height and its optimum value varies according to the standard. The PAL/SECAM-type-drums and the NTSC-type-drums are thus realised with different relative heights. According to the teachings of the invention, the VCR uses a PAL/SECAM-type-drum (as shown in figure 2), optimised for PAL/SECAM (as in a conventional PAL/SECAM VCR), for NTSC hi-fi playing and recording. As previously mentioned, the fact that the drum is optimised for PAL/SECAM means that the relative height of audio heads 10 with reference to video heads 12 is computed to match best the standardised rotation speed of the drum 2, the speed of the tape 1 and angle between heads (240deg for PAL/SECAM-type- drum). in a PAL/SECAM-type-drum optimised for PAL/SECAM, as in the invention, the relative height between an audio head and a standard-play head is between 70 μm and 74 μm. As the NTSC standard works at 60 Hz (instead of 50 Hz for PAL/SECAM), when playing or recording NTSC with the PAL/SECAM-type-drum, the delay between the audio head 10 and the video head 1 2 corresponding to 240deg on the drum 2 is equal to 1 1 .1 1 ms. Due to the difference in video and hi-fi audio head and relative height and angle between a NTSC-type-drum and a PAL/SECAM-type-drum, the optimum tracking position for hi-fi and video differs. Hence some compromise has to take into account for the NTSC hi-fi SP interchangeability, unlike between NTSC-type-Drum and PAL/SECAM-type-Drum (1 20deg, optimised for PAL and NTSC). The SLP (LP in NTSC) interchangeability is less compared to SP as the optimum position for video and hi-fi is closer to each other. The NTSC hi-fi recordings on PAL/SECAM-Drum and play back (PB) on PAL/NTSC and NTSC sets is noted to degrade, and vice versa. Depending on the servo tracking algorithm of the VCR, tracking may be continuous and cause toggling of the audio between hi-fi and linear (mono track) which can be annoying, this can be defeated by manual tracking or switching to linear audio (mono track). The playback of pre-recorded NTSC hi-fi on PAL/SECAM-Drum is acceptable, as the servo software will automatically track to the best compromise tracking position, the unwanted continuous tracking is thus avoided. In short, this is to realise NTSC hi-fi recording and playback with existing PAL/SECAM-type drums (240deg) without compromising video performance ; NTSC interchangeability within European drums is in fact better ; however some slight compromise with Asian or NTSC drums interchangeability is expected. The PAL/SECAM-drum can be utilised for NTSC-hi-fi-recording or playback, with some compromise in SP interchangeability which may occur with actual NTSC-sets. If problems occur, user can switch to manual tracking or to mono which is acceptable. However this is quite unlikely to occur as prerecorded NTSC hi-fi tapes from PAL/SECAM sets is not likely to be used outside Europe. The record and playback interchangeability of NTSC hi-fi with other PAL/SECAM set (that is VCR with PAL/SECAM-type-drum) is not compromised at all as the drums are very similar.

Claims: CLAIMS 1 . Device for recording on a video tape ( 1 ) comprising a drum (2) carrying at least two video heads ( 1 2) and at least two audio heads ( 10) and able to perform notably NTSC-hi-fi-recording, characterised in that said drum (2) is of the PAL/SECAM-type. 2. Device according to claim 1 , characterised in that each audio head ( 10) is situated at an angle of 60deg in the rotation direction (R) with reference to the video heads ( 1 2). 3. Device according to one of the preceding claims, characterised in that the relative height between the audio heads (1 0) and the video heads ( 1 2) is optimised for PAL/SECAM recording. 4. Device according to claim 3, characterised in that the relative height between the audio heads ( 10) and the video heads (1 2) is comprised between 70 μm and 74 μm. 5. Device for recording on a video tape ( 1 ) comprising a drum (2) carrying at least two video heads ( 1 2) and at least two audio heads (10), characterised in that the drum (2) is able to perform NTSC, PAL and SECAM hi-fi recording.

Inventors: DUMONT FRANK, LEE KOK JOO, DUMONT, FRANK, LEE, KOK, JOO
Applicants: DUMONT FRANK, LEE KOK JOO, THOMSON MULTIMEDIA SA, DUMONT, FRANK, LEE, KOK, JOO, THOMSON MULTIMEDIA
Application year: 1999
Main classification: G11B5
IPC codes: G11B5, H04N5