Very few Betas are equipped with linear stereo. This added capability was mostly limited to the Sony professional Betas, models that included the GCS-50, SLO-323, SLO-325, SLO-383, and SLO-420. It was also used in the SLO-1400 and SLO-1800 production duplicators designed for replicating studio movies, music videos, and institutional materials. The GCS-50 and SLO-1800 were also SuperBetahi-fi stereo models that also had linear stereo (see below). The GCS-50 was the only model that permitted recording separate audio information on the two linear tracks independent of the Betahi-fi stereo. The SLO-1800 professional duplicator was originally released with linear stereo audio tracks in addition to the Betahi-fi. Presumably this was done to accommodate the Marantz VR 200, which was introduced just prior to Betahi-fi. Sony later altered the SLO-1800 and removed the linear tracks. This was probably done to save cost, and because so few consumer machines could actually use it. This didn't exactly thrill Marantz. They never introduced another Beta VCR with their name on it. The VR 200, was manufactured for them by Sanyo (for more of that story, click here.) Linear stereo is different from Betahi-fi. It is electronically recorded inside the video signal using a special FM modulation system invented by Sony. Linear stereo is recorded by two stationary audio heads stacked on top each other in the upper area of the ACE assembly. This is where the top edge of the tape passes by and is normally where the monaural audio is recorded. ACE is short for Audio, Control pulse and audio Erase. To see the assembly, click here. (Opens a panel from the BETA REFURBISHING section.) These two recording and playback electromagnets heads are just like the ones used in reel-to-reel audio recorders. A magnetic signal is recorded on or read from the tape as it travels past these stationary metal heads. For Beta monaural recording there is only one single audio head. Note: A recording is alway made using the linear head(s) for compatibility with monaural only machines. Betahi-fi stereo on the other hand, is recorded elsewhere. It is in located inside the picture signal being recorded by the spinning video heads. This feat was accomplished by making a slight alteration in the video signal called reformatting. Here the luminance part of the broadcast signal is moved up slightly in frequency (400 MHz) to make a space available for inserting four FM carriers for recording stereo sound. Two pairs of the carriers are placed here, two for the left and two for the right channel. Duplication of the channels assures that any minor flaws in the tape would be accounted for. As long as everything stays in place, the FM audio doesn't disturb the video information. Due to the high speed recording taking place using the spinning heads (an incredible 30 inches per second), this system produces nearly perfect stereo. Annoyances like wow, flutter, and tape noise are virtually eliminated. Beta could do this because of its bigger video drum, which produces a longer, stronger, cleaner, fuller, magnetic signal than VHS. Their system could not duplicate Betahi-fi because there wasn't enough room in its video signal to insert any additional information. Their smaller drum cramped their video so much they had to resort to imbedding* their audio to get similar result to Betahi-fi. It was an add-on and it performed well as long as the tape was new and not played too much. To open a panel on the possibilities when using linear stereo, click here. To go back to the description page, click here.
*Imbedding was a method used by VHS to duplicate Sony's Betahi-fi stereo process. This method also took advantage of the high writing speed of the video drum to produce decent fidelity. With this system, two additional audio heads were added to the spinning drum. These extra analog heads were in addition to the existing video heads or any trick heads used. These heads recorded two analog signals just before the video heads came along and recorded over them. It could work because the two types of signals were magnetically different from each other, plus the video heads didn't completely erase the previous audio recording. When played back, the video circuitry reads the picture information, and the spinning audio heads see the analog recording. Alignment was imperative with this system in order to get everything to cooperate. That feat was mostly accomplished by the precise placement of the various heads in the drum during its manufacture. Since the two magnetic signals are different, they can be adjusted separately. In practice, the particle strength and penetration had to be deep in the tape so the video didn't erase it. This required high-quality videotape. This strong magnetic force could cause distortion, and this had to be accounted for in circuit processing. The audio could get erased and weaken over time and could eventually disappear. For this reason stereo was also recorded by the VCR using two stationary linear heads located in the ACE assembly. If the hi-fi should fail, the VCR would automatically switch to the dual linear audio tracks as a back up. This was especially helpful for rental facilities where their tapes got a lot of plays. |