Betacam. SP had a horizontal resolution of 330 lines. The BVU 800 series Y-FM carrier frequency was upped to 1.2 MHz giving it wider bandwidth. BVU 800 series also added Dolby audio noise reduction. Sony's BVU 900 series was the last U-matic VTR made by Sony. First-generation BVU-SP and Beta-SP recordings were hard to tell apart, but despite this the writing was on the wall for the U-matic family, due to intrinsic problems with the format. Problems A recurring problem with the format was damage to the videotape caused by prolonged friction of the spinning video drum heads against a paused videotape. The drum would rub oxide off the tape or the tape would wrinkle; when the damaged tape was played back, a horizontal line of distorted visual image would ascend in the frame, and audio would drop out. Manufacturers attempted to minimize this issue with schemes in which the tape would loosen around the spinning head or the head would stop spinning after resting in pause mode for a pre-determined period of time. The format video image also suffered from head-switching noise, a distortion of the image in which a section of video at the bottom of the video frame would be horizontally askew from the larger portion. The format also had difficulty reproducing the colour red, and red images would be noisier than other colours in the spectrum. For this reason, on-camera talent was discouraged from wearing red clothing that would call attention to the technical shortcoming. Copying video from one U-matic VCR to another compromised playback reliability, and levels of head-switching noise, chroma smearing, and chroma noise compounded with every generation. These issues motivated videotape editors and engineers to use work-arounds to minimise this degradation. A time-base corrector (TBC) could be used to regenerate the sync tip portion of the video signal sent to the "recording" VCR, improving playback reliability. The "dub" cable, more formally called "demodulated" (or "demod" for short), was a multi-conductor cable that circumvented a portion of the video circuitry, minimising amplification noise. Uses For synchronisation to broadcast or post-production editing house genlock systems, U-Matic VCRs required a time base corrector (TBC). Some TBCs had a drop-out compensation (DOC) circuit which would hold lines of video in temporary digital memory to compensate for oxide drop-out or wrinkle flaws in the videotape, however the DOC circuits required several cables and expert calibration for use. U-matic