Many of the Sony Beta models had a switch (located on the front or the back) that altered the VCRs electronics so PCM recordings can be played. PCM is stands for Pulse Code Modulation it is a recording system that allows recording analog data, primarily music, in a digital format using video tape as the recording media. To see a PCM processor and find out more go to "Betamax Accessories" or click here. The system works quite well but to work its best the DOC circuit needs to be off for the recorder being used. DOC is Drop Out Circuit and it is used in every recorder to fill in blanks spots in the picture caused by minor imperfections in the tape. Those white and black specks you see from time to time are the flaws that get through but much of the time the DOC takes them out. It does this by repeating the line from above when line below it fails to scan for some reason. When you turn on the PCM switch you are in effect turning off the DOC circuit. The reason this is done is because the when a broken piece of digital information goes by in a PCM recording if the DOC is operating it would send back the line before it which would confuse the PCM processor. So for all the times except PCM recording the switch should be set to off (this turns on the DOC circuit). I think I should mention also that if you set the PCM switch to on and play back your tapes you will notice a larger number of dropouts in the picture. The DOC is not taking them out and even the best of tape has a few flaws for the DOC to clean up. The PCM switches are shown here in the OFF position. ©Misterßetamax go to homepage