That weird switch which nobody could figure out - Beat Cut!?

stereo systems and boomboxes from the '80s and  '90s are famous for having an overabundance of   buttons dials switches and knobs it may  look intimidating at first but generally   through experimentation and experience you  can figure out what they do except for one it's labeled using ambiguous or  inscrutable terminology and the   vast majority of the time changing its  position has no discernible effect or you   may have not even noticed it because it's  often put on the side or back of the unit   or is combined with multiple other  functions on the same button or switch it doesn't help that manufacturers couldn't  agree on what to call it names for it include   beat cut beat cancel beat proof often  abbreviated to BP or simply just beat   other names for it include ISS OSC BFC  and bias mode and if they are labeled   at all the positions are marked using  meaningless numbers letters or dots this paint splattered GE boombox from  1992 is the only one I have which gives   any indication as to the purpose of  this button but that still doesn't   tell you why do you want to cut the beat  when listening to records in the morning oops and sometimes the owner's manual if you can  even find one for a 30 year old product isn't   of much help either the one for my JVC PC-W222  portable component system says beat cut switch   when recording an AM or SW broadcast beats  may be produced which are not heard when   listening to the broadcast in such case  set this so that the beats are eliminated at least now we know it refers to recording from  AM radio not vinyl before noon but what's the   deal with producing beats? AM radio is better  known for Rush Limbaugh than Grandmaster Flash well as I mentioned this is a case of  ambiguous terminology the beat that   the switch eliminates is not the beat of the music it is referring to a beat tone or  beat frequency like the warbling   effect to hear when you play two  notes next to each other on a piano those strange noises are examples of beat tones a similar kind of beat frequency may be generated  when you have an AM radio tuner and a tape   recorder in the same enclosure "elaborating  so I will elaborate extensively tonight" now in order to have good quality a cassette  recorder needs to add a bias signal to the tape   when recording I'll let VH1's Bobby Rivers  give a simple explanation of how it works "look out now we're going to get a little  technical ever wonder why some tapes are   called high bias? here's the best explanation  I've ever heard bias is a super high frequency   signal that acts like MSG in Chinese food you  add just the right amount and the recording   sounds delicious add too much or too little  and the music is never as tasty as it should   be listen to this recording of Angel Dean and  the Zephyrs made with the right amount of bias" that bias signal is generated by an oscillator  coil such as the one you can see here inside   a cassette deck that doesn't cause any  problems with radio reception when the   cassette deck is in its own shielded metal  box but if I remove the cassette deck's cover and turn on the radio and put  it close to that oscillator coil you can hear a whistle and if I  stop recording the whistle goes away so that poses a challenge when you're designing  something like this stereo system which has a   radio tuner and a cassette recorder in  the same enclosure if I take it apart   and look at the circuit board here is that bias oscillator and down here is the  built-in AM radio antenna and you can see they   tried to mitigate that interference by putting  them at extreme opposite ends of the circuit   board but when you're designing something smaller  like a boombox or especially a handheld cassette   recorder with a built-in radio tuner you don't  have that luxury of keeping the bias oscillator   coil and the AM radio tuner apart from each  other to eliminate that chance of interference so with something this small when you start  recording an AM radio signal you may get that kind   of whistle in the audio so that's why they include  that oscillator switch in this case otherwise   known as a beat cut switch or those other names  I mentioned earlier if you move that switch   you can hear there's no more whistle  if I change it back we get the whistle that interference does not happen on all AM  radio frequencies just ones that happen to   be harmonics of the frequency used by the  bias oscillator and the cassette recorder   it also does not happen on FM because FM  uses much higher frequencies than am and   frequency modulation is less prone to  interference than amplitude modulation however this beat frequency interference can  happen on shortwave and longwave as well not   just the band that some parts of the world refer  to as am which is actually the medium wave band so with the beat cut switch does is it slightly  shifts the frequency of the bias oscillator and   the cassette recorder not enough to negatively  affect the quality of the recording it makes   but hopefully just enough to shift it away from  the frequency of the radio signal you're trying   to record and that's why they give you  several different positions because it   may shift it to to a frequency that happens  to collide with another radio signal so you   get multiple choices so that no matter  what frequency you're trying to receive   one of these choices should be able to  get rid of that beat frequency noise here I'll give a sample of its effect on my Sanyo  stereo system which confusingly labels the beat   cuts which bias mode you may have noticed this  button labeled bias mode but that's a misnomer it   has nothing to do with whether you're recording  on normal or high bias tape as explained in the   manual it says when recording from an AM station  interference in the form of a beat howling or   whistling may sometimes appear in this case  simply set this switch to the other position for example I'm recording from a station on 820  AM and maybe you can hear that annoying whistle   in the background if I push this button the  whistle disappears conversely there are some other   frequencies where you get a whine with the button  pushed in but releasing it gets rid of the whine t here are several ways to avoid the need  for a beat cut switch one is to use DC   bias recording which does not require a bias  oscillator and thus eliminates the problem many inexpensive portable tape recorders use  DC bias because it simplifies the circuitry   and reduces battery consumption compared to  AC bias however as I'm sure you can hear it   also produces recordings that are more  noisy and shrill sounding than AC bias   can get unsuitable for use in  high quality tape recorders "FM 96.7" many stereo systems opted to use an external AM  loop antenna like this which solves the problem by   putting the AM antenna completely outside of the  cabinet where the cassette recorder circuitry is   plus you can rotate it to get the best reception and sometimes even when a system does have a beat  cut switch it's not actually needed such as on   this 1992 GE boombox which as you can see has a  rather large cabinet and I think it has enough   physical distance between the cassette recorder  circuitry and the radio tuner circuitry that   that beat frequency interference does not happen  but yet they included a beat cut function anyway I think this is because it must share the  same circuitry with smaller boomboxes where   that interference would be a problem  and it was simply cheaper to reuse the   same circuitry on this larger model than to  modify it because this one does not suffer   from that problem so it does have a beat cut  switch but it doesn't really have any effect I actually have a real world sample of how a  recording can be impaired by not having the   beat cut switch in the correct position this was  a recording I made back in January 1998 of a new   radio station that just went on the air their  first day on air was January 5th, 1998 I missed   their sign-on but I did get a recording of them at  night that day so I wanted to set my timer on my   stereo system to begin recording the next morning  January 6th at 6 a.m. when they signed on the air I was using a Seiko stereo system just like  this which had a dual cassette deck a radio   tuner and a timer but if we zoom in on this  photo we can see it has a button labeled OSC   which is we know is a beat cut switch and I  neglected to have that in the correct position   when I was recording this radio station  causing a constant whine in the audio so I'll give you a sample of what that  sounded like it starts with Jack Ellery   the morning show host on WJHR talking  about how foggy it was that morning "I was following the guy ahead of me and   that's what you have to do just follow the guy  and I followed him and followed him and followed   about 15 miles and all of the sudden the sucker  slams on his brakes came to a screeching stop   I leaped out and said 'what are you doing!?'  he said 'this is my driveway!' [laughter]   holy crow and all that sort of stuff alright  we are WJHR we're at 1040 on the dial we   are broadcasting from Flemington, New Jersey  covering a good deal of the state of New Jersey" there is at least one new product which you can  still buy today which has a beat cut function   it's the Sony CFD-S70 CD cassette boombox Sony  calls it ISS which stands for interference   suppression switch if I turn it on tune to a weak  AM signal and put in a tape and start recording it maybe you can hear a whine but if I push the  play mode button and change it from ISS1 to ISS2   the whine disappears and you actually  get three different settings here clearly on this frequency ISS1 does cause  that beat noise but changing it gets rid of it I know this topic may be of diminishing  relevance because AM radio is unlikely to   see the same revival of interest as cassette  tapes have experienced in recent years and   in some parts of the world AM radio is  basically already extinct even though   that is definitely not the case here in the  US but I know many people have been puzzled   by seeing a beat cut switch or whatever it's  called on their particular piece of equipment   and they've wondered what its purpose is  and how it works and well now you know

Channel: VWestlife

Views: 416,016

Keywords: cassette, deck, recorder, player, boombox, portable, stereo, system, walkman, recording, am, mw, sw, lw, shortwave, longwave, radio, receiver, beat, cut, cancel, iss, bfc, osc, button, switch, bias, oscillator, frequency, interference, whine, whistle

Id: gm0dT-vi0XU

Length: 12min 56sec (776 seconds)

Published: Sun Apr 02 2023