PPM, like VU, is for *broadcast line level* monitoring. It goes in the studio console or in a radio network switching center. In the US, every place the signal passed from/to AT&T Long Lines from a national network or a local station, both parties watched their VU meter.
VU is the one with costly ballistic movement because in 1938 electronic processing was too expensive for general application in the vast multi-party north american networks. Does not log-scale.
PPM was often done with low-cost meters because ballistics and even log-scale was done in a several-tube amplifier, practical by 1950.
SPL meters are a side-branch with various approaches, mostly more VU-like (sound does not peak-clip). Since LCDs got cheaper than mechanical movements, we have digital, and you never know what they are doing. (One of mine, "slow" means it updates in chunks.)
Ah. I was hoping it would be something really interesting, like Peculiarly Popular Marsupials or Passionate Purple Macaws.
But yes, I'm quite familiar with the concept of analogue signal metering. There was a several-year period in my late teens/ early twenties when I slowly designed and built all the electronics for an entire cassette tape deck, piece by piece.
I certainly couldn't afford "expensive ballistic movements", so I substituted smart electronics driving the cheap VU meters that I could afford. The electronics included a fast active peak rectifier with a long decay time driving the meter movement, and a red LED to indicate the arrival of dangerously big peaks before the mechanical meter could.
The most complicated part was the all-discrete stereo Dolby B noise-reduction circuitry. There were already Dolby B integrated circuits being manufactured, but they were only available to Dolby-licensed commercial manufacturers, not to penniless students like me.
So I scoured the local libraries and eventually found an all-discrete Dolby B schematic in an electronics book, designed a PCB for it by hand on graph paper, etched it myself, drilled all the holes, and built the thing. It worked very well, even though I had to use off-the-shelf JFETs, not the special selected and matched pair I was supposed to use.
It was the RF bias oscillator that gave me the most trouble: I didn't own any kind of meter, so I had to design and build the oscillator without knowing if it was actually oscillating, and then set the bias level entirely by ear, using lots and lots of trial and error. In the end I was able to make recordings that sounded good to my ears, but I never could measure the frequency response to find out what I'd ended up with.
I was very thankful when the CD arrived, and I no longer had to deal with all the numerous failings of tape and vinyl.
-Gnobuddy
I spent much of my spare time in 1969 through 1971 hanging around a couple of the dumpy 3rd rate recording studios in the Miami Florida area. These studios made their money recording radio commercials, and letting bands practice before their "date" at Criteria where their work would be committed to vinyl.
After a whole lot of boredom and practice I got to be known as the "master of the razor blade." This was a skill that quickly lost application and I doubt that many today would even have a clue as to what or why.
The "blade" was used for splicing, and making tape loops with analog tape. It's particularly useful with old mono machines where one audio channel can occupy half, or even all of the width of a 1/4 inch tape. Angular cuts can make "crossfades" which were hard to do by regular means. A lot of fun can be had in a room full of "old junk" which had been discarded by the bigger studios in the area. I had made about a dozen 10 inch reels full of "music" with nothing but my guitar and whatever equipment was available in the studio at 8 AM on the "morning after" one of those practice sessions. None survived poor storage in Florida heat and humidity.
Lets just say that a 10 inch machine left running on 3 3/4 ips in a closet could catch enough of Wishbone Ash to make an Argus bootleg cassette several months before the record was announced.
After a whole lot of boredom and practice I got to be known as the "master of the razor blade." This was a skill that quickly lost application and I doubt that many today would even have a clue as to what or why.
The "blade" was used for splicing, and making tape loops with analog tape. It's particularly useful with old mono machines where one audio channel can occupy half, or even all of the width of a 1/4 inch tape. Angular cuts can make "crossfades" which were hard to do by regular means. A lot of fun can be had in a room full of "old junk" which had been discarded by the bigger studios in the area. I had made about a dozen 10 inch reels full of "music" with nothing but my guitar and whatever equipment was available in the studio at 8 AM on the "morning after" one of those practice sessions. None survived poor storage in Florida heat and humidity.
Lets just say that a 10 inch machine left running on 3 3/4 ips in a closet could catch enough of Wishbone Ash to make an Argus bootleg cassette several months before the record was announced.
My experience is that the PPM has an expensive movement, the VU much looked down on at the BBC, and present on Leevers-Rich tape recorders, showing a substantial under-reading. The VU was regarded as an 'average' reading meter, but often favoured by non broadcasting recording engineers when mixing.
If anything peak clips, it is the VU, I remember illustrating this to a friend in about '75 with my A77, VUs, and he was amazed at the difference.
(This with my special order Ernest Turner PPM movement costing £35 at that time.)
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Late to this thread but cannot help having to reply.
Stupidity was present when I was a yongster 50 years or so ago.
E.g.There was this electrical apprentice (after two years of study) that after having installed wiring in the house asked his boss how to test an outlet to see if it worked OK. (!)
The boss replied tongue in cheek to stick a nail in each side of the jack and hold that, if it gave a tingle then it must be working.... The chap subsequently did this and had a heart atack and died and the boss got charged with manslaughter.
What I do perceive is that with the rise of the computer critical analysis no longer seems to be common. Alsoe what irks me at times is that a checkout operator at a shop no longer counts out the money but uses the till to work out that if something is 80 cents and you give her (him) a dollar that (s)he needs to give you 20 cents back.
What is worse is the rudeness that has invaded our society.
This was discussed a great deal earlier in the thread, and many people (including myself) share your opinion.
Just two nights ago, an 83 year old friend grumbled to me in amazement that he had been to a local shop ( I think it was a 7-Eleven, a North American chain of small convenience stores ), and neither the cashier nor the manager could figure out how much change to give him - the cash register was on the fritz, and the transaction was something like this: my friend handed over a $5 bill to pay for a $4.60 purchase.
Neither of the two store employees knew how to solve that thorny problem, so my friend had to gently explain to them that they owed him 40 cents.
The next problem was that there were no 40 cent coins (!!!), so the store employees didn't know how to give my friend that amount. He had to tell them that a 25 cent coin, a 10 cent coin, and a 5 cent coin actually add up to 40 cents.
The kicker? My friend quit school after 6th grade, at the age of eleven, in 1948. And he never went back for any more education ever after. Yet in his old age he has no trouble doing the basic math that TWO young people with a minimum of a high-school diploma apiece could not manage.
-Gnobuddy
Having worked behind the counter I can say that sometimes you just blank out. The simplest calculation just does not compute. However, it seems to happen much more often on the other side of the counter.
Just a few weeks ago, some guy was paying his purchases in front of me and the sum was something small, let's say 4.60€ and the guy handed the cashier a bunch of coins and asked if that's enough. The cashier replied that he was 30 cents short so the guy handed him more coins and went into full panic mode and just said something like "oh I don't know!" and as soon as the cashier took something that seemed like 6€ in coins and was about to give him the change, the guy just stormed out the shop leaving the change there.
Does this mean that the guy was stupid? No, it means that he gets anxiety attacks. That is to say that what we often perceive as just being stupid and/or weird is just a meltdown.
Just a few weeks ago, some guy was paying his purchases in front of me and the sum was something small, let's say 4.60€ and the guy handed the cashier a bunch of coins and asked if that's enough. The cashier replied that he was 30 cents short so the guy handed him more coins and went into full panic mode and just said something like "oh I don't know!" and as soon as the cashier took something that seemed like 6€ in coins and was about to give him the change, the guy just stormed out the shop leaving the change there.
Does this mean that the guy was stupid? No, it means that he gets anxiety attacks. That is to say that what we often perceive as just being stupid and/or weird is just a meltdown.
Even in 1938, a proper VU meter cost $50, maybe 30GBP at the time. Last time I saw a proper (usually Weston) VU it was over $200.
The core of a PPM is less sensitive and the timing specs much less tough; all this is moved into the electronics.
I have no doubt you can find *very* expensive PPM meters. Some of the light-mirror types are marvels of fine machinery. (There's no such variety of good VU meters, only Proper, cheap, and cheaper.)
Blanking on calculations? How could anyone be stupid enough to let that happen? Now give me a second to go look up the integral of 1/x
In all seriousness, I lost a bunch of points on an exam the other day because I wrote down c^2 as being equal to 3E16.
Could have been worse. Back in MY day there were professors who would get quite irate and do far more than dock you a few points for messing up on fundamentals. ”well, Mr. (insert last name here), you just FAILED MY CLASS!”
And about being put on the spot.... anyone here remember the ancient earth custom called the POP QUIZ? And actually having them count for something.
And about being put on the spot.... anyone here remember the ancient earth custom called the POP QUIZ? And actually having them count for something.
As with many youngsters, I did extremely bad in my first pass at college circa 1971 -1972. I reached the point of "academic probation" in 1972, so I quit and got a job at the Motorola plant about 30 miles away.
I started pass #2 at college about 20 years later. I tried to negotiate with the Dean of Engineering to exchange some of the "batteries and resistors" classes that I didn't need, for some basic algebra classes that I DID need.....I failed in the negotiations, so Motorola paid over $600 each for a couple electronics classes that I attended twice each, for the mid-term and final exams. I received perfect scores on all.
Unfortunately things did not go well in Calculus 1 where I received a 55% on the first test, with a note from the teacher that read," You might understand the calculus, but you don't have a clue about algebra." As the papers were handed out, he looked right at me and proclaimed, " Class, zero divided by zero is NOT zero! How could you think such a thing?" I stared him down, and replied "I be stupid." I wound meeting the teacher on Saturdays for some remedial algebra education, and eventually meeting at his house which was near the Motorola plant.
It was there the I discovered his passion for model trains, so I taught him how to automate some of them with 68HC11 microprocessor chips. I had the same teacher for all of my math classes, and for all 3 years of college, I signed my math papers with "I.B.Stoopid."
I remember that most students feared them since there was no chance to "study." Studying for a test was a practice that I rarely engaged in. In fact many times I didn't read or even buy the test book. Math and programming classes were usually the only exceptions.....you can't get good at either without practice.
Now they're too worried about their RateMyProfessor score and course evaluations to do that kind of thing... though sometimes when they get tenure it can be a race to the bottom.
Sure. To err is human, and all that. Most of us have probably experienced a moment of wheelspin when our brains just refused to function for a few seconds. In the middle of a completely routine examination decades ago (I think in high school), I remember, for several seconds, being unable to spell the word "jack" in a sentence i was writing, and marvelling at how that was even possible. That was the first time I'd experienced anything like this, and I was so shocked that all these years later, I still remember that this happened.
However, consider: in the case of the story my friend told me about the 7-Eleven employees, (a) there were TWO people trying to solve the problem collaboratively (b) Neither of them could subtract $4.60 from $5 over a span of a few minutes, and (c) Neither of them could figure out what coin face values added up to 40 cents.
It's relatively rare for one normal brain to freeze for a few moments. Probabilistically, its astronomically rarer for two normal brains to simultaneously freeze, for several minutes, over a problem requiring only elementary-school math skills to solve.
These two people also had a pile of coins and bills in front of them; they could even have solved the problem by addition, if they couldn't manage subtraction. Plunk $4.60 down on the counter, and add coins by trial and error until you reach a total of $5.00; the coins you added are the amount of change you need to give your customer.
But if you don't have a conceptual grasp of basic arithmetic, or how it applies to physical money, you don't have any hope at all of even realising that there is more than one way to successfully solve this particular problem.
And that, it turns out, is one of the downsides of using a credit card or your smart-phone to make every payment: if you never deal with actual currency and coins, you never learn at an early age how numbers add and subtract. But when Mom gives you a $5 bill when you're 8 years old, and asks you to run to the little shop a half-mile away, and bring her back a few onions for that stew she's making, you learn quickly what $5 means, and how to check if you got the onions at the right price, and got the right change back from the shopkeeper.
(Yes, there was a time when $5 could actually buy you onions, and eight year olds were considered competent enough to walk to the nearby store and buy a few things for Mommy!)
That one's pretty easy to remember once you realise it's connected to so many fascinating real-world problems. Any time dx is directly proportional to x - the change is proportional to the quantity - you get an exponential (or logarithmic, depending how you write it) solution for "x" once you've integrated (dx/x).Now give me a second to go look up the integral of 1/x
Physical processes like this are everywhere - water draining out of a bathtub (rate of flow proportional to height of water in the tub), a capacitor discharging through a resistor (current proportional to amount of charge in the cap), a fish population declining by a fixed percentage per year due to overfishing or pollution, a radioactive substance decaying at a rate proportional to the amount of radioactive material present, a beam of sunlight penetrating through layers of sun-screen on your skin and being attenuated the same amount by every micron-thick layer, water-hyacinth growing to cover the surface of a lake, the area occupied increasing by a fixed percentage every day...so many fascinating real-world problems, all of them solvable if you remember the integral of 1/x!
Did you lose the points for not squaring the "3", or for not mentioning the units - (metres squared per second squared) - in your answer?In all seriousness, I lost a bunch of points on an exam the other day because I wrote down c^2 as being equal to 3E16.
The first of those is an easy mistake to make. I agree that it's quite easy to accidentally forget to square the mantissa even though you remembered to square the exponent. But if you also made the second - omitting the units - that was a major error that renders your answer utterly meaningless. Because c^2 is actually 3.47 E10 - if you're working in miles per second and miles squared per second squared. And c^2 is actually exactly 1.0000e0 - if you're working in units of light-years per year, as astrophysicists do!
In fact, any number is the correct value of c^2, if you manufacture the appropriate units.
And that's why it's absolutely crucial to state the units you're using as part of your answer.Over the years, I've had many students who couldn't understand why an answer was meaningless without stating the units used. To help them understand why this was important, I used to ask, how would you feel if someone offered you a job that paid 50,000 a year - and then later you found out that this person meant cents, not dollars? Would you work happily for only 50,000 cents per year, which is only $500 per year?
Now what are the odds that you can get either of those two 7-Eleven employees - the ones who couldn't make change from $5 for a $4.60 purchase - to find the mistake you made when you squared the value of "c"? If you can do that, I will agree with you that we've maligned them unfairly, and they actually have normal math skills.
-Gnobuddy
My experience of further education in the new millennium have been mixed.
I can appreciate some of the feeling that standards have slipped, and in some cases agree that it is just. My experience has been a lot of retired professionals, design engineers, but by far in the majority are young PhD grads, lecturing before and after research assignments. These guys are very very smart, but perhaps not the most natural teacher.
My communications lecturer was a young woman, younger than me, and her prior to lecturing, she was part of a research team working with ultra high speed laser data transmission in orbit, If my recollection is right I think with ESA.
My electrical principles tutor was a wildly intelligent octogenarian, who in another life had worked on data acquisition systems for ICBMs that could communicate to remote listening posts, even during the EMP aftermath of a detonation.
My university have strong links with Rolls Royce Aero, JLR group.
I dont think standards have dropped, but theres always those lecturers, and students of course, that are just "going along for the ride"
I totally agree with your feeling about the bad feeling a cashless society gives me
I can appreciate some of the feeling that standards have slipped, and in some cases agree that it is just. My experience has been a lot of retired professionals, design engineers, but by far in the majority are young PhD grads, lecturing before and after research assignments. These guys are very very smart, but perhaps not the most natural teacher.
My communications lecturer was a young woman, younger than me, and her prior to lecturing, she was part of a research team working with ultra high speed laser data transmission in orbit, If my recollection is right I think with ESA.
My electrical principles tutor was a wildly intelligent octogenarian, who in another life had worked on data acquisition systems for ICBMs that could communicate to remote listening posts, even during the EMP aftermath of a detonation.
My university have strong links with Rolls Royce Aero, JLR group.
I dont think standards have dropped, but theres always those lecturers, and students of course, that are just "going along for the ride"
I totally agree with your feeling about the bad feeling a cashless society gives me
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I was withdrawing some cash from an ATM when a passing friend said hi. Halfway through typing in my PIN I blanked. In the end I had to go home cashless!
There are integrated circuits which provide most of the essential control circuitry required to design and build a switching power supply. This simplifies design and provides an SMPS designer a tested and reliable control architecture.Gnobuddy said:
SMPS control integrated circuits can be avoided and the individual building blocks made from discrete opamps and comparators. What is required is a stable triangle wave generator, a filtered error amplifier, a fast comparator and a switching MOSFET driver stage. Success depends on controlling switching parasitic voltage spikes and on preventing the output voltage feedback path from oscillating. Limiting the bandwidth of the error amplifier and reducing its response speed helps achieving a stable feedback path.
SMPSs are interesting to build, but the process is expensive in both time and money.
That one's pretty easy to remember once you realize it's connected to so many fascinating real-world problems. Any time dx is directly proportional to x - the change is proportional to the quantity - you get an exponential (or logarithmic, depending how you write it) solution for "x" once you've integrated (dx/x).
Physical processes like this are everywhere - water draining out of a bathtub (rate of flow proportional to height of water in the tub), a capacitor discharging through a resistor (current proportional to amount of charge in the cap), a fish population declining by a fixed percentage per year due to overfishing or pollution, a radioactive substance decaying at a rate proportional to the amount of radioactive material present, a beam of sunlight penetrating through layers of sun-screen on your skin and being attenuated the same amount by every micron-thick layer, water-hyacinth growing to cover the surface of a lake, the area occupied increasing by a fixed percentage every day...so many fascinating real-world problems, all of them solvable if you remember the integral of 1/x!
Did you lose the points for not squaring the "3", or for not mentioning the units - (metres squared per second squared) - in your answer?
The first of those is an easy mistake to make. I agree that it's quite easy to accidentally forget to square the mantissa even though you remembered to square the exponent. But if you also made the second - omitting the units - that was a major error that renders your answer utterly meaningless. Because c^2 is actually 3.47 E10 - if you're working in miles per second and miles squared per second squared. And c^2 is actually exactly 1.0000e0 - if you're working in units of light-years per year, as astrophysicists do!
-Gnobuddy
No, in this case it was an intermediate step (modern physics exam) and it was a case of carelessly forgetting to square the 3.
1/x and ln(x) are certainly ones to remember. I will say, however, that if you google "derivative of ln(x)", this is the top answer:
"The derivative of ln(x) is 1/x, and is actually a well-known derivative that most put to memory."
Appropriately sassy.
Yeah, an easy mistake to make by accident.
FWIW, if you had been my student, you would not have lost lots of points for that, depending on how complex the entire problem was. If the c^2 calculation was only a tiny part of a bigger and more complex calculation, I would only have taken off a teeny bit from your score.
On the other hand, if this was a 7th grade test specifically on scientific and engineering notation, and the entire question consisted of "Calculate the square of c, the speed of light, given c = 3 x 10^8 m/S^2", then I would have given you zero marks for the answer c^2 = 3 x 10^16 m^2/S^2...which would be entirely fair, as the question is intended specifically to find out whether the 7th-grader can square a number in scientific notation and come up with the correct answer - and in this case, he/she didn't.
No exam can ever be flawless, but a bit of reasonableness from both student and teacher goes a long way.
These days, of course, the 7th grader would be given a smiley-face grade, a dolphin-safe candy bar, and an animal-cruelty-free gold sticker, no matter what answer he/she came up with.
And then he/she would go on to working at the 7-Eleven, and not being able to make change for a $4.60 purchase paid for with a $5 bill.
-Gnobuddy
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