EEVblog

[@AstralS7orm]

Gotta know your sinc. Your scope at least has zero order hold ("disabled") I hope too, in addition to linear? (Bars instead of tiny dots. Or fat dots.) One thing I'd love to see is ZOH with error bars from sinc ringing as estimate, like a blurry overlay. It's a rare case that your clock is perfectly synced with signal. Old analog scopes naturally did that with faded display due to capacitance in memory and display... Though that can lie too, it's exponential interpolation - Laplacian it's called I think? Using a scope as a frequency counter over sample rate only works if you average enough samples. (Or take a long Fourier spectrum, similarly.) Not quite what you showed.

[@EEVblog]

Hmm, an overlay would be an interesting feature...

[@PiezowDimD]

Drawing 2px points over the interpolated line would also help, once there is few enough samples.

[@johnyang799]

Sinc is always better. Because you need to know how capable of your scope, when the case in this video, the scope is essentially store too less samples the equivalent sample rate is too low to reproduce the original signal which is pulses(very high frequency contents) Sinc is guaranteed to not creat high frequency sampling noises and it's inherently limited by the sample rate. You can't get information above your Nyquist frequency. That's why sinc is useful. The misconception here is that it looks like it's "adding" things in timr domain here. But actually it's the cleanest in the frequency domain. No noises/ false information over Nyquist frequency.

[@johnyang799]

@@PiezowDimD That's called oversampling right?

[@EEVblog]

In this case the pulses are not "very high frequency content", the scope simply didn't have the memory/sample rate at that particular timebase

[@pamersiel]

The ringing BEFORE the signal is a screaming sign, that we see artefacts of digital signal processing.

[@EEVblog]

Indeed, I should have mentioned that.

[@leocurious9919]

The individual voltage measurements should simple be visible as dots or whatever once you zoom in enough that they get sparse.

[@unfa00]

Isn't that just the Gibb's effect due to a lowpass filter bandlimiting the signal?

[@Zonkotron]

@@unfa00 A real world normal first and second order low pass filter does not cause that because a real filter is causal and the largest phase difference possible is 90/180 degress, way insufficient for multy period pre ring. No ringing before the pulse arrives for simple real filters ! If you have a transmission line or some other thing with huge phase delay and dispersion, then you can probably generate this in analog too, in the sense that everything will be delayed multiple periods and therefore causal pre ringing is possible with the ringing delayed less than the bulk of the signal... That signal theory stuff....yeah, i think an ideal lowpass would cause gibbs ringing of the sin(x)/x type, but an ideal filter is kinda bullshit. No such thing. Can probably be approximated and has some real world use, otherwise they would not teach it. Digital signal processing throws it all outta the window. Fourier transform based fast convolution and similar stuff is usually not causal and generates all sort of hillariously comical signals that are totally impossible in reality, which is of no concern if you are processing a prerecorded signal where the future is known....

[@pamersiel]

The key point here is that in digital processing we can easily create something that looks like looking ahead to the future and as a result, the impulse response will be symmetrical along the time axis. In analogue circuitry, this is also possible, but it will cost a gigantic heap of samplу-and-hold capacitors or delay lines and other circuits.

[@simondalzell1965]

It's the reverse of the problem audiophiles have! Some look at linearly-interpolared digital audio samples and assume they're getting a "blocky" audio output. Then they look at the sine interpolation and complain about those wiggles around a theoretical square wave and think that's an artifact of converting analog to digital. Great demonstration in an obvious place that I'd never considered.

[@electronash]

Yeah, it demonstrates a basic misunderstanding of Nyquist / Dirac theorem etc. Mathematically, if the output filter after the DAC is decent, the resulting waveform should be an exact representation of the original input (below Nyquist). (given the limits of the dynamic range, and noise floor etc., which is mainly a function of the bit depth, and almost inaudible even when using 16-bit samples). Technology Connections did some superb vids on this subject. I'm guessing you've already seen them? :p (but for the benefit of anyone else reading this)... kzbin.info/www/bejne/pojNlYp5mrWarKM kzbin.info/www/bejne/mXq0anyOiLqtq68

[@johnyang799]

@@electronash It should be exact if the clock is synchronized. If not the shifted t0 will cause real world issue. So 5 times is mostly the way to go. However in audio, our ears don't have clock or synchronization so it shouldn't matter. But who knows. ____________________________ When we don't exactly know something, it's better off over doing it rather than ignoring it. When digital filter plays a role why not just oversample 2 to 4 times to avoid artifacts.

[@electronash]

John Yang Yes, I agree. If you really want the best possible audio, then go with something like 24-bit / 192 KHz. But even 44.1 KHz audio CDs sound pretty great to 99.9% of the population. They are more than "good enough" to the majority of music lovers. Nothing is going to be perfect in any recording medium, of course, and I completely get why people collect and enjoy the older formats too. I mean, this vid is about digital oscilloscopes and sampling, but it is closely related to digital audio. I'm trying to avoid getting into the whole "audiophile" discussion too deeply, though, as it's been discussed to death, and people can get quite religious about it. lol

[@GoldSrc_]

Have you seen Digital Show and Tell by Monty Montgomery explanation of digital audio here in youtube? it explains that perfectly. I love to show that to audiophools who think their hearing gets better with age lol.

[@johnyang799]

@@electronash Agree

[@Pops180]

Keep these scope vids going. I teach an electronics class at work to green engineers and you seem to explain things a lot better than I can.

[@BruceNitroxpro]

If only we could supply the field with people like this, there would be a lot more digital scopes being used correctly.

[@HighestRank]

If only we could supply a confuser to all the peoples fields.

[@richb313]

I always explained to my techs you have to be smarter than your test equipment because if you are not they will lie to you with great regularity.

[@MrKristian252]

This thumbnail got me

[@musashi939]

That's a penis!

[@enricotrudu6760]

Maybe from a Diktronix scope

[@AlexanderBukh]

16:27

[@3dlabs99]

It's a trap using the "it's a trap" reference

[@PeregrineBF]

I wouldn't call sinc "smoke and mirrors". The Nyquist-Shannon sampling theorem derivation requires convolution of the sampled values with an ideal sinc function to recover the original signal. The reason for the 4x instead of the 2x limit is because of the finite number of samples and the finite (non-ideal) sinc function used. Just as the Fourier transform is only valid for infinitely repeating signals so real systems use windowing functions which add some distortion. It's important to know what the differences from the ideal case are to interpret any measurement.

[@EEVblog]

It was just a turn of phrase, meant to explain that something tricky is going on. I explained how it's mathematically correct.

[@PeregrineBF]

@@EEVblog I assumed you knew, but wanted to elaborate on it a bit. Give people the terms to search for and all, with spellings. I suppose I phrased things badly.

[@johnyang799]

@@EEVblog On the other hand when it's on you'd know something's wrong then you can zoom in. Otherwise you'd end up using linear without knowing there's something between the samples.

[@stevewhite6252]

The same problem occurs for inexperienced DSP engineers in using FFTs for spectral analysis. Various window functions can be selected depending on the signal and sample rate. I have seen numerous cases where engineers told me that a spectrum they were examining looked distorted but what they were actually seeing was the effect of the particular window function selected.

[@Hyxtryx]

How does having a finite number of samples on a CD audio track affect the resulting waveform? Does that add distortion that wouldn't be there if the audio were sampled at 88.2 KHz instead of 44.1? Or, better stated: Does the distortion introduced by not having an infinite number of samples in a 44.1KHz audio track show up in the audible range?

[@RedwoodRhiadra]

The Oscilloscope Interpolation Trap - best Robert Ludlum novel ever.

[@friedmule5403]

10:00 Genius illustration in upper right corner! Now I think that I really understand what FFT is. Thanks Dave! :-)

[@calebr4961]

... borrowed directly from Wikipedia: en.wikipedia.org/wiki/Fourier_series

[@BertieJasokie]

AvE and Dave mashup = dAvE. Do it!

[@leocurious9919]

AvE is still around? Stoped watching his videos when they got super boring and the only content was his voice.

[@daverhodes382]

@@leocurious9919 Several hundred thousand views per video? Perhaps you should stick to kids cartoons.

[@UpcycleElectronics]

Not everyone watches YTbers that are so loose with the foul language. Some of us have kids around. I watched AVE in the past but I'm not interested unless he goes clean.

[@BertieJasokie]

@@leocurious9919 Maybe we take you apart and see if your insides are skookum.

[@BertieJasokie]

@@UpcycleElectronics Better they learn it from that guy on youtube than on the streets from some wankers and gangbangers. Lol

[@Der_Arathok]

Watching this literally 2 days after checking a signal and taking data from the oscilloscope that "didn't make sense"... I always thought, the oscilloscope is always right! Greatly appreciate this Video! A must watch for people having to use a oscilloscope in a lab maybe as scientific helper and just started out. I wrote the link down for my fellow students!

[@EEVblog]

Everyone gets caught by this eventually!

[@Chris_Grossman]

I always maximize the memory and check the sample rate before I zoom in. On my SDS1102X the slowest sweep that will capture at 1 Gs/s is 1ms/div with the full 14M memory depth turned on. It is great for zooming in on the scope, but gives you a vary large file if you want to save the data.

[@EEVblog]

Yeah, but you have to know that and do the mental calculation and keep track

[@Chris_Grossman]

​@@EEVblog You can just watch the sample rate indicator as you adjust the sweep rate. If it drops below 1GS/s your sweep is too long, or you do not have the memory set long enough. You don't need to do it in your head.

[@greenlight04]

Basically this is just sampling theorem. Multiplying with delta pulses in the time domain (equals the sampling process) means folding in the frequency domain. If you want the analog signal back you filter in the frequency domain with an ideal rectangel to get only the low frequencies up to the maximum of 200 MHz limited by the bandwidth of the analog frontend (and not the ones that occured as copies of the real signal at higher frequencies due to folding as an effect of sampling in the time domain). This rectangel in the frequency domain corresponds to folding in time domain with sinc aka. Use a sinc-wave for every point in the time domain. If you have too low sampling the frequency copies due to the sampling interfere with the original low signal-frequencies. Trying to filter out the original signal with the ideal frequency rectangle filter aka. Sinc-interpolation in time-domain is not possible anymore and you get nonsense. The time domain sinc is therefore just coming from the ideal rectangle frequency filter. Flies away.

[@wpherigo1]

Which is why it’s always a great idea to have 2 ways to measure something, with one of them being analog. You can best understand these issues if you’ve done time with analog scopes before, and understand how digital scopes work.

[@radoslawbiernacki]

Great video. This is the proper way of explaining what is the bandwidth and sample rate of oscilloscope.

[@rabbibacongrease88]

This is probably the most informative video on this subject that's ever been made. Great job and keep up the good work.

[@PlasmaHH]

I don't know anymore which scope it was, but I once had my hands on a scope where when you zoomed in enough, it would display little dots in addition to the line. I really loved that and thought that this should be a default on all scopes as it immediately makes you aware of such situations.

[@EEVblog]

That rings a bell, but I can't remember

[@udhayakumara4033]

Dave, you got a new oscilloscope SDS5104X. Can you please do a full review video and if possible compare with keysight and Tektronix. I had a plan to purchase this earlier because it's a decent spec 1GHz oscilloscope in the market with very lower cost. I don't believe in the marketing videos and I looking for your opinion on this.

[@kalhana1]

real trap for young players newfangled come-a-gutsa chase a red herring down a rabbit hole

[@leocurious9919]

Whats this other thing... sometimes when he doesnt know he says "bjurla, bjurla" or whatever? How to google something like that? ;D

[@dentakuweb]

@@leocurious9919 He's saying Bueller. It's a reference to Ferris Bueller's Day Off. www.imdb.com/title/tt0091042/

[@UpcycleElectronics]

Thanks. Because you spelled it out, I finally looked up: *come-a-gutsa* (UrbanDictionary) "Verb. (Australian colloquialism) To be thrown off a moving object at high speed, arms and legs flailing, landing on a hard surface and sustaining multiple wounds and broken bones." This is the only one he says that I just totally ignored...for the last 4+ years I've been watching...Funny, the injury that disabled me and got me into hobby electronics fits the definition perfectly.

[@lorenkuhn3806]

Good (expensive) scopes should maybe show a warning that your zoom is greater than $sensible_sampling_rate_interpolation.

[@iamdarkyoshi]

Thumbnail has a crude representation of a gentleman's sausage. Brilliant.

[@HamiltonMechanical]

I just bought my first oscilloscope! I'm so excited! I bought an auction lot with 7 oscilloscopes, a couple function generators, and a few digital power supplies. Can't wait to get ahold of them and see how many of them still work!

[@henke37]

There is an easy solution that avoids this issue while also letting the marketing people invent higher numbers. Just mark the actual samples on the plot!

[@wigrysystems]

You are the saver of the day. Another day I was making captures at 500ms range and then zoomed all the way down to 50us and there should be steady 2% PWM switching at 2.5us interval and it was all spotty and I thought that is my algorithm wrong, is it really missing the switchings. Now I know that I need to be aware of the sample rate and memory depth. Also the interpolation thingy is a really good to know. Well scope novice here anyway. Thank you a lot for explaining, the knowledge landed on a good soil :)

[@EEVblog]

Everyone gets caught by this eventually!

[@XpressCrosSs]

In short, it just treads sampled data (represented as dots) as impulses and replaces them with sinc function for better reconstruction. This is how basically ADC's work. In a practical situation, sinc function is a square wave. It is called zero order hold. It is widely used in PWM technique. According to Sampling Theorem, data should be sampled with frequency twice time higher than max. freq. component of the signal. If you dont, signal is distorted. That is what happens in the video.

[@johnyang799]

You are mixing stuff up. Sinc can in either time domain or frequency domain. The pulse is in the other domain. In this case sinc in time domain and brick wall in frequency domain.

[@OfflineSetup]

Surely it should always overlay the dots (actual measurements) over the interpolation, to demonstrate its "guessing".

[@juliannesermon8057]

The whole "deep memory" thing seems like a trap for young players... why does it allow you to zoom in beyond what can be reliably rendered from the available data?

[@KuraIthys]

I get annoyed by scanners and cameras that do it too. Especially since they often make a concerted effort to obfuscate what the actual resolution limits of the sensor are. (Especially scanners - my scanner is something like 1200x600 DPI, yet the software just goes up to 3600 dpi and makes absolutely no mention of which, if any of the settings produce an interpolated image.) Interpolation, especially without explicit warning that it's being done really can be frustrating sometimes...

[@denny9931]

Yep, fell for that once or twice too, but it´s the way it is, sample memory is either expensive or slow. Going for logic analyzers however does not help when trying to see signal quality. Throwing money at the problem by even higher bandwith scope is not for most hobbyists. The good thing is that MSOs get better and better and you can check signal quality and have data interpretation in one device.

[@closure4791]

The interpolation issue has nothing to do with deep memory. Deep memory is amazing and awesome.

[@juliannesermon8057]

@@closure4791 But do you know the answer to my question?

[@dhpbear2]

Great video, Dave! Even my lowly audio editing program (Cooledit 2000) employs this Sin(x)/x processing.

[@gudenau]

Technology Connections has a video about this, it's just focused specifically on audio.

[@autogolazzojr7950]

I remember that video. Only difference here is that there isn't an upper limit like in human hearing, so aliasing is fair game in digital scopes. Better use peak detect to not worry about aliasing.

[@xx3868]

Thats why i love using an old analogue scope. you get what you see - no digital processing and traps and missing spikes which you need to see when looking for glitches..

[@IC2MpolytechLille]

Good video about an overlooked aspect. The 500GS/s advertised in the data sheet is acquisition interpolated sample rate. These samples can be saved, while display interpolated samples cannot. They are meant to fill up the screen pixels to get a continuous signal.

[@KissAnalog]

Great video Dave on a great subject!

[@TheDefpom]

I don’t suppose my Siglent bandwidth hacking video prompted this did it? Just seemed similar as I had also used dot mode to demonstrate the actual samples captured.

[@BruceNitroxpro]

As I used to say to newbies in the field of EE, "Those who know the most math end up as boss."

[@qzh00k]

those that even knew the math existed were half way there, some became the boss.

[@BoydWaters]

The good old days of the Peter Principle. Has long since been replaced by the Dilbert Principle. :-)

[@kenvez9309]

Great presentation - you're a natural teacher..

[@jtsotherone]

I think AvE and Dave are slowly converging into one entity, they are sharing the same vocabulary these days. No bad thing!

[@DrakkarCalethiel]

jtsotherone That confusor made me laugh!

[@BlackEpyon]

Well, I know what he's going to call the next oscilloscope that blows up on him.

[@victornpb]

They are slowly developing their own language, in 50years you'll need to learn Aveev to study engineering.

[@theantipope4354]

Hey, it's fine by me!

[@TestECull]

This video is basically a 17 minute long advert for having a fully analog scope on your test bench alongside your digital one. This won't affect a pure analog scope as they don't have interpreters to begin with.

[@leocurious9919]

So how does it connect the "dots"? Not in a "curvy" way? Yes, I know, they are not individual "dots". Just get to the point what the signal looks like. I doubt that it would be any better.

[@TestECull]

@@leocurious9919 Analog scopes don't draw dots at all. Analog scopes amplify what you're probing, then use that to drive the deflection yokes of a cathode ray tube display. That, in turn, magnetically deflects a stream of electrons that excite phosphors on the screen. That's what makes them analog; They show you exactly what comes into them. They don't have quite the capabilities at super high frequencies, but on the flip side, you won't get bitten by sampling errors. That's why you should have one on your test bench *alongside* a digital scope. You want both. Both can do things the other cannot, they compliment rather than replace.

[@johnyang799]

@@TestECull Analogue also has limited bandwidth. And when that happens it's way more ugly than sinc interpolated digital scope.

[@johnyang799]

@@TestECull One digital scope is good enough. Analogue scope doesn't help anything.

[@MrGurkentomate]

Awesome to see fourier transforms/series in action, basically never heard of them before a course i took last year in university, now I see them everywhere. If you want to get a deeper introduction into fourier transforms watch 3blue1browns video "But what is the Fourier Transform? A visual introduction"

[@Jajaho2]

Actually fell for that when probing an I2c line.

[@EEVblog]

Happens to everyone

[@Jajaho2]

@@EEVblog I feel better now ;-)

[@MAYERMAKES]

I actually encountered this phenomenon a few months back and it tripped me, I thought the serial data was not transimtted correctly. Reflashed the chip measured again. Now I know what was really going on. thanks that is very helpfull!

[@EEVblog]

Very common issue!

[@marioverruso4576]

EEVblog Dave, Interpolation is/was not used on analogue CRO's, like the Tektonix 511 (or 547 if you wanted dual beams.) simple reason is they don't need it, because they display the whole timeline not discrete samples. Modern sampling oscilloscopes use interpolation to display a pretty waveform, and as you correctly point out, this can provide misleading results. This can lead you astray if you are chasing spurious signals, ringing etc that is occuring at the upper limits of the oscilloscopes bandwidth, you most likely will miss it, but with the old analogue CRO,s you still got some visual indication that something was there. Obviously the old CROs had their intrinsic issues, like persistence and brightness at higher speeds, blooming and burnt out screens, plus they were heavy and fragile, and forget about signal capture, that was done with a special polaroid camera attachment, but, they did have their advantages.

[@3dlabs99]

Would be helpful if the scope showed the sample points when the distance between them goes over a certain threshold. Like with a cross or a circle on top of the interpolated graph.

[@qzh00k]

You are right on the edge of high energy analysis and imaging, just on the other side of "It's Complicated".

[@Lucien86]

What you are seeing is a form of aliasing error, a real curse of all digital sampling... If you don't know to look it catches you out so easily, anything could be hidden between the dots..

[@autogolazzojr7950]

In this case, peak detect is your friend. That is, unless your signal has components of higher frequency than the max sampling rate.

[@adamp9553]

With sinc you're seeing the signal with a band limit. It's a form of antialiasing that would reflect what you hear if played back as audio as nature has frequency responses. But yes, if your sampling isn't high enough it won't look right anyway. That's why I suggest visible sample dots be superimposed on the sinc graph to avoid confusion.

[@ABaumstumpf]

The interpolation can be misleading, but the underlying problem is the scope, for what ever reason, not using the full buffer. Seriously - in most instances you just want to capture the data and view it. it would really make sense to set it so the sampling-rate over the capture-time pretty much fills the whole buffer - unless you specify the sampling-rate or other settings. And why the hell do scopes still have so little memory???? Make it 20$ extra for 4 GB RAM - at 32bit/point that would still be another 100 million sample points. i have seen explanations like "more sample points cause longer deadtimes" - why? The scope does not need to visualise all the points at once. The overhead of a simplified depiction is rather small, but the benefit of being able to store several times more data can be quit nice. For example when trying to capture the characteristics of many repeating analog signals - capture the first 2/4 signals, keep them stored in memory, capture the next, and the next, and the next.

[@juggernautforce]

Always trigger again after zooming in on a signal with the desired t/div.

[@richb313]

What you are also looking at is the artifact ridden excuse for poor Analog to Digital Conversion, especially in Music. It might be fun to do a side by side comparison of original Analog signal to Processed signal after conversion.

[@melkiorwiseman5234]

Interpolation: A fancy word for "Fill in the gaps." Extrapolation: A fancy word for "The rest follows the same pattern."

[@ratdude747]

Ah, aliasing. Trap for newbies when it comes to DSPs (which a DSO more or less is a graphical version of).

[@HighestRank]

Larry Bolan newbies, yeah I still get my head stuck in a wet paper bag, and I haven’t thought of dick and balls in 39 years.

[@The1wsx10]

the effective sample rate is making assumptions about the signal... the scope is a device to show you what the signal is. you have a scope that shows you what it assumes is happening, not a scope that shows you what is happening. you can only use the scope close to its sample rate if you already know what you are measuring.

[@TomatoBreadOrgasm]

Resolution, the only solution, the wise response to bad interpolation.

[@alphanimal]

The scope should show the dots on top of the interpolated curve when you zoom in far enough

[@tomvleeuwen]

I don't think you're quite on the mark when it comes down to the interpolated sample rate of the high end scopes. It means that they can vary the trigger delay by a few pico seconds and then overlay the different samples so that you actually have all samples measured, although on a different part of the waveform. This only works on pure repetitive signals where the trigger point is well defined.

[@autogolazzojr7950]

Pretty sure this is called equivalent time sampling (as opposed to to real time sampling). They used this a lot before high bandwidth adcs were cheap.

[@EEVblog]

That is Equivalent Time Sampling (ETS), quite a different thing to interpolation on a real time or captured signal

[@PplsChampion]

the mathematical motivation for using sinc is, if you integrate a square pulse, then integrate the resulting triangle, the integrate that, ad infinitum, you end up with sinc. it's analogous to going from "nearest neighbors" interpolation to "linear" to "polynomial" etc etc all the way to the "end"; so sinc is the "ideal" sampling kernel for interpolation in this way. it's also the fourier transform of a square unit pulse, i dunno if there's a more obvious explanation there.

[@LutzSchafer]

Absolutely, but the sinc isn't finite. Usually you get away with it if you have sufficient discrete samples so that the cumulative error is less than that of the instrument. Another option is to window your sinc with a Gaussian (as it will stay Gaussian in Fourier space ) which will make your interpolant finite.

[@PplsChampion]

@@LutzSchafer good catch thx

[@Matthias051]

Thank you

[@Robert_Wolf]

Nice video.. learnt a few things.. refreshed a few others.

[@superkristensen]

Great scope video, keep up the good work

[@warifaifai]

AWESOME. Haha its always nice to learn with you.

[@TheBypasser]

Cool, never actually seen it (in fact I use the linear interpolation all the time as it creates those visible slopes that tell you you are undersampling and should recapture).

[@johnyang799]

It can be mathematical proven from dac to adc both using sinc or same sample rate. I have done digital processing in university it can be proven. Nyquist theorem is also proven. But if it's from a unknown source, it's not the case. However, sinc is to utilize the available sample point in a most efficient way for lowest bandwidth. In a different perspective, if you use linear interpolation, you can creat high frequency noises which you don't want. Also you can post filter the linear interpolation result to get close to sinc. It's just digital filtering.

[@Audio_Simon]

Doesn't the scope tell you the bandwidth limit for clean interpolation at that memory depth? Or the effective sample rate at that memory depth / time base?

[@AlienRelics]

There should be no appreciable frequency content by the time you get to 1/2 the sample rate. Rule of thumb: -60dB down by that frequency. Any more causes aliasing.

[@ssks1979]

From one 10 year old to another, what else do you see? But back on subject, many parts of my old self just pines for a nice analog scope and signals below 100 kHz. Thanks for pointing out one of the digital scope traps!

[@theantipope4354]

In my case, I have an ancient 100MHz analog Tek scope. :)

[@nixxonnor]

This is a very interesting video about chasing red rabbits down narrow bandwidth holes

[@johnpenguin9188]

People get really confused about this with digital audio... It’s a lot of fun!

[@piotr86]

Wrong! It's not memory depth. It's lack of anti-aliasing filters for lower sample rates. Look at sample rate on 14:30 when you change time base (sec/div). Sample rate is automatically reduced as time base is increased, while acquisition is running. When you hit stop button, sample rate becomes frozen. Nyquist sampling criterion not met - distorted signal you get.

[@2oqp577]

Oh boy, oh boy. The Shannon Nyquist theorem specifies explicitly that you have to get a ratio of AT LEAST 2:1 of the HIGHEST frequency component of your signal. Else any anomalies at or above the 2:1 ratio in your signal is going to suffer representation with amplitude and phase errors. IMHO Shannon-Nyquist is a base to start from when designing requirements, but far from being the "rule". I actualy never use it as a base to start from. I look at the TDH I can afford and work from there. I am not belittleing the work of those two pioneers which I hold the highest regards but in college and universities, I think their work is misrepresented. I work in telecom.

[@TheActionBastard]

...I think I may be the only one who assumed dirty joke as a first thought. :\ sigh. This "growing up" thing is a lie. I keep getting older but never grow up.

[@WillArtie]

Yep, cock n ballz

[@KuraIthys]

No, I think you're not the only one. XD More like others are too polite to mention it. I was thinking this was unusually immature of Dave really. I mean, he's not the most serious person around, but drawing a dick is a particular kind of immature I wasn't expecting. XD

[@FarnhamJ07]

Naw, you definitely ain't the only one! I'm certain that most people had the same thought at first glance. Indeed, I'm pretty sure Dave had exactly that in mind when making the thumbnail. He mentions that the 10-year-old in him sees it too, and it would've been trivial to make an actual sin x/x curve to put in there. Instead, though, he drew it by hand, inaccurately, in bold, bright red. Silliness like that is part of what makes his videos so great, if ya ask me.

[@TheActionBastard]

To be fair I laughed hard as shit at it and pointed... no one but me is even in the room but I am laughing and pointing anyway. Dick jokes... still amuse decades later...

[@phoenixsmith4001]

This is why an analog scope is better ! If it says 200MHz is shows a 200MHz signal and something interpolated or GUESSED from a sample rate that should be at least 20 or more points per waveform, I think at least 50 points not 5 points ! And NEVER use any interpolation on a DSO.

[@ferrumignis]

Good luck catching that elusive glitch on an I2C/SPI frame using your analog scope. There ia nothing wrong with digital scopes provided you understand the limitations.

[@phoenixsmith4001]

@@ferrumignis Yeah probably not good for a glitch but I didn't say they were the only tool, just better when you get close to their bandwidth. Just try to look at a 90MHz digital other signal close to the bandwidth signal 100MHz DSO. Now setup an old tek 455 and use the variable holdoff and see a much better waveform than the 100MHz DSO will show for the same bandwidth rating. Like you said the limitations, and that's one of them, the biggest in my opinion.5 point per wave ? Even a square wave wouldn't show up good ! If they rated 100MHz DSO with a 100MHz sign wave showing at least 50 point, no interpolation. It would work great too. And analog are near instant screen update but yeah the newer scopes are getting closer if you have an extra $8000 or so to spare. Maybe less. And single shot.....I was thinking of using a tuner video recorder card with an analog to capture the signal in real time. If only I was lucky enough to get the DSO in Dave's recent giveaway ! Or that 13GHz scope Dave used, or the 30GHz scope. What are they using that high frequency anyway ? It must be military since the civilian world thinks 5GHz is the limit for CPU and motherboards. Intel, Motorola and Darpa have showed 1THz, yes 1000GHz chips ! The civilian world might be allowed to have them sometime in the year 5000 when we assimilate into the great hive mind. wiki HEMT transistors if you think I'm full of it, or Intel Terahertz, and see the references for both and the 1980s HEMT patents ! 1THz transistors !

[@ferrumignis]

@@phoenixsmith4001 No such thing as a 90MHz I2C signal, except for maybe some weak harmonics from the falling edges. Look at a 90MHz signal on an analog scope with 50MHz bandwidth and you aren't going to get a true representation of the signal anyway, though it will be better than undersampling on a DSO, which is why people need to understand their limitations. That said on a repetitive waveform the DSO would be superior again to the analogue if it had equivalent time sampling capabilities.

[@phoenixsmith4001]

@@ferrumignis Yeah, I couldn't remember the correct acronym and that's what came out in my brain. Still trying to remember. But you get the point. Like where Dave only shows 5 points per waveform or even 7 - 10 points it's not as useful. But an analog scope will still show the signal just with reduce amplitude from the bandwidth rolloff. Within reason. None of this 5 or 10 points per waveform crap where you can't even tell the waveform. Like the video points out. I'd say 50 points 20 or 30 minimum per wave. Feed this signal into a DSO and watch it cough up a furball, unless it is a very high sampling rate, and it will still probably fail due to the slower screen update. Jerobeam Fenderson - Planets or Jerobeam Fenderson - Shrooms Dave tried it in one video and even the high end DSO didn't come close to an old Tek scope. A mailbag episode I think ? I like an instant response, but DSOs are definitely better in many ways. Feed them an NTSC analog video too, and the DSO will be far to slow to respond. It still works but won't show the details like an analog would, with the phosphor instead of digital version so you can see screen motion all over the screen. At least all the scopes I've used. Never had a Lecroy or $100K scope. Maybe the $100K scopes can do it ?

[@stevewhite6252]

@JM Coulon Back in 1976 right after I graduated college, I built one of the original Altair 8800 computers from a kit which cost $400. I also bought the optional 4K byte memory card kit. After careful assembly, I turned on the computer and it didn't work. I probed around on the motherboard with my HP analog scope. When looking at the 2 MHz clock signal, it looked like a sine wave. I thought to myself "no wonder this thing doesn't work". I sent it back for repair. It came back working. The fix was to tack on a bypass capacitor to the memory card. Later, I got to thinking about how this computer could even work with a sine wave for a clock signal. It was then that I realized that I was looking at a 2 MHz square wave with a 500 KHz BW scope! The moral is that an analog scope can also give you garbage information if you don't use it properly.

[@nutsnproud6932]

Thank you Dave, I learned something today.

[@EEVblog]

Glad to hear!

[@mickstr5295]

Great information. Thank you.

[@manickn6819]

Wow I had one of those Tandy calculators in school. A real classic.

[@anonimuso]

Dave, you really should just open up a school for 'young players'. But you wouldn't have to really work hard. Just do a Guru type thing where you sit with your legs crossed and an oscilloscope in front of you. Then we can just come and go and ask you random engineering questions.

[@EEVblog]

I'll do my next live show cross-legged with incense burning.

[@vidasvv]

TNX 4 the upload

[@trampc9826]

It seems in signal measurement domain, sinc interpolation is the king and it is not possible for other types of interpolation to contend w/ it, such as spline, polynomial, etc. Is it still the case in 2023 when I'm commenting now?

[@philiplishman532]

Hi Dave, coincidentally I was snooping around the forum looking for some guidance on a sampling scope last night, so this is quite helpful - I'm trying to debug the ringing in an epaper boost circuit (I gather I need to design a snubber filter across the switch) but I'm using an old analogue 20Mhz oscilloscope, so measuring the frequency of the ringing is pretty tricky. I've just got to estimate it from the graticule by eye before it disappears - no cursors and no sampling! I don't know if you've done any vids about controlling or preventing ringing in boost circuits - one clue I've noticed that there is ringing is that when the circuit powers off there is a little (audible) noise from the circuit.

[@EEVblog]

Haven't covered that, sorry. You need a digital scope!

[@philiplishman532]

@@EEVblog Texas instruments and digikey both have guides on it with minimal maths needed, plus a little experimentation to find the right capacitance value. If I'd known how to design it to minimize ringing, I could have avoided the need for the snubber circuit altogether - as my reference circuit did. Digikey: www.digikey.com/en/articles/techzone/2014/aug/resistor-capacitor-rc-snubber-design-for-power-switches Texas Instruments: www.ti.com/lit/an/slva773/slva773.pdf Many thanks for the vids!

[@dorhocyn3]

Mind is blown, cool

[@kissingfrogs]

So why is the memory depth not always set to maximum?. What is the trade off?

[@ABaumstumpf]

This - exactly this. There is pretty much no tradeoff. And it should be the default-setting.

[@autogolazzojr7950]

Basically everything runs slower : math functions, refresh rate, etc

[@ABaumstumpf]

@@autogolazzojr7950 ... only if they were braindead and would brute-force everything. There is no need to perform maths-functions on the full raw data you know? You can just apply them to a sampled set or other subsets and get pretty much no performance downsides - and then if you choose you could apply them to the whole dataset and get more accurate results when needed. But i am sure that to you a car having a bigger trunk also means you will always take longer to load and unload it, even if you just take out the last part you put it.........

[@pepe6666]

yuck :( i kinda wish that the display just said in red the smoothie line and showed the dots in a different colour. that would be great cos then you can see for yourself the interoperation plus the data points.

[@tapravdec]

It's a trap, if you don' track sample rate. You can clearly see the sample rate was throttled down to 2.5Msa/sec @ 50ms.

[@fzigunov]

Also called Aliasing.

[@What_I_Make]

Basically, I basically want to basically try not to say basically.

[@8bitbubsy]

You basically failed...

[@R2D2internet]

You got the persistence in "Infinite" 4:05, there was no bug in 3:45 ...

[@saltrocklamp199]

Why don't they add a bigger dot where the actual data points are located, so you can see both the real and interpolated data on the same panel?

[@EEVblog]

Might be a handy option

[@REALIVH]

Splines or b splines math used in vector curve, an analog does not that.

[@RinksRides]

7:29 - It's Retrowave, Dave. B-) Good to know! I have that exact scope, much faster now, just updated to latest firmware.

[@God-CDXX]

my Oscilloscope is jealous of your Oscilloscope

[@BlackEpyon]

I've got an analogue 20MHz scope that's older than I am. It does what I need it to, but one day, I'd like to get a digital one.

[@GoldSrc_]

I only have an old Kenwood 20MHz scope lol. It saved my ass from doing trial and error trying to fix an old CD player. Also, demos like Oscillofun look better on analog scopes.

[@BlackEpyon]

@@GoldSrc_ Now I know why we lost Black Mesa, lol. Stupid budget cuts.

[@tomw7751]

Dave, if you don't meet the Nyquist criteria, and suffer from aliasing/folding, you're really not entitled to try to make any sense out of what you see on the scope. Screwed is screwed. There's no sensible interpretation of undersampled/aliased signals. Other presentations - dots, linear interpolation - are all equally useless if your data are under sampled. There's no good way to look at aliased data; it's ruined, crap.

[@HighestRank]

12:36 talking about rolloff, what’s up with the guppy fish gurgling audio?

[@EEVblog]

Strange, not sure what that is.

[@needforsuv]

Alternatively, go in as much detail as you need. If you don't need 5000 'packets' just sample 1 or a few. Or maybe 10

[@secallservice1394]

If I interpolate my bank account balance, at the moment I got 1,600€! That's how I became an interpolation aficionado

[@EEVblog]

Interpolation in the banking world is called fractional reserve banking.

[@Zenodilodon]

1:30, oh look it's the BROADCOM logo :)

[@DAVIDGREGORYKERR]

Does that scope not have a Kaiser Window function?

[@ytrewq6789]

Everybody on YT seems to haft to try putting that in there thumbnail at some point?, but i'm more used to seeing it with teen vloggers rather then hear? LOL!

[@DrakkarCalethiel]

Confusor, AvE must have infected you. :D

[@Eo_Tunun]

Wait for the next time AvE turns some harbour freight tool upside down, then discuss how all the electrons are falling out… ^^) Next step will be identifying the magic smoke as "The Schmoo (©)"

[@denny9931]

@@Eo_Tunun Pixies and Schmoo!

[@Eo_Tunun]

@@denny9931 Wait for the Cockford-Ollie multimetres! :oD

[@williamsquires3070]

The angle of the dangle = (square root of the (ventilation) holes in the back of the scope) x (the mains frequency) x (the memory depth in bits) all over pi! 🤪 Yeah, right.

[@EvelienSnel]

I found the SIN(X)/X setting on my DS1054Z. It says it is "ON", but it is also grayed out. Pushing the button next to it does not change it to "OFF". I must be doing something wrong, but what?

[@larrypriest5789]

my brain has not hurt this much since college

[@EEVblog]

Sorry!

[@larrypriest5789]

it's alright - needed to knock some calcium around anyway.

[@scotchrobbins]

Is the interpolation in place to beat aliasing?

[@yoramstein]

In my country we say "from so many trees the forest can not be seen"

[@BoydWaters]

Yes, USA English, a common phrase is "Can't see the forest for the trees". Which is when you focus on so much detail, you cannot see the overall shape. Aliasing problem is maybe the inverse of that: the shape you see is not real. :-)

[@yoramstein]

@@BoydWaters I ment spreading the max sampling points over long time of recording comes on the account of sharpness (resolution) of one cycle (the forest is one cycle the trees are the long time)