Guest Video - Karl Adams - Audio Distortion Measurement

In this guest video Karl Adams shows us how to measure low levels of distortion in audio circuits. The example used is an LM1875 in a compound configuration.
Subscribe to / keicar67
Forum: www.eevblog.com/forum/blog/gue...
EEVblog Main Web Site: www.eevblog.com
The 2nd EEVblog Channel: / eevblog2
Support the EEVblog through Patreon!
/ eevblog
Donate With Bitcoin & Other Crypto Currencies!
www.eevblog.com/crypto-currency/
EEVblog Amazon Store (Dave gets a cut):
astore.amazon.com/eevblogstore-20
T-Shirts: teespring.com/stores/eevblog
💗 Likecoin - Coins for Likes: likecoin.pro/@eevblog/dil9/hcq3

[@7head7metal7]

why didn‘t I know of this man before? Exactly my interest, directly subscribed!

[@rpbale]

Ditto

[@OpenTechLab]

Silky smooth audio. Much better than mine!

[@ChongMcBong]

yours was pretty good too :)

[@ElmerFuddGun]

OpenTechLab - Your audio was quite good although IIRC it was a bit louder here and there where I think you were closer to the mic or using a different one. Perhaps a bit over modulated at times. Karl's audio is good but often he was quiet and almost mumbling. I'm sure you both will improve over time.

[@allthegearnoidea6752]

Yes his audio is good better than. Good audio is hard.

[@flymypg]

Well done! I love seeing lab "tricks" that combine the realities of instrument limitations with the desire to measure at or near the noise floor. Measuring extraordinarily low components of voltages in the audio band is relatively straightforward compared to doing the same for currents, which I did as part of my technician day job while attending uni, where I was working with femtoamps. So I was a bit surprised to not see coax signal leads used everywhere possible. The bane of my existence was fluorescent lighting noise and powerline harmonics making their way into my test setups. (BTW, this is still a problem today with LED lighting: I have a friend who makes a tidy living making shielded LED lighting for places like FCC compliance testing labs, radio telescopes, and spy agencies. The number of "tricks" he combines into his system are astounding.) I'd always first test the "0 dB amplifier" (a piece of wire) before the DUT, to ensure all my noise sources were either removed, or at least characterized. I've been a software person for the past few decades, specializing in instrumentation and control systems in general (sensors and actuators), and signal processing in particular. My analog lab experience provides endless joy when I need to take EEs to task for making my work unnecessarily difficult ("Oh, we'll fix that in software."). But that's mainly said in jest. I really like working with EEs because they truly understand noise, both as signals and as statistics, which relatively few software folks adequately appreciate.

[@johnfrancisdoe1563]

BobC He did test the 0dB amp first. In fact he ended the video before plugging in the DUT !

[@flymypg]

Yes! I had brain-flipped the signal source for the amp. Hate when that happens.

[@KerryWongBlog]

Thanks for the wonderful video!

[@BrunoPOWEEER]

I'm a former audio professional... Inreally enjoying watching you playing around with your tools. I just love all this science and old school electronics!! SUBSCRIBED to you channel mate... ohh yeaahhh =]

[@AmRadPodcast]

Your 62a is in much better shape than mine! Thanks for the video. I'll have to try this out!

[@AdmiralQuality]

Thanks Karl! *Followed!*

[@TheBrightPixel]

Oh yeah. This is right up my alley. Nice one!

[@maxheadrom3088]

My kind of story!

[@rpbale]

Love it. This is my kind of guest video. I've got one of those HP spectrum analyzers. Can't wait to try this approach for low level distortion measurements.

[@zx8401ztv]

Thanks karl, i have a better understanding of the distortion meter, notch filtering then boosting what you have left to measure it. A million years ago i made a function generator, to get the best sinewave i used a twin T filter and outputted it to an oscilliscope, a rough method i know.

[@rachidajewher8649]

if the sinewave signal thd+n exeed the thd+n of the DUT (an audio ADC) do you still can calibrate let say a reference level of +4dbu (analog) =18dbfs (digital) , my small finger tell me that i need to match the dynamic range of the sinewave with the DUT correct me if i'm wrong

[@g0hjq]

Interesting demo of distortion measurements, I learned a lot. Thank you Karl.

[@csvscs]

Thank you Dave for introducing a new channel.... Especially one for audio nerds like me

[@Justsquareenough]

Thanks Karl.i appreciate the work that went into this. Well explained. I've subscribed

[@Petertronic]

Excellent video, loving that test gear.

[@TheGFS]

Good job Dave .. You get extra points for this.. Both guest videos have been great and so much better than having no videos (as most youtubbers would do) so using your "downtime" to introduce these guys and specially letting them put up videos , again.. Good job :)

[@itsonlyaudio]

Very cleverly done Karl. This architecture is exactly the one used by Audio Precision on their flagship analyzer APX555. They achieve 120 dB after 30 years, you get to 106 - I call that a score and a half. Definitely subscribing to your channel.

[@sheepslinky]

Very nice to watch someone demonstrating practical, attainable, low noise audio electronics. I also use this technique, except via Krohn-Hite filters as notch filters. A good filter is extremely useful, even with digital techniques, and I often keep my filters in front of my scope and other measurement equipment. Excellent job, though, I'm sure many audio nuts will learn a lot from this.

[@BMRStudio]

Excellent guests! Thanks Dave!

[@Gouwomb]

Thank you Karl Adams, I found it very educational.

[@JohnAudioTech]

Interesting stuff! Hope to see the results of the LM1875 amp project.

[@diabolicalartificer]

Thanks Karl, I have similar gear to yourself so this is a pertinent, very interesting video.

[@sokolum]

Enjoying this format!

[@KerseyKyle]

The picture quality of this video is very clear, good job.

[@tomwimmenhove4652]

Amazing. I was researching techniques for measuring ultra low THD just the other day!

[@michaelhawthorne8696]

"The harmonics are down here in the grass." LMAO, nice turn of phrase, not heard that one before. Nice video will subscribe

[@duroxkilo]

indeed, cheers!

[@ottersdangerden]

I like larger channels helping out small ones, especially when they have good content. Yesterdays vid on fpga was pretty interesting, though I was already subscribed to em. This one eh, maybe. In the 3d printing world Joel Telling did the same thing and was pretty nice and I found some more things to watch which is always a good thing.

[@springrollwang4441]

Finally Dave is brave enough put audio electronics video on his channel. Love it.

[@FindLiberty]

very nice presentation

[@davidwillian2279]

awsome content, Karl! Subscribed.

[@robertfenney]

excellent!

[@glynnhm0lsg308]

As a ham this is more up my street than yesterdays vid

[@Aneurysm06]

you should have a radio show,so smooth , subscribed

[@JackZimmermann]

Yup, that ultra low distortion generator is amazing! Had to build a Twin-T notch filter when building my headphone amplifier to be able to measure THD with the QuantAsylum QA401. Measured -114 dB THD with a 32 Ω load. Can you hear the difference? I don't care! It's trying to do the best you can that's important. Yeah, I know, electronics nerds who like to mess with audio are automatically audiophools.

[@johnfrancisdoe1563]

Jack Zimmermann Not really. Actual audiophools will buy products that make no difference even with such extreme measurements. Stuff like low distortion mains cables that (at best) increase the amount of mains harmonics reaching the amplifier.

[@JackZimmermann]

Yeah, there are some crazy shit in the audiophile circles. Fortunately there are some level headed (and very knowledgeable) engineers, like Douglas Self and nwavguy.

[@RobertKohut]

Nice!!

[@johnpossum556]

Did anybody else find the irony in this low THD vid having so much fan noise in it? But it does harken back to interesting times. Good video!

[@MarcelOoms]

What a great video! Would very much like to build that amp! Will there be a pcb out? Have some LM1875s and LM3562 lying around. I guess the layout is critical, though.

[@jpalm32]

Good variation of electronic disciplines

[@myradiovideos]

Just took delivery of a Leader LDM-170.. Needs some TLC on the dirty switches, but the unit is working. Your video helps me better understand its capabilities.. Thanks for doing this and explaining more of how to look at very deep signals... Robert

[@quakesin1982]

Thanks for sharing Dave...err Karl!

[@bblod4896]

Cool demo. Of course, owning such equipment is another thing.

[@error079]

a big fail of the "algorithm'" not to have show me your channel before. subed!

[@FatedSnowfox]

Never seen your vids before, but loved this one! I bet you’d be awesome with Dougie Ford too

[@SoddingaboutSi]

Yay an 8562a! Very interesting. I see your CRT is as dim as mine lol.

[@Dave_____]

There are LCD replacement kits out there for the 8562a

[@LasseHuhtala]

Good on ya Karl, so far you've gotten a boost of ca. 600 subscribers. :-)

[@allesklarklaus147]

nice video, I liked it

[@gunderconk]

Nice! Thank you

[@Matt-fl5mv]

I would like to have been tought what harmonics means and what distortions actually are...

[@inductorbackemf7204]

Fun video good job friend stay safe,hope your channel does very well!

[@timmgiles]

Really interesting video Karl and well put together - not really my day to day interest but best of luck.

[@fuuturist]

great video, thanks Karl! why so many dislikes? :(

[@antoineroquentin2297]

solar roadway manufacturers forgot to turn their votebots off.

[@volvo09]

Probably people who really aren't into electronics but just like Dave videos. The topic was over my head, but I will still learn from it, so Thumbs up. I love learning new channels I wouldn't have otherwise found!

[@florincristian7904]

This read and DB SINAD ? Thanks

[@dxhighendamplifiers]

I use to do the same..this is my thing too..i am Destroyer x from diyaudio

[@patricksmith4424]

I can't believe that more modern multimeters don't have THD measuring facility on them. This can't cost that much to add to a meter. The only one that does this is the Keithley 2015/16 and they cost around 7000 dollars new.

[@esdblog6100]

Good video. Are your sure that those -105dB (~5uV) distortion is really distortion and not pick up form other sources?

[@nerdacs]

Can I use this to measure my fuzz pedal?

[@andrijaifkovic7066]

That oscillator you are using has harmonic distortion at the order of -140dB or more. Impossible to measure its own distortion without notch filters and even then...

[@zaxmaxlax]

Is he using shielded unidirectional power cables lubricated with snake oil to make those mesurements?

[@bryandrap123]

Actually it was gold plated fiber optics

[@Thefreakyfreek]

Bryan Draper you know that the Belgians had wirles communication at least 2000 jears ago that startet diging and no wires were found

[@Audio_Simon]

Great vijayo! BUT why make this effort when you can buy an audio interface for the PC with about -110dB THD+N and run all the measurments you want?

[@twin1q]

A few thoughts. 1) Did you verify your distortion of your source? if so, what was it? 2) You will have FFT leakage if your source is not coherent to the analyzer. 3) You can verify your setup by using a Stanford Research System SR1. It has a rating of better than -110 dB THD.

[@user-xk7qb3ek2l]

我来听天书了！！！哈哈

[@samchan5251]

I am lost in the -80dB ...

[@travisbates340]

Obligatory subscription..

[@JLSoftware]

Define distortion. What is the relationship between distortion and harmonics? Explain the significance of 80 dB. If that 1kHz is such a clean signal, why all the noise at the bottom?

[@johnfrancisdoe1563]

JL Software Distortion is the (unwanted) deviation between input and output signal shape. Harmonics are the occurrence of integral multiples of the desired pure frequency. For analog equipment, waveform theory says all the distortion will appear as extra harmonics (harmonic distortion). Also, in audio applications, we only care about the part of the signal that can be detected by human ears. Thus measuring only the increase in harmonics below 20kHz is more relevant than including any distortion above that range. Furthermore if the device under test isn't unusually bad, looking at just the first few harmonics will cover almost all the actual distortion, thus allowing him to set his spectrum analyzer to not look above 5.1 kHz in this test.

[@alexdavis9794]

Distortion is something that adds harmonic content to your incoming signal. So if you feed in a pure sinusoid at a given frequency f, called the fundamental, you'd see distortion as added tones at multiples of that fundamental frequency. In fact, multiples of that fundamental frequency are, by definition, harmonics. This doesn't include noise, which is not related to the frequency of the incoming signal. As to why 80dB is important, if your test equipment only has 80dB of dynamic range, you can only detect signals 80dB smaller than your highest input level. If your fundamental was scaled to hit your highest level, you could only see a harmonic 80dB lower than that. A good, low distortion audio amplifier might have a THD spec of -100dB, which actually sets the level of its highest harmonic even lower than that, since THD looks at the sum of ALL the harmonics! The final element of all of this is noise. Your test equipment itself, no matter how good, will have what's called a noise floor - a minimum level beyond which you can't distinguish the signal you want to measure from the noise inherent in the system. In order to make a good measurement , you need to ensure that the signal you want to measure sits far enough above the noise floor of your test equipment that you're actually measuring it, rather than just measuring the noise in the system.

[@JLSoftware]

Thanks a bunch!

[@JLSoftware]

Much appreciated!

[@Petertronic]

The scale of the analyser is logarithmic, the sensitivity goes up in orders of magnitude towards the bottom of the display, to show the biggest dynamic range clearly

[@garydavies6370]

alternatively, have a precision amplifier at the same gain as the audio amplifier unloaded, then connect the loudspeaker load and measure the difference between audio amplifier output and precision amplifier output, = THD + noise + DC offset

[@codebeat4192]

I like to see a device that you can make yourself to include into projects. This could be nice for auto maximum volume without clipping, distortion.

[@dxhighendamplifiers]

I am using audacity, sinusoidal generation and them exported to wave.... result is the same.... output comes from notebook

[@6Diego1Diego9]

Who the fuck is Karl?

[@michaelevans6456]

I mean - okay. sure.

[@splitzzzzz]

Great video but shooda cleaned his fingernails! ;-)

[@klaper10]

i like it because of engineering / measurement point ;) i dont give an f about audio voodoo stuff;)

[@seancastledine8983]

Wake me up... before you go go.

[@bbreeuwer4577]

Jeeze, this is really measuring distortion like we did when we used to live in caves. Nowadays, just get a decent (USB) sound card which goes MUCH quicker and you can easily measure down to 0.0005-0.001% or even lower. For around $400-500 there are even more professional solutions to go down to 0.0001% or lower.

[@johnfrancisdoe1563]

B Breeuwer Really? That would be a card with a lot of ADC bits to actually measure such low amounts of distortion directly. But even then, his technique would also work to measure distortion lower than the input resolution of a sound card.

[@diabolicalartificer]

"you can easily measure down to 0.0005-0.001% or even lower." How, with what? If your on a low budget there is no software or gear (that I know of) that can measure that low a distortion, that's why Karl and other's like myself pick up old distortion meters and SA's.

[@allesklarklaus147]

Old test gear is cool. like he said in the beginning of the video. Who gives a crap about a PC with a soundcard in it

[@bbreeuwer4577]

Diabolical Artificer. A lot of 24 bit sound cards can go that low. As for software there are multiple flavours but ARTA is what I use.

[@bbreeuwer4577]

alles klar klaus. If someone is that serious about getting such low THD+N figures he should care. But basically my budget cares. The gear he is using, even bought second hand, is a lot more expensive. Also in the end it's much more hassle, which means that the results will be less accurate and less consistent. In my opinion he should at least show the alternatives.

[@Sixta16]

Why bothering using such obsolete equipment to measure the distortion, if one can use his own 24bit PC sound card in a loopback mode? Of course the better the soundcard, the better the measurement precision.

[@techmage89]

Sixta16 Where on Earth do you find a PC sound card that isn't horrifically noisy? They're convenient, sure, but precision instruments they're not.

[@antigen4]

i think the big irony is that distortion measurements are made with 'test' or pilot tones (sine waves) rather than actual music that has real transients etc ... yet another way i guess audio specs are out of touch with reality and why there really isn't much correspondence between specs and what one hears

[@bertvisser6423]

Fell asleep 5 minutes in.

[@bertvisser6423]

Yes,you just made one,congrats! You're a keyboard warrior now,tell me,you must feel proud and accomplished now right?

[@justintimber5058]

For me it seems, that Karl doesn't know his instrument (LEADER) very well. And for the EEVblog channel it is not a good way to support channels like this.

[@johnfrancisdoe1563]

Justin Timber What did he miss?

[@mosfet500]

Here's the problem Karl. No one on the planet can hear the difference between 0.1% and 0.01% distortion, much less 0.001%, in fact once you get below about 0.5% distortion it is basically a non-issue. No one can hear it in a double blind test. Audio critics are the worst, by the way. Stereophile magazine's Michael Fremer was famous for getting all goose bumpy about an amp with around 20% distortion before someone pointed out it had 20% distortion! What's worse is we like distortion, just special types, ask any guitar guy or tube guy. I love just the right amount of second harmonic tube distortion personally. Somewhere in the nebulous mess of audio nonsense someone figured distortion was important, of course it was 5 and 10% distortion in those days! So manufacturers latched onto distortion like it actually meant something and their data sheets kept competing with each other for who could have the lowest distortion figures. Unfortunately no one has shown that super low distortion has anything whatsoever to do with musicality!

[@tommihommi1]

mosfet500 in a professional toolchain, you want to keep unknown distortion down in every single step. You can always add wanted distortion later

[@EEVblog]

In the seismic industry I was in, every 0.001% distortion mattered *a lot*. For audio, distortion still matters because you can have many chains in a system and they add up, e.g. a complex mixing console.

[@magnehaneberg8605]

That's right. If you're running with analog mixing consoles, the distortion needs to be right down at minimum. Extremely important if you're building any serious piece of equipment!

[@andrijaifkovic7066]

Actually, I feel it doesn't really matter whether you can hear 0.1% and below or not (I do think I've seen references that you actually can down to 0.0x% or something). I instead consider it a challenge when I work on audio. Is it measurable? Yes? Then why not minimize it, if for nothing else than for intellectual challenge? Also, you never know when being able to measure this comes in handy - for example I found that I had a badly designed voltage regulator on a DAC chip (not really regulating well due to bad bypass capacitor choice) from seeing unusually large distortion on measurement; harmonics around -80dB that you would dismiss as non audible but which exposed a design flaw.

[@fearlabsaudio7815]

In a professional mixing environment, I agree that below 0.01% it really does become mostly a non-issue, unless you are chaining a lot of devices together. Even 5% THD isn't honestly that noticeable to most people. However I can wager than an experienced sound tech, in a familiar setting, can experience a noticeable difference between 0.1 and 0.01 in the playback chain, enough to compromise the mix of a song. The coloration that imparts on the music can become relied upon and once the mix is played back elsewhere, that coloration is gone, making the mix no longer "sit right". It all gets pretty subjective at that point as to what really matters though.

[@delta-game]

lots of 'umm' distortion sneaking in

[@ITTom]

not my kind of story....

[@xartpant]

Guest videos is not a good sign for the future of this channel.

[@kiwifrogg]

Dave has gone on holiday, there will be 12 guest videos while he's away....he is helping small channels at the same time.

[@sparkplug1018]

Dave is on vacation, and filling the dead air with some guest videos, to help other channels get exposure.

[@SoftBreadSoftware]

I think it's cool of Dave to give other youtubers/engineers exposure even if it's not general electronics engineering but this more niche stuff. Obviously by the rest of the comments and ratings I'm not the only one.

[@wowfubar]

Get a life!

[@alimmi9]

xartpant you didn't get why he's doing this segment

[@12345678901234567432]

Nc video but quit smoking