• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

How audible is distortion?

oivavoi

Major Contributor
Forum Donor
Joined
Jan 12, 2017
Messages
1,721
Likes
1,934
Location
Oslo, Norway
I am usually careful to use "overtones" and "timbre" rather than "harmonic series" to describe the sound of musical instruments. Many of them have non-harmonic components, including brass and most wind instruments. Strings can generate beats among the actual strings on the instrument as they are played, etc. Drums are impulse generators and yet do have fundamental'ish terms depending upon how the head is tuned. Piano is tough for many reasons: the percussives when hammers strike strings, there are 2-3 strings per note and those strings are tuned to sound "richer" so are not necessarily exactly the same note, different strings (different material/construction) have slightly different sounds, the sound comes from strings and sound board, the sound can vary along the string since there are nodes and antinodes, and of course that also affects how nearby strings interact, the sound is modified by interaction of the sound waves from various strings within the piano and sound board depending upon the position of the lid, octaves are generally (intentionally) "stretched" at the top and bottom, it is a very wide frequency range to cover, etc. etc. etc.

I made some files years ago with added distortion for people to try. IMD is much easier to hear than THD, but in music any distortion is harder to hear. The rule of tens is not quite right but decades ago I was curious and did some blind tests with friends and customers of the store and it was not too far off. That is, for a pure (single) tone in the midrange or vocal band folk could detect down to about 0.1% distortion with moderately high volume; with a few multiple tones more like 1% depending on how they were spaced, and for musical selections or many tones more like 5% - 10%. Music includes so many harmonic and non-harmonic frequencies anyway that telling what is distortion can be hard until it gets pretty high. And then add the whole loudness curve bit and any general comments about "x% distortion is audible" pretty much fly out the window.

IMO - Don

Interesting comment, Don. Thanks! My question would be whether this kind of blind testing is comparable to ordinary listening. I mean, it seems fully reasonable to me that 5 to 10 percent distortion (not uncommon in speakers) will be undetectable for a lot of people when hearing certain musical pieces. As you say, how does one know what is distortion and what is not? I would nevertheless assume that over time, with prolonged listening, the non-distorting system will sound better on a larger variety of material - solo voices, choir, solo piano, etc. These small segments where the distortion becomes noticeable might then increase the sense of artificiality of the system as a whole. So I still think best practice in audio engineering is to strive for speakers and components with as low distortion as possible.
 

Cosmik

Major Contributor
Joined
Apr 24, 2016
Messages
3,075
Likes
2,180
Location
UK
Benchmark recently published an interesting write-up on distortion: https://benchmarkmedia.com/blogs/application_notes/interpreting-thd-measurements-think-db-not-percent?utm_source=Benchmark's+Application+Notes&utm_campaign=f9856e624b-EMAIL_app+note+11-20-17&utm_medium=email&utm_term=0_7c8c792ee5-f9856e624b-194245873

One of the points that were striking to me, was their point on reproducing the sound of pianos. It is often assumed that solo piano is one of the most difficult things to get "right" for a sound reproduction system. I tend to agree with that. According to Benchmark's John Siau, this might be the explanation:



I would perhaps be inclined to think that distortion in the speakers is a more likely culprit than distortion in the electronics. But then again, who knows.

---------
Btw, a fellow over at Diyaudio has created a really useful blind test on non-linear distortion: http://www.diyaudio.com/forums/everything-else/314218-test-ears-abx-test-44.html#post5242441
I've never thought that piano was difficult to reproduce, but maybe I wasn't listening hard enough for that effect. Presumably there are plenty of recordings from the past that have a modicum of distortion. Perhaps it could be interesting to try to find some examples. Or to deliberately add distortion to exemplary modern recordings..? Or even to make some recordings with your piano - ours is a bit out of tune...

Edit: Sorry, it was John Siau who has the piano...
 
Last edited:

svart-hvitt

Major Contributor
Joined
Aug 31, 2017
Messages
2,375
Likes
1,253
Benchmark recently published an interesting write-up on distortion: https://benchmarkmedia.com/blogs/application_notes/interpreting-thd-measurements-think-db-not-percent?utm_source=Benchmark's+Application+Notes&utm_campaign=f9856e624b-EMAIL_app+note+11-20-17&utm_medium=email&utm_term=0_7c8c792ee5-f9856e624b-194245873

One of the points that were striking to me, was their point on reproducing the sound of pianos. It is often assumed that solo piano is one of the most difficult things to get "right" for a sound reproduction system. I tend to agree with that. According to Benchmark's John Siau, this might be the explanation:



I would perhaps be inclined to think that distortion in the speakers is a more likely culprit than distortion in the electronics. But then again, who knows.

---------
Btw, a fellow over at Diyaudio has created a really useful blind test on non-linear distortion: http://www.diyaudio.com/forums/everything-else/314218-test-ears-abx-test-44.html#post5242441

You wrote:

«I would perhaps be inclined to think that distortion in the speakers is a more likely culprit than distortion in the electronics. But then again, who knows».

Benchmark sell electronics, not speakers. If you tell me the incentives, I can tell you the outcome ;)

Other than that, I agree the Benchmark paper is a good read.
 

DonH56

Master Contributor
Technical Expert
Forum Donor
Joined
Mar 15, 2016
Messages
7,835
Likes
16,497
Location
Monument, CO
@oivavoi -- Some of the testing was with musical selections. As you might expect the detectable level of distortion depends upon the music. Back then I used AB to see when people could detect the difference (didn't have an ABX device at the time IIRC) and added distortion until people could tell. It was not a perfect test as I had to change the distortion and then level-match again so we'd do a test run, change conditions, and repeat the run. And of course the type of distortion mattered; mostly even, mostly odd, or a mixture of both. Sometimes they picked the more distorted version as "better" but I was mostly interested in when they could tell a difference. And in the bass region people would often prefer the runs with higher distortion as it was easier to hear and folk thought the sound "fuller" and "richer". I suspect the level of detectable distortion would somewhat mirror the loudness curves, and in fact that was one of my goals at the time, but I do not have my notes anymore. I am sure folk like JJ have much more to contribute on the subject. For me, I think it is very complex and saying "x% distortion is bad" without context is not real meaningful unless "x" is very large.

@Cosmik -- Piano is actually somewhat a pain to record and that gets reflected in the recordings. From "out front" it's not that much harder to record than anything else IMO, but many (myself included) like to be in the pianist's seat when listening to a recording and then it gets harder to decide what and where to mic the thing. Similar concept applies to drum kits; people like recordings to sound like they are on the throne, or sitting in front of the kick drum, so the kit ends up close-mic'd with a bunch of different mics to capture every little thing. IME/IMO attending the live show often sounds less "there" than listening to the recording. One reason I feel debating live vs. reproduced sound is somewhat pointless; they are, well, different.

My 0.000001 cent (microcent) - Don
 

Fitzcaraldo215

Major Contributor
Joined
Mar 4, 2016
Messages
1,440
Likes
632
I don't think that the difficulties with piano reproduction are purely ones of playback frequency response and distortion. I think often there are problems at the recording end, too often from just miking too closely.

The sheer size of the piano and its broad frequency spectrum present some unique recording and reproduction problems compared to other instruments. And, close miking can distort spatial properties that we hear from the audience perspective if not carefully mixed. Also, what the mike hears up close can present a different tonal balance. A piano heard from one foot away sounds different from 50 or more feet away in the hall, although mikes at 50 feet would not work either for a variety of reasons. There may be more apparent detail close up, but some of that detail is not heard by the audience with the same emphasis. And, often close miking gives more emphasis of higher frequencies or of Glenn Gould's famous humming to Bach. Recordings usually try to tame this, but with varying success.

Much of this is also true of other instruments, but to a lesser extent. It seems as they are closer to point sources than a piano. Nontheless, standing next to a violinist does not yield exactly the same sounds tonally and spatially as further away. There are also minor, extraneous bowing noises heard close in that an audience likely does not hear.

I don't think modern playback systems of quality have much problem with low distortion, tonally accurate and dynamic piano reproduction. The problems at the recording end are much more difficult to get right.
 

tomelex

Addicted to Fun and Learning
Forum Donor
Joined
Feb 29, 2016
Messages
990
Likes
572
Location
So called Midwest, USA
A long time ago I came across a schematic using a particular tube that had even and odd curvatures depending on biasing. So I slapped together the circuit, and from the neutral output, if I went too far second harmonic is literally sounded syrupy, if I went too far odd harmonic it sounded harsh and shrill. A little either way, odd or even directions produced nice affects, (even giving a little bit of lushness, and odd giving a little bit of bite), and I could live with either one. This was with music. I can also say that I would not be able to tell if I did not know which way I went as far as if someone did the adjustment I could say, hey, someone added my distortion circuit, unless you went to the extremes. Pretty much that's why I take recordings as they come focusing more on clarity and dynamics but above all I have to like the dang music first or fooorggeeeteiiiit.
 

fas42

Major Contributor
Joined
Mar 21, 2016
Messages
2,818
Likes
191
Location
Australia
I do.

I have Altec 416Bs in 13.75 Cu.ft.(net) enclosures(32Hz tuned) for comparison with my 'little guys'. However, maybe that effect is why I don't add a sub-woofer? No, lack of space for another large cab is why. I like large cabs. and high efficiency drivers.
I had the most clear "evidence" for the relative importance of the deep bass fairly recently - for my listening ears at least. Most systems with meaty subwoofers sound a bit ridiculous to me - just a more sophisticated version of what kids have with massive bass drivers in their cars - it's all about moving huge amounts of air, and very little to do with music ... but an audio system up the road has hugely heavy, sealed subwoofers, EQ'd with DEQX, with super clean bass note reproduction - a frequency sweep down to the lowest, and back up again was notable for the fact that all one heard was the fundamental, at all times.

Yet, put on my organ "showoff" CD, and the rig wimped out - the presentation was a mere shadow of what it should have been - the grandeur, and richness was well and truly missing.
 

fas42

Major Contributor
Joined
Mar 21, 2016
Messages
2,818
Likes
191
Location
Australia
I've never thought that piano was difficult to reproduce, but maybe I wasn't listening hard enough for that effect. Presumably there are plenty of recordings from the past that have a modicum of distortion. Perhaps it could be interesting to try to find some examples. Or to deliberately add distortion to exemplary modern recordings..? Or even to make some recordings with your piano - ours is a bit out of tune...
I agree ... piano is quite straightforward, once the key aspects of the playback chain are in place. Having a rig handling the range from subtle meanderings to full blown, crashing chords is a good, easy test to try.
 

Wombat

Master Contributor
Joined
Nov 5, 2017
Messages
6,722
Likes
6,459
Location
Australia
A long time ago I came across a schematic using a particular tube that had even and odd curvatures depending on biasing. So I slapped together the circuit, and from the neutral output, if I went too far second harmonic is literally sounded syrupy, if I went too far odd harmonic it sounded harsh and shrill. A little either way, odd or even directions produced nice affects, (even giving a little bit of lushness, and odd giving a little bit of bite), and I could live with either one. This was with music. I can also say that I would not be able to tell if I did not know which way I went as far as if someone did the adjustment I could say, hey, someone added my distortion circuit, unless you went to the extremes. Pretty much that's why I take recordings as they come focusing more on clarity and dynamics but above all I have to like the dang music first or fooorggeeeteiiiit.

That sounds interesting. Can you find the schematic and post it?

It could may be a useful effect with a 'clean' tube guitar amp - I am only interested in constructing tube amps for guitars.
 

tomelex

Addicted to Fun and Learning
Forum Donor
Joined
Feb 29, 2016
Messages
990
Likes
572
Location
So called Midwest, USA
That sounds interesting. Can you find the schematic and post it?

It could may be a useful effect with a 'clean' tube guitar amp - I am only interested in constructing tube amps for guitars.


I have looked for it over the years, it was on paper only, no luck. Anyway, nowadays you would go a digital device or software program to do the same thing.
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,198
Likes
16,981
Location
Riverview FL
Benchmark sell electronics, not speakers.

They dabbled, but apparently have discontinued that activity.

https://benchmarkmedia.com/collections/speakers

I would perhaps be inclined to think that distortion in the speakers is a more likely culprit than distortion in the electronics. But then again, who knows.

Speakers here have far more measurable distortion than the electronics. Distortion in my speakers:

Is inaudible and unmeasureable (with my noisy tools) at low volumes.

Once the harmonics rise above the noise floor, the distortion products can rise more rapidly than the fundamental level.

The little JBLs have more distortion (at a given SPL) than the MartinLogan panels.

The MartinLogans comfortably play more loudly than the little JBLs, and are the "go to" for serious listening. The JBLs are my daily drivers now for casual/continuous/moderate SPL listening.

Examples:

Measurement: 92dB at listening position: SPL JBL LSR 308 - blue, MartinLogan - red

Second harmonic dB relative to fundamental (scaled to 0dB):

upload_2017-11-23_14-7-44.png


Third harmonic dB relative to fundamental (scaled to 0dB):

upload_2017-11-23_14-8-23.png


Anyway, the JBL playing loudly at 10 feet (they are, admittedly, inexpensive nearfield monitors) don't sound so, uh..., clean, as the panels.

At more moderate levels (with room-correcting DSP applied) both sound essentially the same to me, as the level of distortion drops relative to the fundamentals.
 
Last edited:

tomelex

Addicted to Fun and Learning
Forum Donor
Joined
Feb 29, 2016
Messages
990
Likes
572
Location
So called Midwest, USA
I recently talked with Ethan Winer and asked him about these files he had done and he kindly passed the links on to me.

http://ethanwiner.com/audibility.html

and


These are valuable experiments and allow us to better understand distortions vs db down etc. We make a lot about distortions of all sorts, in reality many types are very hard to hear.
 

watchnerd

Grand Contributor
Joined
Dec 8, 2016
Messages
12,449
Likes
10,408
Location
Seattle Area, USA

@Cosmik -- Piano is actually somewhat a pain to record and that gets reflected in the recordings. From "out front" it's not that much harder to record than anything else IMO, but many (myself included) like to be in the pianist's seat when listening to a recording and then it gets harder to decide what and where to mic the thing.

Recording a prepared piano, a la John Cage, is even nuttier.

I once spent the better part of a day moving mics and trimming pots, while the extra bolts and screws moved around, while we argued about what it was supposed to sound like and how, to the artist, none of it sounded like the previous time, or the time before that.

Until we all suddenly realized that lack of repeatability was the whole point.

We then left the mics and bolts in whatever arbitrary position we had last left them and went ahead and made the recording.

Damn you John Cage.
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,198
Likes
16,981
Location
Riverview FL

tomelex

Addicted to Fun and Learning
Forum Donor
Joined
Feb 29, 2016
Messages
990
Likes
572
Location
So called Midwest, USA
Here is some more audible distortion, the big one, the room

Around 3:20 starts getting into the results of the room treatment


here is another one, some more piano to compare in it as well, in a very small room.
 
Last edited:

tomelex

Addicted to Fun and Learning
Forum Donor
Joined
Feb 29, 2016
Messages
990
Likes
572
Location
So called Midwest, USA
I think this might have got by some folks in a couple posts up, here I take you direct to Ethan's great tests for audibility.
For me, the first noise, I lost it at about 40db down, that track was recorded at -1db from full scale, so loud sort of loudness wars.
The next one, the cello, was recorded peaks at about -15 db from full scale, and on that one, could hear down to 70db but not really at -75db, and that was with the music turned up a lot more than I normally would.

His other following audio tests are really great, recommended to help us understand that probably artifacts that are down -75 or at most -80db are inaudible at most listening levels, if not even the most extreme listening levels where you are blowing your ears out. Great stuff on dither and truncation and phase etc as well.

Enjoy,,,, start at 32:00

 
Last edited:

tomelex

Addicted to Fun and Learning
Forum Donor
Joined
Feb 29, 2016
Messages
990
Likes
572
Location
So called Midwest, USA
All distortions or artifacts that sum to a level -80db or lower (example -85db) are inaudible. That is the answer to this thread question, no? Yes?

 

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
14,070
Likes
16,599
Location
Central Fl
I always wanted a oscilloscope to play with, absolutely no idea how to use one, but it's such a KOOL toy! ;)
 

Ethan Winer

Active Member
Industry Insider
Joined
Feb 29, 2016
Messages
142
Likes
181
Location
New Milford, CT, USA
Thanks Tom for carrying the torch. I'll add only one point about the "loudness war" issue. That isn't about normalizing music so the loudest peak hits at 0 dBFS (or close to it). Rather, it's about using compression and other processes to make the average level louder. So soft parts are raised in volume making everything the same, which makes listening tedious and tiring.
 
Top Bottom