When do measurements correlate with subjective impressions

[Jud]

In the Audio Precision seminar at the first RMAF I attended, something like what Paul is talking about in post #4 was presented. Levels of various types of distortion in the signal were increased, and people were asked to raise their hands as the distortion became audible to them.

 

The one that I heard substantially before anyone else was slew rate limiting, and to me it was fingernails-on-chalkboard irritating, while from the reactions of others it seemed fairly innocuous to them. I own Spectral amplification, with a very fast slew rate. This led me to wonder whether I liked the Spectral stuff because I dislike slew rate limiting, or whether owning the Spectral stuff had made me more sensitive to something I was unaccustomed to hearing in my own system.

 

Just wanted to bring this up to raise the general idea that individual sensitivity to various forms of distortion may vary, and so @4est's original question may not have the same answers for everyone.

[Jud]

1 hour ago, pkane2001 said:

It also, has the curious quality of being sensitive to the USB cable I use with it.

 

Measured differences? In what measures? (Curious as to what if any measurable differences a cable might make as part of a system.) Are there any differences between cables that meet spec?

[Jud]

Just now, CG said:

What spec?  🙂

 

USB cables have standard specs they are able to meet, I believe.

[Jud]

1 minute ago, pkane2001 said:

 

Cable I was testing was Lush^2. It made a small but measurable difference in noise level compared to a no-name USB cable. It actually slightly increased the level of noise at the output of the Emotiva DAC. I didn't find Lush^2 to make any difference with other DACs.

 

I assume the increase in noise had to do with shielding/grounding configuration of Lush^2 picking up EMI or introducing a ground loop. (I was using the stock Lush^2 configuration it was shipped with).

 

Of course this raises what's somewhat the flip side of good measurements correlating with subjective good impressions - what types and levels of distortion and noise are euphonic for at least some people? (Beyond the usual mention of tube electronics euphony, there are things like the Aphex Aural Exciter, literally a piece of electronics to produce noise and hash, used in the production of Born to Run, for example.) 

[Jud]

7 minutes ago, CG said:

USB transmission must not be perfect.  Otherwise, why would the designers add all the extra sophistication to correct for errors if there are none?

 

Not an expert, but my impression is that errors would not be small, i.e., not just audio a little less nice, but evident like dropouts, etc.

[Jud]

32 minutes ago, jabbr said:

TL:DR - measure common mode noise transmission/EMI

 

Inexpensive methods of doing so for the home audio enthusiast?

[Jud]

1 hour ago, pkane2001 said:

 

That's precisely why I wrote DISTORT. Measurements are great, but they are just an engineering result, showing how well a device is working. They don't tell the whole story of what's audible, or what distortions I may find pleasant.

 

DISTORT lets me apply controlled levels of various distortions (in any combination) to any music track so I can determine if it rises to audible level while listening on my "perfect" system. Anyone can do the same with this app, with their music, in their system.

 

@Archimago's latest internet blind test is an attempt to do this on a larger scale, gathering input on audibility of various levels of THD. 

 

This is a(nother) wonderful tool, though we might have to get at least one step more sophisticated to get to where we could be relevant to the subjective listening experience.

 

What I mean is that when we listen to audio, we are trying to hear music rather than trying to hear distortion. So learning at what level distortion is audible is of course a good thing, but it may not be the same as the level at which it affects the experience of listening to the music. Using DISTORT in combination with DeltaWave to compare two files where one has a level of noise higher than the other (but still below audibility) might do it.

 

[Jud]

@pkane2001, I was wondering three things:

 

1. Are you reasonably sure from measurements and/or listening that the jitter in DISTORT sounds like the jitter in actual DACs?

 

2. What (other) forms of distortion does jitter cause?

 

3. Can you provide a subjective description of what jitter and the distortion(s) it causes sound like?

 

First question is pretty much for Paul; if others have reasonably *precise* answers, feel free to jump in on the other two.

[Jud]

14 minutes ago, pkane2001 said:

That's not very interesting to anyone. Try it yourself and you tell me.

 

All I can say is that it becomes an audible problem in my testing only when the amount is really large.

 

It's interesting to me, and I'll tell you why.

 

You ask someone new to astronomy to watch through a telescope for an asteroid. They ask "What does one look like through a telescope of this power? What should I watch for?" Your reply is "That's not very interesting to anyone. Try it yourself and you tell me." What are their chances of spotting an asteroid?

 

Replay that last conversation. Your response now is "Let me show you several examples so you get a sense of what to watch for." What are their chances of spotting an asteroid now?

 

So Paul, are you hearing the effects of jitter only at higher levels because it's only ever audible to humans at those levels, or because no one has trained you to notice what lower levels of jitter sound like?

 

What's the training effect? It seems to me this becomes important in determining whether we can be subconsciously affected by levels of distortion we haven't been trained to consciously notice.

[Jud]

On 2/20/2020 at 6:48 AM, pkane2001 said:

But how can I tell if I can't hear low-level jitter because of lack of training or because it's not audible to me, or inaudible to everyone? How could I possibly know the answer to that? 

 

That's an interesting question to me, and I've done some thinking about it. There are at least a handful of people here who've done some work that might sensitize them to jitter.

 

@barrows I believe may have been involved in testing audibility of jitter at PS Audio (though I could be mistaken about that).

 

@jabbr has written that what he calls "close-in jitter" may be particularly important.

 

@Miska and @PeterSt I would imagine have listened for the effects of jitter quite a lot in their testing of software and hardware. @Miska in particular has talked about the effects of correlated jitter (and I've read about this elsewhere too).

 

@JohnSwenson and @Superdad have worked on hardware that purports to reduce jitter and noise.

 

I was wondering whether any of them might know or be able to guess what level of a particular type of jitter would reliably be audible to them, and if it would be possible to produce files simulating these types of jitter that would serve to test their guesses or statements in this regard, if they were willing.

 

That might move us along the road to figuring out what levels and types of jitter are audible to people with training, and therefore could be subconsciously audible and affect the listening experience even for those without such training.

[Jud]

17 minutes ago, barrows said:

Testing i was involved in at PS Audio was not quite so specific.  We basically used a source (same source component with different clocks inside, and sometimes different software running the async clocking-this was during the development of the memory disc player), via SPDIF and/or I2S, which we knew the jitter measurements of, and correlated the measured jitter of those sources with what we heard in the listening room.  My main take away was that lower jitter, or more correctly lower the close in phase noise (low frequency phase noise) always sounded a little better (at least to as low as we could go at the time)  

The Avalon Eidolon speakers were very helpful with this, as a lot of the differences were related to soundstage parameters' and the Avalons were sound staging champs in the well treated PS Audio listening room.  I was sad when they sold those speakers, i really enjoyed them.   

 

Any recollection what sort of jitter levels (nanosecond range, lower?) you were dealing with?

[Jud]

14 hours ago, barrows said:

Some digital products, which measure poorly on standard measurements, but audiophiles seem to like how they sound, may be "sounding good" by doing either: masking the artifacts via the allowance of "pleasant" distortions,

 

They may not have to be pleasant. I remember a post you made a long time ago (you may not remember it or the events you recounted yourself, but perhaps you do) saying that in the PS Audio jitter tests at least some people liked more jitter. In a little test here of 3 pairs of files, both @bluesman and I picked the files with more jitter as sounding better. To me they sounded more "natural" and "dynamic." I make no representations that my own hearing and taste is any good, but @bluesmanis a professional musician with decades of experience who once on this forum accurately picked out the size of a grand piano from a recording. So what was it about the extra jitter in those files that made them sound more realistic to him, or was the result purely random?

[Jud]

By the way - there are just acres and acres of possibly relevant academic psychoacoustic research into potentially relevant topics, so don't lament that no one's looked into any of this, get out there and see if they possibly have.

 

I've run across about 60 published articles in peer reviewed journals or books from academic presses that are of interest to me so far. The knowledge you're wanting may indeed be "out there," and accessible to you.

[Jud]

6 hours ago, Audiophile Neuroscience said:

Hi Jud

Agreed there are acres of psychoacoustic and pschophysics papers. Do you have any references for the OP question?

Cheers

David

 

Not direct answers, no. It hasn't been a topic I've looked at.

[Jud]

On 2/23/2020 at 1:25 PM, Iving said:

What we know from @Jud's story this time around (apart from not much!):

 

Finally getting back around to this - apologies for the delay.

 

On 2/23/2020 at 1:25 PM, Iving said:

- There were three pairs of music files each pair having a jitter differential.

- Jud and bluesman liked the jitter files better - we don't know whether there were more "subjects" than just Jud and bluesman

 

Yes. Open to anyone on the forum, though I don't recall how many participated.

 

On 2/23/2020 at 1:25 PM, Iving said:

- we don't know whether there was "statistical power" in the set-up - very unlikely from the sounds of it - even if there was and we can say with confidence that jitter files are preferred - then the possible reasons for that can be investigated as a separate line of argument.

 

I doubt it too, and the "experimental protocol" was quite informal, so...

 

On 2/23/2020 at 1:25 PM, Iving said:

- According to Jud, bluesman "once on this forum accurately picked out the size of a grand piano from a recording" - Jud says "So what was it about the extra jitter in those files that made them sound more realistic to him, or was the result purely random?" - but it is not clear whether bluesman's discernment feat occurred with the jitter pairs or with just some music file not connected with the jitter tests.

- Either way, we can regard bluesman's discernment feat as both impressive and interesting.

- If it was with a non-test file, interpretation is simpler.

 

It was with a non-test file, one of Mario Martinez' excellent Truthful Master demos or PlayClassics recordings - see e.g. 

 

 

As I noted, he's been a professional musician for decades and has a fine ear for a piano. This of course doesn't prevent him from being wrong half the time or mean his selection of 3 files with more jitter in another listening experience wasn't just a random occurrence. For me it falls into the category not of "probative," but of "interesting, wonder if it might have any significance at all?", since being fooled by euphonic distortion is something I'm interested in.

 

Here's something related I'm interested in, illusions. I wonder if there are audio equivalents to the visual demonstration below, where inaccurate amplitude (brightness) and frequency (color) *looks* accurate. Are there inaccuracies (besides sheer loudness) that sound closer to the "real thing" to us than accurate reproduction? If so, which should we strive for - that which sounds real, or that which is accurate?

 

 

[Jud]

1 minute ago, jabbr said:

We should get the choice!

 

Accuracy is more objective. What sounds “real” could be subject to the whims of someone else making a decision eg MP3

 

I mean "real" on the scale of an illusion like the one in the video above, that appears accurate to pretty much everyone who sees it. Are there audible illusions that sound more like the "real thing" than an accurate reproduction to virtually everyone who hears them?

[Jud]

@kumakuma, maybe you don't want to be the other half of this dialog. We understand what's happening and are capable of ignoring it, or in @4est's case, capable of handling the thread.

[Jud]

1 hour ago, lucretius said:

 

There are audio effects (added during mastering):

• uses of delay for filling out a performance, especially vocals or guitar
• reverb can add fullness, spaciousness and depth to a sound
• a stereo chorus can widen your stereo image
• distortion can makes the sound fatter and fuller, adding body

 

Are these audio illusions or are you referring to something else?

 

I don't think they are in the strict sense. The visual illusion I posted is something your brain can't avoid doing even when you know what's happening. Such illusions give us information about how the brain processes sensory input. For illusions more along the lines I'm thinking of, see http://deutsch.ucsd.edu/psychology/pages.php?i=201

[Jud]

3 hours ago, jabbr said:

Ever been to a concert with an electric guitarist who moves about the stage with microphone? If you sit close up, the sound appears to come directly from the mouth and guitar. Yet the guitar amp and mic amp remain in a fixed position on stage. Soundstage is truly an illusion!

 

True, but unless you're watching a DVD or Blu-ray, the illusions at home must be purely audible. I'd still like to tie this to the very interesting question in the original post - whether any such illusions would correspond with particular distortion measurements.