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What measurements correlate with X?

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2 hours ago, jabbr said:


IMD is one of the non linear distortions that is not measured on the typical AP analyzer FFT. Inter modulation distortion is not the side band/harmonic spectra surrounding a pure tone rather depends on interactions between tones. Think about distortion/soundstage breakdown when too many instruments are playing at the same time. 

You really hit the nail on the head.  I am NOT meaining to bring in my DA project, but the normal DolbyA mushes up the instruments and vocal chorus together when trying to decode an encoded recording.  VERY GREAT LENGTHS were made on the DA  project to keep that from happening.  The decoder actually moves the sidebands around in weird/Hilbert transform ways and also keeps the gain control ripple from modulating the signal -- the work to make sure that the distortion isn't created was 10X more complex than doing a DolbyA decode itself.

 

Any time that a signal has been touched by DolbySR, DolbyA, DolbyB, DolbyC, Telcom C4 and DBX to a lesser extent, the signal gets spread over frequency and time to produce a 'softer' or sometimes even a 'grinding' sound in the worst case.

 

The old NR systems are a definite devils bargain, and a gross source of IMD distortion.   Slow AGC systems are not very bad in this regard, but whenever the attack times start approaching faster than the 10msec region (because the spectrum of the attack is faster than 100Hz), then the softening starts happening.   When the attack and release times are very fast, then the energy adds up rapidly.

 

John

 

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I of course disagree with John - if you want to want to call the distortion anomalies IMD that's fine - but this "IMD" as audible unpleasantness is a function of the integrity of the playback chain, irrespective of the nature of the recording - a sub-par setup will make a very high percentage of recordings irritating to listen to, AND lose much of the musical detail; if the integrity of the chain is lifted to a high enough level, then you win everywhere: all the detail is perfectly clear, tonality is fully natural, and every recording becomes a pleasure to listen to.


Frank

 

http://artofaudioconjuring.blogspot.com/

 

 

Over and out.

.

 

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41 minutes ago, Allan F said:

 

At the risk of repeating what many have posted on numerous occasions in different threads, the notion that any system can make every recording "a pleasure to listen to" is complete and utter nonsense.

 

This is a motto I use, which prevents me from "giving in" when I come across a recording which seems particularly unpleasant - now, it could be the intended consequence of the recording to be unpleasant to the ears; or the unintended consequence of very poor or unskilled mastering to make it borderline acceptable - extremely badly done compression, say - I'm presuming that the desire of the people making the recording was that at least a percentage of people hearing it wouldn't be repulsed ... but that may be a mistake, of course 😁.


Frank

 

http://artofaudioconjuring.blogspot.com/

 

 

Over and out.

.

 

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11 hours ago, jabbr said:


IMD is one of the non linear distortions that is not measured on the typical AP analyzer FFT. Inter modulation distortion is not the side band/harmonic spectra surrounding a pure tone rather depends on interactions between tones. Think about distortion/soundstage breakdown when too many instruments are playing at the same time. 

 

There is a slow move in the general direction though. Multitone tests (32 tones, nowhere close to real orchestral or choral music) have become more commonplace in recent years. AP had that capability even when I was in the industry (1990s) - its taken almost 3 decades for it to become virtually mainstream.

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8 hours ago, jabbr said:

 

You of course disagree with John because he is being specific and your world consists only of generalities unique to yourself. “IMD” isn’t just vague “distortion anomalies” but a specific type of distortion. 

 

Yes, a specific type of distortion, to wit, "caused by nonlinearities or time variance in a system". But his software doesn't correct that, because the IMD can't be in the music data; it only occurs because of a faulty reproduction chain, processing the type of data.

 

Thank you for having me chase that down ... it caused me to revisit a named distortion issue which is one of the key ones I worry about - PIM. That is, Passive Intermodulaton Distortion, the Rusty bolt effect ... I came across this in the literature some time ago, and then it dropped out of my awareness, as something that is studied.

 

8 hours ago, jabbr said:


“Pleasure” is how you personally perceive it. Your “system” works for you to achieve your own pleasure regardless of the recording — your pleasure is not a function of the specific musical input, rather the efforts you make to arrange your “rig”. 
 

That’s all well and good but doesn’t help those who are seeking an audio reproduction system which reproduces the recordings. 

 

What I hear are the recordings - otherwise, what I do to a rig is unbelievably, mindbogglingly complex ...it makes every recording sound very different, changes the tonal and acoustic signature of each one, and does this 100% consistently ... gosh, it might mean I'm really much, much cleverer than I think, 😉.


Frank

 

http://artofaudioconjuring.blogspot.com/

 

 

Over and out.

.

 

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On 3/4/2020 at 6:08 AM, John Dyson said:

I am glad that you mentioned IMD as a source of damage to a stereo image -- I have been developing software that in it's natural, most degenerate state will produce IMD very easily.   Even a slight amount of IMD has a strong effect on the ambiance/clarity of a recording.   Clarity has somewhat of an effect on imaging.   IMD damages something good about audio that I have problems actually describing, and it doesn't take much of the IMD to do the damage.

 

IMD is insidious...  IMD isn't just insidious, it is develishly insidious.   Given a minor about of IMD, I have difficulty in detecting it unless doing a direct A/B comparison.   Some forms of IMD appear as a 'fog' over the sound (if I can get my act together when I am less busy, I might be able to create an example.)  It is really interesting what happens to audio when it has been processed in certain ways.  Those forms of processing were ALMOST thought to be benign, but really were/are not benign at all.   Some methods (unfortunately sometimes necessary to do), produce very stealthy, but damaging IMD type distortions.

 

Since ambiance is significantly affected by certain kinds of IMD behaviors, then it can have some effect on the image.

This is actually one of my own frustrations against alot of commercial recordings.

 

John

 

 

john,

can you give us a ballpark idea of what levels of IMD can cause the problems you describe?

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On 3/4/2020 at 5:19 PM, fas42 said:

I of course disagree with John - if you want to want to call the distortion anomalies IMD that's fine - but this "IMD" as audible unpleasantness is a function of the integrity of the playback chain, irrespective of the nature of the recording - a sub-par setup will make a very high percentage of recordings irritating to listen to, AND lose much of the musical detail; if the integrity of the chain is lifted to a high enough level, then you win everywhere: all the detail is perfectly clear, tonality is fully natural, and every recording becomes a pleasure to listen to.

 

what is that 'high enough level'?

has anyone quantified it?

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1 hour ago, cat6man said:

 

what is that 'high enough level'?

has anyone quantified it?

 

Unfortunately, no-one can quantify it, as yet. And, it most likely will vary per individual - some may never experience it, no matter how "perfect" the playback is, because of how their brains are wired.

 

In simple terms, it needs the playback chain to be extremely free of various subtle distortion and noise contributions by the electronics, ones which disturb the listening mind - currently, the only way to achieve this is by very careful assessment, and refinement of areas of the circuits which are below the necessary quality level. Yes, this is very general; but it's impossible to provide a set of numbers which guarantee the performance; nor what should be done in each case.


Frank

 

http://artofaudioconjuring.blogspot.com/

 

 

Over and out.

.

 

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8 hours ago, cat6man said:

 

john,

can you give us a ballpark idea of what levels of IMD can cause the problems you describe?

I should probably measure it -- but it isnt very much.  It is the amount that is generated by a gain control at approx 1msecs attack/40msec rleease over a 10dB gain range.  (I cannot get more specific than that.)  It is very repeatable -- everytime you hear a DolbyA decoded tape, you are hearing it (sadly.)  Maybe that is why they dont decode much pop music, but just EQ it away?

 

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4 hours ago, John Dyson said:

I should probably measure it -- but it isnt very much.  It is the amount that is generated by a gain control at approx 1msecs attack/40msec rleease over a 10dB gain range.  (I cannot get more specific than that.)  It is very repeatable -- everytime you hear a DolbyA decoded tape, you are hearing it (sadly.)  Maybe that is why they dont decode much pop music, but just EQ it away?

 

 

thanks.......i'm very (or rather, was a very long time ago) familiar with the SQ degradation of DolbyA.

 

if you do measure it, could you try to get a peak as well as average measurement?  in most cases, i have a very low comfort level with the idea that average measurements capture the types of SQ effects i'm interested in.

in other words, i believe good average measurements are necessary but not sufficient.

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10 minutes ago, cat6man said:

 

thanks.......i'm very (or rather, was a very long time ago) familiar with the SQ degradation of DolbyA.

 

if you do measure it, could you try to get a peak as well as average measurement?  in most cases, i have a very low comfort level with the idea that average measurements capture the types of SQ effects i'm interested in.

in other words, i believe good average measurements are necessary but not sufficient.

DolbyA was definitely a devils bargain.   One thing about the DA/FA decoder is that the *lowest* quality mode produces less foggy sound (only by listening tests) than true DolbyA.   At the highest quality mode (takes lots of CPU, lots of sideband cancellation & shifting), there is no fog.   I have done A/B (admittedly not adequately scientific), and you can almost *really* get the original recording back with the DHNRDS DA.

 

It is a different animal (mathematically) from a simple HW jFET feedback compressor, very different.   The worst mode on the DHNRDS smooths the attack waveform and recenters the timing perfectly so that it trades off an overly fast attack which just spreads sidebands for an attack that better maintains the signal integrity.

Also, the DolbyA detector actually produces it's own intermod -- it really surprised me...   I re-did the input detector to have EXACTLY the same attack/release time, but no 'wobbles' in the attack/release waveform.

Then, after all of that, in the highest quality modes, as the gain * signal calculation is done, there are some Hilbert transform games that hide/shift the sidebands into audible non-existance!!!

The DA decoder also produces ZERO intermodulation splats.  If you start with a signal that is limited to 24kHz, you won't get splats above 24kHz (nor below.)

 

The DolbyA HW design had a basic deficiency in the DECODING process, but the encoding process was pretty clean.  The decoding mechanism had delays that arent' compensated for anywhere, and so the feedback loop that creates the expander from the compressor array is defective.

 

There is really NO WAY for DolbyA HW to retrieve what was recorded.   The DA decoder comes closer, but I never claim perfection (but it is :-)).

 

John

 

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On 3/4/2020 at 5:52 PM, jabbr said:


IMD is one of the non linear distortions that is not measured on the typical AP analyzer FFT. Inter modulation distortion is not the side band/harmonic spectra surrounding a pure tone rather depends on interactions between tones. Think about distortion/soundstage breakdown when too many instruments are playing at the same time. 

 

Many (most?) audiophiles do not listen to orchestral music, large choirs or jazz bands.

 

This perhaps explains why equipment which produces high quantities of IMD can still be popular.


"Science draws the wave, poetry fills it with water" Teixeira de Pascoaes

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9 hours ago, semente said:

 

Many (most?) audiophiles do not listen to orchestral music, large choirs or jazz bands.

 

This perhaps explains why equipment which produces high quantities of IMD can still be popular.


I can’t say that it’s just IMD but I’ve also compared  rock (eg Yes:Roundabout) across different systems inclusive different live arenas and I’ve heard the music “breakdown” during complex passages. 


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