DSP Crossover Neurosis: Intervention Needed
Nov 27, 2016 at 1:48 AM Thread Starter Post #1 of 29

watchnerd

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So I'm in the midst of planning my next upgrade and am seriously thinking of saying "good-bye" to my power amps and passive speakers and going full active powered speakers.
 
My sources are: streaming digital audio and vinyl
 
Two of the finalist speakers I'm considering have analog XLR inputs (no digital input), with DSP-based crossovers, followed by a PWM amplifier.
 
This leads to the following facts:
 
1. Incoming will pass through an A/D converter running at 24bit/96khz.
 
2. Analog signals (vinyl) will be converted to digital
 
3. Digital signals will go from D/A (from my DAC) and then A/D again before final amplification.
 
 
This leads to the following set of back and forth dilemmas in my own head:
 
1. Vinyl will be converted to digital.  Oh noes!
 
2. #1 doesn't really matter that much given how many recent issues of vinyl were remastered on a DAW (i.e. digitally) anyway.
 
3. You don't really believe in the "digital can't really capture analog wave forms" schtick, anyway, right?  Lossless is lossless.
 
4.  The A/D conversion is Delta-Sigma, which would make a multibit DAC pointless, wouldn't it? (even asked Schiit about it).
 
5. Does #4 matter?  Or if it matters, does it matter more than the measurable benefits of using a DSP crossover with perfect phase and more perfect flat response?
 
6. You have a quality DAC with low jitter...but how good is the jitter in the ADC in the speakers/crossover?  
 
7. Isn't going D->A and then A->D just adding complexity, and potentially more noise or errors?
 
8.  For #7, if A->D is such a problem, why do we think it works flawlessly during the recording process?
 
9. Do you think the ADC in the speaker is as good as what they use in recording?
 
10. Is all of this just neurosis when what really matters most are the recording, the acoustics of the room, and the response curves, dispersion, distortion, and rise times of the transducers (i.e. the speakers and the cartridge)?
 
 
Please feel free to dissect, disagree, deconstruct or confirm any of the above.
 
Nov 27, 2016 at 4:30 AM Post #2 of 29

castleofargh

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dunno if you'll have great success on headfi when talking about speakers.
 I'm a fan of active speakers and a fan of DSPs in general, so I'm clearly biased here ^_^.  I can't see why going one more time thought ADC and DAC would compromise audible transparency. in the grand scheme of an audio chain, those are still the very best elements when it comes to fidelity. when I measure my gears, I do DAC to ADC instead and the results are pretty great despite both being on the cheap side of things. so I can only be optimistic about that extra conversions. sure it's bad in idealistic theory, but when comparing that to the fidelity of drivers in a room, or the fidelity of vinyls, it feels like we're looking at the wrong magnitudes of fidelity. if doing all that in the speakers can really optimize the crossovers and the response of the drivers, then it's most likely a good thing IMO.
 
jitter, discrete dac, or digital conversion of vinyls, now those are clearly in my list of "I do not care at all". I'd sooner put a few more pillows in my room pretending I'm doing room treatment, than worry about how I ruined my music with jitter or DS conversion. I truly believe my pillows will play a bigger role(good or bad).
 
Nov 27, 2016 at 6:09 AM Post #3 of 29

pinnahertz

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  So I'm in the midst of planning my next upgrade and am seriously thinking of saying "good-bye" to my power amps and passive speakers and going full active powered speakers.
 
My sources are: streaming digital audio and vinyl
 
Two of the finalist speakers I'm considering have analog XLR inputs (no digital input), with DSP-based crossovers, followed by a PWM amplifier.
 
This leads to the following facts:
 
1. Incoming will pass through an A/D converter running at 24bit/96khz.
 
2. Analog signals (vinyl) will be converted to digital
 
3. Digital signals will go from D/A (from my DAC) and then A/D again before final amplification.
 
 
This leads to the following set of back and forth dilemmas in my own head:
 
1. Vinyl will be converted to digital.  Oh noes!
 
2. #1 doesn't really matter that much given how many recent issues of vinyl were remastered on a DAW (i.e. digitally) anyway.
 
3. You don't really believe in the "digital can't really capture analog wave forms" schtick, anyway, right?  Lossless is lossless.
 
4.  The A/D conversion is Delta-Sigma, which would make a multibit DAC pointless, wouldn't it? (even asked Schiit about it).
 
5. Does #4 matter?  Or if it matters, does it matter more than the measurable benefits of using a DSP crossover with perfect phase and more perfect flat response?
 
6. You have a quality DAC with low jitter...but how good is the jitter in the ADC in the speakers/crossover?  
 
7. Isn't going D->A and then A->D just adding complexity, and potentially more noise or errors?
 
8.  For #7, if A->D is such a problem, why do we think it works flawlessly during the recording process?
 
9. Do you think the ADC in the speaker is as good as what they use in recording?
 
10. Is all of this just neurosis when what really matters most are the recording, the acoustics of the room, and the response curves, dispersion, distortion, and rise times of the transducers (i.e. the speakers and the cartridge)?
 
 
Please feel free to dissect, disagree, deconstruct or confirm any of the above.

1. Vinyl will be converted to digital.  Oh noes!
 
2. #1 doesn't really matter that much given how many recent issues of vinyl were remastered on a DAW (i.e. digitally) anyway.
 
Or even "worse", all vinyl mastering requires the use of a "preview" signal one disc rotation in advance of the cutter.  That usually means the cutter signal has been passed through a digital delay.  That's pretty much all of it these days.
 
3. You don't really believe in the "digital can't really capture analog wave forms" schtick, anyway, right?
 
The "digital can't capture ananlog" stance is usually taken by someone who thinks the signal coming out of a DAC is full of "bits" and stairstep waveforms.  It isn't, and never has been.  The fact is, even lowly red book digital can capture more of the analog waveform with less corruption/distortion than any analog recording system known to man, tape and vinyl specifically included.  
 
 Lossless is lossless.
 
Well, yes, but the A/D process isn't lossless, it's just really really good, better than any analog recording system known to man. 
 
4.  The A/D conversion is Delta-Sigma, which would make a multibit DAC pointless, wouldn't it? (even asked Schiit about it).
 
5. Does #4 matter?  Or if it matters, does it matter more than the measurable benefits of using a DSP crossover with perfect phase and more perfect flat response?
 
Does it matter? Nope.  The speaker itself is the limiting quality factor in terms of distortion and frequency response, by a lot.  Getting the response flat (or rather, to the correct target curve) in the room is very important.  Doing it with perfect phase is impossible, but improving the phase response of the total system (including the room) is an admirable, if barely audible, goal.  All of this outweighs the nano-differences in ADC/DAC technology. 
 
6. You have a quality DAC with low jitter...but how good is the jitter in the ADC in the speakers/crossover?  
 
Probably darn good.  Don't know for sure, but you can measure it pretty easily.  But you're listening to vinyl, right?  You might not be aware, but there's an analog equivalent of digital jitter, it's all over all those analog recordings, and it's a far bigger problem than any digital jitter.  High frequency speed variations that occur in analog tape moves across stationary heads and guides (an anomaly called "scrape flutter") introduces an FM component, which becomes easily audible as noise around mid-high frequency tones.  There's no way to get rid of it once it's there.  It has to be eliminated or reduced at the recorder mechanically with a tape path that includes lots of roller guides, and very little stationary components. But you've got it on those "pure" analog recordings, just a question of how much.  I wouldn't worry about jitter in your ADC in your speakers.  
 
7. Isn't going D->A and then A->D just adding complexity, and potentially more noise or errors?
 
Technically, yes.  That's not asking the question correctly, though.  It should be "is the additional noise and errors caused by A/D and D/A cycles audible above system noise, room noise, etc?"  And that answer would be "No".   The typical listening room and system will be room-limited to an 80dB or less max SPL to noise ratio. Typical is 65dB-70dB. 
 
8.  For #7, if A->D is such a problem, why do we think it works flawlessly during the recording process?
 
I, for one, don't think A/D is a problem, and hasn't been for several decades.  The recording process isn't technically flawless, but once the flaws are below the threshold of audibility, the job is done.
 
9. Do you think the ADC in the speaker is as good as what they use in recording?
 
That would depend on what was used for recording, when the recording was made, etc.  Todays ADCs are spectacular compared to the ADC ca 1985.  But they don't have to be all that great in speaker anyway.  Effective 20 bits is all you'll ever get in any practical ADC, even for recording.  
 
10. Is all of this just neurosis when what really matters most are the recording, the acoustics of the room, and the response curves, dispersion, distortion, and rise times of the transducers (i.e. the speakers and the cartridge)?
 
Yup.  But let me put the factors in order of impact on the end result:
 
1. Speaker performance (lets include the entire system of amp, transducer, DSP, transient response, off-axis response, the works...it's one system in the end)
2. Room acoustics - the best speakers in a bad room won't ever sound their best
3. The resulting speaker > room performance.  Response curve, certainly, but also dealing with aiming, early reflections, resonances, modes, etc. This one includes speaker positioning, and listening position
4. Cartridge - proper calibration to the preamp (nobody pays enough attention to this one).  Proper geometry and force, then confirmed RIAA curve tracking and channel match.  
5. The rest of your electronics
 
Speakers response in a room is generally the leasts flat of anything in the system.  Speaker distortion is 1000X that of any well-designed electronic piece operating within design parameters (vinyl distortion is a close second, though).  Small changes in position and room acoustics make huge audible differences.  Nothing else you tweak has that kind of impact.  
 
Nov 27, 2016 at 10:42 AM Post #4 of 29

watchnerd

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I'd sooner put a few more pillows in my room pretending I'm doing room treatment, than worry about how I ruined my music with jitter or DS conversion. I truly believe my pillows will play a bigger role(good or bad).

 
LOL.  This needs to go in someone's signature.  Along with the proper use of curtains.
 
 
 I'm a fan of active speakers and a fan of DSPs in general, so I'm clearly biased here ^_^.  
 

 
One other benefit of active speakers -- it neutralizes cable craziness.  There are no expensive speaker cables to be used or worried about.  And for XLR balanced cables, this seems to be one area where the audiophile cable mafia has had no traction -- I don't know of any expensive voodoo laden XLR cables.  I just use good, but modest priced, pro stuff (Canare, Belden) or Monoprice.
 
 
 
 
6. You have a quality DAC with low jitter...but how good is the jitter in the ADC in the speakers/crossover?  
 
Probably darn good.  Don't know for sure, but you can measure it pretty easily.  But you're listening to vinyl, right?  You might not be aware, but there's an analog equivalent of digital jitter, it's all over all those analog recordings, and it's a far bigger problem than any digital jitter.  High frequency speed variations that occur in analog tape moves across stationary heads and guides (an anomaly called "scrape flutter") introduces an FM component, which becomes easily audible as noise around mid-high frequency tones.  There's no way to get rid of it once it's there.  It has to be eliminated or reduced at the recorder mechanically with a tape path that includes lots of roller guides, and very little stationary components. But you've got it on those "pure" analog recordings, just a question of how much.  I wouldn't worry about jitter in your ADC in your speakers.  
 

 
I'm not only listening to vinyl; I'm also listening to streaming lossless digital, either from local NAS (FLAC and ALAC) or from a lossless Tidal subscription.  All played via Roon.
 
Regarding vinyl, though....you also reminded me of the wow&flutter of the turntable, which has speed variations of .02% from true (i.e. from perfect 33 1/3 RPM), wow & flutter of .04%, and SNR of -77 dB.
 
I don't know how that translates to how many picoseconds of jitter, but I'm sure the "analog jitter / wow / flutter" would be atrocious of stated in digital terms.
 
   
9. Do you think the ADC in the speaker is as good as what they use in recording?
 
That would depend on what was used for recording, when the recording was made, etc.  Todays ADCs are spectacular compared to the ADC ca 1985.  But they don't have to be all that great in speaker anyway.  Effective 20 bits is all you'll ever get in any practical ADC, even for recording.  
 

 
The A/D converter used in the speakers is a Burr-Brown PCM 1804 (24bit Delta Sigma A/D converter). As always, the devil is in the implementation, but, yeah, compared to the ADCs used on some of my "vintage digital" recordings, the specs are much much much much better than the analog portions of my system.
 
 
 
4. Cartridge - proper calibration to the preamp (nobody pays enough attention to this one). 

 
I'm one of those.  My phono stage is not fully configurable for load and capacitance. Getting a phono stage that allow for full configurability is on my wishlist and probably far more rational to waste mental energy on than all of this DSP/active speaker stuff.
 
  Speaker distortion is 1000X that of any well-designed electronic piece operating within design parameters (vinyl distortion is a close second, though). 

 
Distortion specs for speakers are frustratingly hard to get, but they are something I look for.  Fo most of the good ones I'm looking at, at 90 dB SPL @ 1m, are about 1% THD in the bass roll off region (- 3dB point), asymptotically higher below that, and 0.2% to 0.5% in the mids and highs at that SPL.  That's 100x worse than the THD of the DAC, preamp, or the headphone amp.
 
Nov 27, 2016 at 1:58 PM Post #5 of 29

pinnahertz

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Quote:
I'm one of those.  My phono stage is not fully configurable for load and capacitance. Getting a phono stage that allow for full configurability is on my wishlist and probably far more rational to waste mental energy on than all of this DSP/active speaker stuff.
 
Good for you!  You're about 3/4 of the way there.  You need to measure the final result with a test record, preferably recorded without RIAA eq.  Get that right, you're done.
 
 
 
Distortion specs for speakers are frustratingly hard to get, but they are something I look for.  Fo most of the good ones I'm looking at, at 90 dB SPL @ 1m, are about 1% THD in the bass roll off region (- 3dB point), asymptotically higher below that, and 0.2% to 0.5% in the mids and highs at that SPL.  That's 100x worse than the THD of the DAC, preamp, or the headphone amp.

Speaker THD is hard to get because it looks so bad.  the 90dB @1m would be the best it would look.  Lower levels and you can't get good THD because of noise in the measurement, higher levels just look worse.  1000x might have been a bit of exaggeration, but at extreme LF at real listening levels, probably not.
 
Nov 27, 2016 at 5:13 PM Post #6 of 29

Roseval

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  One other benefit of active speakers -- it neutralizes cable craziness.  There are no expensive speaker cables to be used or worried about.  And for XLR balanced cables, this seems to be one area where the audiophile cable mafia has had no traction -- I don't know of any expensive voodoo laden XLR cables.  I just use good, but modest priced, pro stuff (Canare, Belden) or Monoprice.
 

Are you sure?
What about 2 audiophile power cords?
What about some balanced cables starting at $2800,- ? http://store.transparentcable.com/audio/ultra/balanced-interconnect/
 
Nov 27, 2016 at 5:42 PM Post #7 of 29

watchnerd

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  Are you sure?
What about 2 audiophile power cords?
What about some balanced cables starting at $2800,- ? http://store.transparentcable.com/audio/ultra/balanced-interconnect/

 
I stand corrected...I had no idea there were super-premium XLR cables.  I guess that shows my pro audio bias.
 
$3380 for a 10 ft pair, vs $38 for 10 ft of Canare Star Quad with Neutrik connectors from Blue Jeans Cable, or $7.74 for basic XLR cables from Monoprice.
 
I shouldn't be surprised any more, but yet I continue to be.... 
confused_face_2.gif

 
Nov 27, 2016 at 6:06 PM Post #8 of 29

pinnahertz

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  Are you sure?
What about 2 audiophile power cords?
What about some balanced cables starting at $2800,- ? http://store.transparentcable.com/audio/ultra/balanced-interconnect/

There is no area that the audio maphia has not had its fingers into.  Any non-Voodoo-laden cable may have the Voodoo added for a slight up-charge.  There's even an outfit (or guy) who will do the upgrade remotely without ever touching or even visiting your system.  
 
I believe the active bio-organism Voodoo additive product is called "Scamatazoa"...or something.  
 
Now stop talking about this before we have all our kneecaps broken.  
 
Nov 29, 2016 at 6:15 AM Post #10 of 29

gregorio

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  The A/D converter used in the speakers is a Burr-Brown PCM 1804 (24bit Delta Sigma A/D converter). As always, the devil is in the implementation ...

 
To be honest, not really. I don't know of any implementations remotely that bad!
 
While I entirely agree with the general premise on pinnahertz's post, I'm going to disagree on some of the finer details. Room acoustics blows everything else out of the water. A world class studio will have several peaks and troughs in it's frequency response of at least 10dB, the average untreated home listening environment will have numerous peaks and troughs throughout the audible band, the worst of which are probably at least 30-40dB and countless others of 10dB+. Speaker distortion is way less than that. Your turntable is way less than the speaker distortion and digital conversion way less than your turntable. That's a lot of "way lesses" multiplied together, to the point of silliness! In total, we're probably talking about considerably more than 1,000x. Worrying about say the jitter of an ADC in this context is a bit like worrying about an invisible/microscopic flaw in the paintwork of a car which has just come out of an industrial crusher!
 
G
 
Nov 29, 2016 at 7:07 AM Post #11 of 29

pinnahertz

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To be honest, not really. I don't know of any implementations remotely that bad!
 
While I entirely agree with the general premise on pinnahertz's post, I'm going to disagree on some of the finer details. Room acoustics blows everything else out of the water. A world class studio will have several peaks and troughs in it's frequency response of at least 10dB, the average untreated home listening environment will have numerous peaks and troughs throughout the audible band, the worst of which are probably at least 30-40dB and countless others of 10dB+. Speaker distortion is way less than that. Your turntable is way less than the speaker distortion and digital conversion way less than your turntable. That's a lot of "way lesses" multiplied together, to the point of silliness! In total, we're probably talking about considerably more than 1,000x. Worrying about say the jitter of an ADC in this context is a bit like worrying about an invisible/microscopic flaw in the paintwork of a car which has just come out of an industrial crusher!
 
G

The effect room acoustics has on frequency response - the "peaks and dips" referred to - do not occur throughout the audible band.  Room modes affect lower frequencies only, and the point below which room modes become dominant is well known as the Schroeder frequency.   Below the Schroeder frequency room modes affect the total response (depending on location) because of room modes effect on discrete frequencies, above Schroeder, room modes overlap and become room reverb.    I've never measured a home listening room with a 40dB dip in response.  Ever. Sometimes there are greater than 10dB dips and peaks (20dB variation total) measured in a single location, a problem often cured with minor physical adjustment.   Pro studios do not have 10dB troughs unless they haven't been properly tuned.  While there are many of those rooms, again, the critical mix position can usually be smoothed out with a trap or two, or the use of multiple subwoofers that can be properly positioned.  In a mixing studio we tune for a relative small LP, the mix position.  In home theater, we tune for all seats with somewhat greater tolerance.
 
 A good reference paper on this would be "First Results from a Large-Scale Measurement Program for Home Theaters" by Holman and Green, AES, November 2010.  Data was taken from measurements of over 500 rooms, multiple positions for each.  The average Schroeder frequency ended up around 200Hz, reverb time under .3 seconds.  
 
The character of a speaker is primarily determined by it's upper bass through HF response, and only slightly less by it's off-axis response, again related to the Schroeder frequency.  A speaker with reasonable on-axis response but poor off-axis response will sound better in a well treated room without a lot of reflections (reverb time), but a speaker with smooth on and off-axis response will sound better in any room, even those with typical living room HF reverb.  The speaker governs the general sound character in all rooms, the room is secondary from the Schroeder frequency and up as far as response goes, primary from the Schroeder frequency and down.  Even more importantly, in an untreated space, much smaller deviations in off-axis response become very audible.  In addition, increased directivity tends to improve focus and imaging.  Again, see the above cited Holman/Green paper. 
 
Room modes and reverb create a form of "distortion", but not the typical harmonic distortion found in nonlinear systems like speakers.  Speakers are often highly non-linear, especially when pushed towards Xmax.  Those distortion levels are often shockingly high.  There is no other component in the system that can generate 5-10% THD and get away with it.  
 
From years of measuring frequency response of turntables, cartridges and cables, I'm afraid I have to disagree that they are 1000x less than the speaker or room.  While uncorrected speaker/room response may be as much as +/- 10dB, a 6dB variation from (equalized) flat response is not unheard of in a phono system.  The combination of relatively high output impedance of a moving magnet cartridge and the capacitive and resistive load it drives makes for quite a bit of response variation from the idealized RIAA curve.  Fortunately, todays cartridges are less affected by loading than in decades past, and RIAA networks in preamps have gotten much more accurate.  But loading issues have not gone away by any means.  
 
The distortion of the groove-stylus contact is not small.  Well above 1%, often higher than 5%.  Go measure a test record.  
 
Yes, digital conversion and most analog electronics are non-factors in context of speakers, rooms and turntables.  
 
Nov 29, 2016 at 10:12 AM Post #12 of 29

watchnerd

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FWIW, my listening room is open on one side (the back), 17 feet x 12 feet x 8 feet.  If I recall the Schroeder frequency was in the low 200's.
 
There is no formal acoustic treatment, but it is carpeted, on top of concrete slab, few windows, bookshelves, a couple of plush couches.
 
Nov 29, 2016 at 3:37 PM Post #13 of 29

pinnahertz

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FWIW, my listening room is open on one side (the back), 17 feet x 12 feet x 8 feet.  If I recall the Schroeder frequency was in the low 200's.
 
There is no formal acoustic treatment, but it is carpeted, on top of concrete slab, few windows, bookshelves, a couple of plush couches.


All of that is acoustic treatment, if adventitious.
 
Nov 29, 2016 at 6:09 PM Post #14 of 29

watchnerd

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Dec 1, 2016 at 10:28 AM Post #15 of 29

gregorio

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  [1] The effect room acoustics has on frequency response - the "peaks and dips" referred to - do not occur throughout the audible band.  [2] Room modes affect lower frequencies only, and the point below which room modes become dominant is well known as the Schroeder frequency.   Below the Schroeder frequency room modes affect the total response (depending on location) because of room modes effect on discrete frequencies, [2a] above Schroeder, room modes overlap and become room reverb.  [3]  I've never measured a home listening room with a 40dB dip in response.  Ever. Sometimes there are greater than 10dB dips and peaks (20dB variation total) measured in a single location, a problem often cured with minor physical adjustment.  [3a] Pro studios do not have 10dB troughs unless they haven't been properly tuned.  While there are many of those rooms, again, the critical mix position can usually be smoothed out with a trap or two, or the use of multiple subwoofers that can be properly positioned.  In a mixing studio we tune for a relative small LP, the mix position.  In home theater, we tune for all seats with somewhat greater tolerance.
 
 [4] A good reference paper on this would be "First Results from a Large-Scale Measurement Program for Home Theaters" by Holman and Green, AES, November 2010.  Data was taken from measurements of over 500 rooms, multiple positions for each.  The average Schroeder frequency ended up around 200Hz, reverb time under .3 seconds.  
 
[5] Room modes and reverb create a form of "distortion", but not the typical harmonic distortion found in nonlinear systems like speakers.  Speakers are often highly non-linear, especially when pushed towards Xmax.  Those distortion levels are often shockingly high.  There is no other component in the system that can generate 5-10% THD and get away with it.  
 
[6] From years of measuring frequency response of turntables, cartridges and cables, I'm afraid I have to disagree that they are 1000x less than the speaker or room.  While uncorrected speaker/room response may be as much as +/- 10dB, a 6dB variation from (equalized) flat response is not unheard of in a phono system.  The combination of relatively high output impedance of a moving magnet cartridge and the capacitive and resistive load it drives makes for quite a bit of response variation from the idealized RIAA curve.  Fortunately, todays cartridges are less affected by loading than in decades past, and RIAA networks in preamps have gotten much more accurate.  But loading issues have not gone away by any means. The distortion of the groove-stylus contact is not small.  Well above 1%, often higher than 5%.  Go measure a test record.  
 
Yes, digital conversion and most analog electronics are non-factors in context of speakers, rooms and turntables.  

 
1. Maybe the all rooms I've measured are just freaks of nature but I've never seen or even heard of room which does not have very significant variation in FR response throughout the audible spectrum, with high res, non-smoothed RTA measurements from about 1kHz upwards typically resembling a seismograph during an earthquake!  Freqs at/below the Shroeder commonly consume much/most of the treatment budget in a studio build but we certainly never just ignore treatment well above the schroeder.
 
2. Your statement ("room modes affect lower freqs only") appears to contradict 2a? 2a. Agreed to an extent and even then, certainly not a flat/random reverb!
 
3. I did not say a 40dB dip in response, I said "peaks and troughs". Looking at the worst peak and worst trough, a 30-40dB variation between these two points is not only entirely common in my experience but something I've witnessed pretty much without exception in every untreated room I've ever measured. At the standard RTA resolution of 1/3 octave, I can't remember off the top of my head ever seeing anything quite so drastic but using a 1/6 or 1/12 8ve non-smoothed, to see more precisely what's going on, it's entirely common.
 
3a. Again, total variation between worst peaks and worst troughs at higher than 1/3 8ve resolution. Generally, there is at least 10dB between those points, even in world class studios! Pro studios are, as you mentioned, quite a different kettle of fish though. One obvious difference is a large reflective surface right in front of the LP (the mixing desk) and of course we can't solve this by just covering the desk with a trap or two (or with the use of additional subs)! Also, absorption panels (traps) are ineffective below about 80-100Hz, to treat the almost inevitable LF problems in any relatively small room requires treatment other than simple absorption traps; tuned panels, Helmholtz resonators, etc., treatments which are generally well beyond all but a tiny minority of the most extreme consumers.
 
4. Thanks, I'll try to look out for that paper but I've not been a member of the AES for quite a few years. That Shroeder freq tallies well with my experience but I'd be very surprised if the paper really concludes what you appear to be implying. Maybe I'm mis-reading but the implication I've understood from you post  is that room response above approximately 200Hz is largely inconsequential. This would fly in the face of standard pro studio design, where we always treat well beyond the Shroeder freq, typically not just (and sometimes not at all) with broad band absorption (traps) but also with various forms of diffusers, to randomise the interactions of higher room mode harmonics/reflections. Additionally, commercial studios are specifically constructed to avoid certain quite severe acoustic problems, problems which are often inherent (without treatment) to consumer listening environments. Flutter-echo being an obvious example.
 
5. I agree. I wasn't talking about what is the most audibly objectionable form of distortion though, just very significant measurable variations from flat, as opposed to the difficult to measure, let alone audible, distortion of say ADC jitter. Most consumers, even many/most audiophiles are blissfully unaware of their acoustic problems, even less so above their Shroeder freq but that doesn't mean the problems don't exist or aren't audible. Trained listeners, such as experienced pro audio engineers, would be aware of these problems (including those an octave or 3 above Shroeder!), and the consequences (when surgically EQ'ing for example).  I also wasn't speaking about extreme circumstances, pushing a system/speakers beyond their capabilities (towards Xmax for example), although I make no judgement about how common those extreme circumstances may be amongst consumers.
 
6. Unlike you, I have no experience of measuring turntables. I've never owned one myself and have only experienced other peoples'. In those cases, they were expensive well maintained units and while even the best turntables are obviously still susceptible to the deficiencies of vinyl (HF inaccuracies, etc.), I didn't realise the FR variation was generally as bad as you indicate.
 
If we consider that by the time we're 1m or so away from our speakers, what's hitting our ears is roughly a 50:50 balance of reflections vs direct sound, then acoustics is obviously a very major player and by two meters or more, easily the dominant player, at least as far as FR is concerned, if not conscious awareness. Certainly I've measured and heard $1k speakers in a well treated room which perform significantly better than speakers at pretty much any price in an average consumer's untreated room. I'm not really disagreeing with the principles you've mentioned, mainly just with degree and from my personal experience I would switch the positions between your #1 and #3. It's entirely possible/likely I was incorrect with my "degree"as far as turntables are concerned and of course we can come up with extreme examples which don't conform to my assertion that acoustics is the dominate factor of FR but I do stick to that assertion as generally true and that acoustics, speaker and turntable distortion is likely to add up to well over 1000x the distortion of a competent ADC.
 
Quote:
  There is no formal acoustic treatment, but it is carpeted, on top of concrete slab, few windows, bookshelves, a couple of plush couches.

 
A concrete slab is useful acoustically in terms of sheer mass but is otherwise a problem, due to it's reflective properties. A carpet is certainly hugely better than nothing, better still, a thick carpet with a thick underlay but so close to the concrete is only going to alleviate the concrete's problems in the higher freqs. Windows are particularly bad in their reflective properties. Bookshelves (filled with books) can act as diffusers, so directly behind the LP is the best place for them acoustically. Plush couches generally act like broad band absorbers and therefore useful in the roughly 100-800Hz region, depending on how big/many and where they're positioned. It's actually quite surprising how much acoustic treatment one can often get away with. For example, a couple of rugs, hung an inch or two off the wall at the main reflection points can produce a very marked/noticeable improvement in room acoustics, while often not being too objectionable as far as the wife is concerned, especially if you let her choose the rugs! Then again, I'm on my third wife, so maybe I catastrophically underestimate how objectionable they find it?!
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