Misleading Measurements

[Bill Brown]

I read this thread at the beginning then stopped for a bit, catching up on the last 3 pages or so today.  I began thinking of some historical context.

 

In the very old days, mid-late 50's to the 60's as "Hi-Fi" blossomed, measurements came to rule supreme.  Some realized there wasn't full correlation of the measurements with sound quality and shifted towards a more subjective approach (JGH, who did do some basic measurements), HP, purely subjective, and the reviewers they published.

 

Then was then the phase of Stereo Review and Audio magazines.  In these measurements were dominant and we were told that products that measured well couldn't be differentiated in listening (and note the measuring systems were comparatively crude compared to what can be done today).  I do have to note the loudspeaker measurer at Audio who developed the TEF measurement system that advanced the art significantly, Richard C. Heyser.  This dedicated piece of test equipment could perform the array of time-energy-frequency (TEF) measurements based on his pioneering work on time delay spectrometry (TDS) for audio, perhaps the next major advance after the development of the Thiele-Small parameters.

 

This is the era that I entered the hobby, first with subscriptions to the above two, poring over the measurements and dreaming and buying equipment based on their data.  Then I was exposed to Stereophile and TAS and my evolution took off.  Before anyone decries these, please remember that they were the only sources available to us (aside from coming and going fringe sources).  Was this a normal/natural progression?  I think it was for me.  Surely it wasn't for all.  That is probably ok.  I suspect those folks are analogous to the current ASR types.

 

When JA became the editor at Stereophile it was very important to him to institute a measurement program with the stated intention of attempting to develop a body of measurements that would correlate with listening impressions.  He has expressed disappointment that this hasn't been as fruitful as he would like.  Certainly there remain massive questions/gaps in understanding, but there have been some good things.  The hypothesis of, then measurement of jitter (unknown as an issue in early digital products) would be one, further advances in loudspeaker measurement another.  I do think at this point that I am able to interpret to at least some degree correlation of subjective impressions with measurements.  It is certainly worthwhile to see measurements of products that seem poorly engineered in very basic aspects.

 

I drifted away from TAS at that point as I wished for measurements, believing that there would likely be measurements that correlated with the reviewers' subjective impressions, perhaps producing euphony (emphases in certain speaker frequencies, 2nd harmonic distortion, etc. as examples).

 

I am neither a radical subjectivist or objectivist.  I want to read both, and do.  Engineering advances guided by measurements are important.  Listening is important as I don't think measurements fully correlate with listening.  Too strong an emphasis on either isn't as interesting to me.  I occasionally skim through ASR just to see the measurements, but avoid the commentary, have no interest in the attitude, and don't have the site bookmarked by any stretch.

 

It is just a hobby.  There will always be all types, some that evolve in different directions, some that don't, oh well.  No need to fight about it.  I suppose in this respect, I disagree with your fundamental hypothesis, @The Computer Audiophile, just let them have their fun. 

 

Bill

[Bill Brown]

15 hours ago, The Computer Audiophile said:

No way!

 

Organic Nepali Golden Black

 

https://youngmountaintea.com/products/nepali-golden-black

 

:~)

 

Tea nerds?  I'll stick to coffee

 

Bill

[Bill Brown]

1 hour ago, Teresa said:

I drink both and prefer them black.

 

Agree!

 

In Texas our tea is iced, though I differ from lots and drink it unsweetened

[Bill Brown]

1 hour ago, opus101 said:

Grammar is analysis of words - text and speech have physical reality.

 

Definitely.  Otherwise a whole field of science isn't really science.  Thankfully our brains are very real, though admittedly, our understanding of it relative to other organs could still be described as fairly primitive. 

 

Bill

[Bill Brown]

My impression (I don't have sources, perhaps it was Earl Geddes) suggest that air is largely linear except at very high pressures (not at the levels our speakers can produce).  The discussions I have seen are in regard to compression drivers, but even there (huge pressures) I don't believe it is non-linear.

 

Bill

[Bill Brown]

16 hours ago, pkane2001 said:

With very large amplitude sound waves (extremely loud) the air becomes nonlinear. Even the air temperature can change locally due to high compression at the peaks of the waveform. Localized compression and temperature change result in faster sound wave propagation at the peaks than at the troughs, where the air gets rarefied  and cooler. The result is a distorted sine wave that might look more like sawtooth than sine.

 

Yes, but my emphasis is that this doesn't occur at our listening levels.  I feel fairly confident in that.

 

And yes, @bluesman, love the reference to the relevant physics, my first scientific love.

 

Bill

[Bill Brown]

On 4/27/2021 at 7:15 PM, stereo coffee said:

You only need to attenuate consumer line level,  which is NOT 2v RMS its nominal 0.316v RMS  , You might be reading too many reviews that test equipment at that high level, that is unrelated to what is at a RCA socket when playing CD's in home audio systems. 

 

Why its bad is because your source component contains the very best opportunity of presenting music as it actually can be, adding anything in-between other than resistance to attenuate,  simply detracts from that opportunity.    

 

I believe the initial standard for the output of CD players was 2V.

 

Really, all of this comes down to proper gain-staging rather than any standards, i.e. the lowest gain that drives your amplifier to full output, such that you minimize attenuation in preceding components, either analog or digital.  Significant gain in a preamp that is only subsequently attenuated is suboptimal at best.

 

My DAC outputs at the professional standard.  My amplifier on its lowest gain setting (which minimizes noise, the goal of all of this) typically leads to -5 to -12 dbs of total system attenuation, loud listening it is close to 0 (if our listening was only at one level this would allow and be the ideal scenario).

 

Bill

[Bill Brown]

This is getting bizarre, heck, borderline ridiculous.  @March Audio and @bluesman are absolutely correct.

 

There is a conversion of an analog signal to digital (ADC).  You CANNOT encode a music signal with one and zeroes above 0 dbFS, it will all be (terrible) noise, there is no headroom recording digitally.  In fact, you should not approach 0 dbFS, as they said, to avoid intersample overs when the ones and zeroes are converted back to analog (DAC).

 

When a DAC chip converts the digital signal back to analog (in a DAC designed for pros or consumers), it produces either a signal that could be described as current or voltage.  If the former, a current to voltage converter is the next stage (traditional), in the latter, this is done on the chip (modern).  This voltage then goes through additional gain stages in the DAC to either produce -10dbV from consumer DACs (typically, but not always), or +4dbU in professional DACs (more closely adhered to).  These levels are important to interface with subsequent/corresponding consumer or professional gear that is designed to accept the different levels for proper gainstaging (enough to drive to full output levels in preamps, then amps, but not overload them).  It really isn't complicated.

 

Bill

[Bill Brown]

1 hour ago, March Audio said:

This voltage then goes through additional gain stages in the DAC to either produce -10dbV from consumer DACs (typically, but not always)

 

Yes, my mistake, you are correct.  Sorry.  2V is typical (what I meant to write first and noted before instead referencing the standards, oy), but there is more variation than seen in professional DACs.

 

Bill