MUSINGS: "Which measurements matter?" Importance of considering the complete audio chain. And a listen to room DSP filters...

Very busy these last few days so I thought let's address an interesting discussion question I've seen over the last while about measurements and audibility. Here's a forum comment from tapatrick over on Audiophile Style the other day:

I think you have done a good job in your blog post of covering all the relevant areas involved from music production to listening. And maybe the conversation is now concluded. If only everyone would acknowledge and respect each others 'intent' as you put it then there would be a lot less misunderstanding. I am none the wiser which measurements matter but I have to say I'm now clear that measuring and analysing equipment outside of listening leaves me cold. I will leave that to others more qualified but I will keep an eye on developments...

Hi tapatrick,

I appreciate the post. There is something you highlighted in the comment that I think is worth spending more time thinking about; this is of course about the question of measurements and how these correlate with subjective experience.

As per the blog post last time, I think it's important to remember that those 3 parts to audio - PRODUCTION, REPRODUCTION, and PERCEPTION - each will have a role to play when we conceptualize the question "Which measurements matter?" precisely because the measurements we can perform on the hardware can only inform us about that piece of REPRODUCTION gear, and not necessarily on the full "Audio Trinity".

As I said last time, I think we are blessed these days with very low distortions, controlled frequency response, low noise, minimal crosstalk, and minimal time-domain anomalies such that the majority of reasonably priced gear (I'm not talking about the cheapest of the cheap of course!) can already be said to "sound good" when used and set-up appropriately. Anomalies in measurements of distortion, noise, crosstalk, and frequency response, I believe are rather straight forward to correlate subjectively when high enough. The problem is I think that the majority of audiophiles are not doing their own measurements so have not had the opportunity to correlate the objective results and subjective audibility themselves; the only way to remedy this is with experience and that will require some work on your part rather than listen to opinions of others. Further compounding this is that the "high-end" Industry keeps telling us that there are all kinds of significantly audible differences that measurements cannot catch! I do not believe this is true in 2020 for most devices.

I know in a thread I came across recently, folks asked "Which measure correlates with soundstage?". A great question which leads us down the path of a complex perceptual phenomenon! Let's use that to consider the role of measurements and subjective impressions...

From start to finish, music recordings are a product of those three major parts above, therefore the answer to many questions will necessarily be much more complex. A concept like "soundstage" is not a phenomenon that is answerable by examining the REPRODUCTION components like the products we as consumers purchase in isolation. It's meaningless if you ever come across a review claiming "this $2000 cable will give you a bigger soundstage than that $100 one".

Instead we have to ask ourselves what are the elements we need to consider for a complex perceived phenomenon like the "soundstage". First, we must always remember the importance of the PRODUCTION side. Since any subjective quality one might experience must first be encoded in the source recording, soundstage quality must first be captured in the recording and production techniques. This should be no surprise and is in fact the topic of the 1981 John Atkinson article "The Stereo Image" when he wrote about various recording techniques like multi-mono stereo, binaural, Blumlein mic technique, and spaced omnis (does anyone write technical audiophile articles like that in mainstream magazines anymore!?). Here's a more recent discussion on Reddit about microphone positioning to create soundstage. These days, like it or not, recordings are often made close mic'ed and "dry" so they can be mixed to produce a soundstage artificially. Furthermore, digital tools can be used to adjust front-to-back depth; check out this article from Sound-on-Sound. As usual, "garbage in, garbage out" if the PRODUCTION is done poorly.

As for our PERCEPTION of soundstange, binaural hearing obviously requires that both our ears are working properly in order to provide the amplitude, frequency and temporal cues for the brain to decipher. For example, an important part of hearing acuity has to do with one's frequency response - have a look at an audiogram.

Here's one from a family member a number of years ago to check hearing about a year after a severe ear infection with fluid effusion behind one of the ear drums:

This is an example of a typical pure-tone audiogram used primarily as a screen of the speech frequency spectrum approximately defined as 500Hz to 4kHz, typically tested up to 8kHz. For reference, with "normal" hearing, threshold for kids can go up to 15-20dB, while for adults, it can be up to 25-30dB on the graph. By the time this audiogram was done, the infection was cleared and hearing was reported as subjectively back to "normal" by the individual.

As you can see, the "O" line represents the right ear, and the "X" is the left ear. If you've ever had your ears tested, you'll notice just like the graph above, typically our ears are not perfectly equivalent. In the graph above, the left ear overall is more sensitive than the right consistently by about 5dB or so (indeed the ear infection a year back affected the right ear more).

With the audiogram above clinically within "normal" limits, the family member is back to usual life including doing musical performances, and her brain/mind has obviously adjusted to the interaural discrepancy such that subjectively "everything sounds back to normal".

But here's the tough question worth thinking about... If this person were an audiophile (and I bet many audiophiles out there would have audiograms worse than this), would you have any reservations about this person's reporting of how he/she perceives the "soundstage" since we do need both ears to "work" well for "accurate" perception? What if this person were an audiophile and used phrases like she heard an "immersive soundstage", or that a pair of speakers sounded "effortless" or even more vague subjective words like "magical"? How would we determine whether this person provided an accurate testimonial (review) of what was heard? If this person were to apply as a "professional" to write for a well known audio magazine, what kind of criteria would be used to gauge this person's aptitude beyond being able to write in an entertaining manner and familiar with the audiophile lingo? Would a person with such an audiogram still be eligible as a "Golden Ear" deemed capable of differentiating cables and bitperfect audio streamers?

Unlike measurements of speakers where we can easily capture data over thousands of points and speak with some authority about concepts like high fidelity or "accuracy", the measurement of human hearing at least clinically is nowhere near that level of detail. I bet if we measured the hearing acuity of audiophiles, we would be able to point to a number of individuals where we can wonder "So Mr. Golden Ear Audiophile, are you sure you can hear a wider soundstage using this USB cable with that kind of audiogram as you claimed in that review!?"

We can calibrate our measurement devices to examine objective performance, but is the human "instrument" calibrated with adequate insight into his own hearing? As such, with what confidence then should we attribute to testimonials? For the "more objective" audiophiles, the answer does I think need to be one of healthy skepticism unless the person is a trained listener and can demonstrate listening skills.

Finally then, when it comes to REPRODUCTION equipment and a higher level phenomenon like "soundstage", then we have to think about whether the source device is "bit perfect" and distortion-free, whether the amplifier is accurate with precise channel balance, and if the speakers are likewise well-balanced across the audible spectrum, able to reproduce the dynamics without distortion, and have adequate time-domain performance (ideally precisely time-aligned). Furthermore, we do need to consider the room quality, plus choices made like how far apart the speakers are and details like tilt and toe-in appropriate for the device. Of course, the audiophile then should be seated in the "sweet spot". If we do all these things, then we will simply recover (REPRODUCE) the "soundstage" that was embedded in the PRODUTION, hopefully PERCEIVED with high quality ears and mind!

In summary... My experience has been that measurements correlate nicely with sound quality already once you appreciate and account for the production quality, have your gear and room reasonably sorted out, and appreciate the perceptual limitations of one's own ears and mind. As far as I can tell, the folks that disagree most with this are those attached to the audiophile Industry who seem to think there's still significant amounts of "magic" out of reach from measurement instruments (including null testers and software like Audio Diffmaker or Paul's excellent DeltaWave). This is how they justify unusual products and illogical claims while of course never providing evidence (often deferring to circular reasoning because the "right measurements" have not been discovered!).

[Speaking of evidence-less, unjustified products, consider this recent review of the UpTone EtherREGEN. By all means, evaluate the claims in this wordy white paper. May I humbly suggest that there are better ways to spend US$640 than on a rather odd ethernet switch which IMO cannot change the jitter of one's DAC output to any significant degree? I would suggest waiting for Mr. Swenson to release his measurements first ("I look forward to the measurements data to back up the claims, which Swenson says he will publish soon.") if you're still interested in pulling out the credit card. As far as I am aware, he never released measurements for his UpTone USB Regen despite statements to that effect years ago as I recall.]

Alas, as a hobbyist, the only way one could confirm what I say might be true is if you start doing your own measurements and experience the claim for yourself.

--------------------

The other night, it was great to have Mitch Barnett (mitchco) over to catch up on life, enjoy dinner together with our significant others, and of course listen to some music on the system!

As I had promised Le Concombre Masqué on the thread "Boundlessly abrasive offer to DSP work gratis" which I believe has been deleted from Audiophile Style, I would listen to some FIR filters he had created using his technique with rePhase using some sweeps created in my room using REW, and the miniDSP UMIK-1 microphone.

Here's what my speaker/room pink noise graph looked like spatially averaged using the Moving Mic Measurement (MMM), recorded from the main listening position with all the furniture in place:

As expected, a fair amount of room modes to be found in the lower frequencies below 300Hz.

I provided Le Concombre with 13 sweeps taken from around the sweet spot as shown here based on the Dirac Live 2 manual with additional data for further right and left:

Out of interest, here is the left channel frequency response from sweeps 1-9 which encompasses the "sweet spot" (or "main position") and the "box" about 12" on either side and 6" above and below the position.

Orange line = "sweet spot".

As you can see, moving the microphone around that main position within a 2-feet x 1-foot box results in significant changes (1/6 octave smoothing applied). While objectively obvious, I would suggest not getting too obsessed about the idea that moving speaker positioning 1" to one side or another suddenly makes massive change to the sound quality. I suppose if your speakers are really close to room boundaries, maybe moving 1" further out would have some audible effect, but let's not get too dramatic!

Thank you Le Concombre for creating two filters for me to try based on Harman RR and RR1 loudspeaker curves:

Listening to a few "audiophile" tracks like Stevie Ray Vaughn's "Tin Pan Alley" (Couldn't Stand The Weather), Patricia Barber's "Regular Pleasures" (Verse), and Yello's "Planet Dada" (By Yello: The Anthology) in Roon, it wasn't hard differentiating the sound from Le Concombre's two Harman curves compared to an Acourate FIR filter I made, and from one Mitch created using the same REW sweeps using Audiolense.

There's no point describing for you what I heard when I can show you the frequency response differences using a white noise signal averaged over about 30 seconds: [Subwoofer off.]

White noise. No DSP vs. My Acourate FIR vs. Le Concombre's RR curve vs. Mitch's Audiolense. Mitch tells me there was an issue with his Audiolense filter not importing my mic calibration properly so it could be significantly improved. 64k-point FFT.

I'll let you imagine the sonic differences as an exercise. Let's just say what Mitch and I heard using these filters were consistent with the graphs. Overall, I preferred the sound of my Acourate filter. Perhaps I'm just biased :-). Nonetheless, this was a nice demonstration of the power of DSP in changing the sonic character of one's system to taste. To me, subjective preferences play a role in which "house curve" I would choose.

Objectively and subjectively, clearly all of these filters improved the low frequency response. A song where one can hear this important improvement is the "classic" audiophile track by Rebecca Pidgeon "Spanish Harlem" (The Raven) - amplitude of the bass line should be relatively smooth and not bounce around when room correction is "tuned in".

Alright folks... That's all I have for now in the audio world.

Recent events around health care and the financial markets have been tumultuous and approaching life-changing proportions in many parts of the world. This means I've got to deal with things around here more important than audio as well :-). As a result, although I have some things I want to show you guys, I probably won't be able to update the blog as regularly until things settle down over the next number of weeks and maybe months...

Stay safe. Stay healthy. Remain rational. And above all, enjoy the music!

PS: Remember if you find yourself having time due to all the shut-downs and social distancing these days, give the Harmonic Distortion Blind Test a try! Still collecting data until end of April.