Nice post. May I ask if you ever designed a test to measure reproduction of 'depth?'
In case what it means is not clear, its part of the stereo illusion wherein a perceived location in space between the speakers is more distant for some virtual sound source than the perceived distance of some other virtual sound source, say, two vocalists one standing a couple of feet in front and a bit to the side of the other vocalist.
So far as I can tell it has to do with precise virtual source localization in left/right imaging as a starting point. Then the perception of depth is given by audible cues such as increased room reverberation with increased listener distance from a virtual sound source, and also with air attenuation of high frequencies over distance.
Getting all that right as part of the stereo illusion seems to be something that can differentiate most reproduction systems. Only the very best systems seem to be able to produce a compelling illusion with all cues well intact, especially so when challenging source material is played.
There are some other things that would be interesting to measure as well, but those can be left for another time.
The problem people have is a problem that's divided audiologists for many decades .
A scientific apparatus made for organic human beings with different levels of hearing and brain patterns .
Every human being is unique with their own likes/dislikes due to personality being a factor in judging listening to music .
Ear shape and auditory nerve connections to the brain are involved but many people like tube second harmonic but notice D.Self isn't a "tube man " its no light thing that many prefer tube audio.
Even sitting in a concert hall you don't hear the top end if you are in the back row--acoustics are involved not a studio recording room that produces a reasonable flat response .
Our DNA is from the original hunter killers of food who had to have acute hearing --not now unless you live in the countryside permanently .
I can see the scientific argument ---"well get the electronics right and the rest is up to the listener" yet look at the variations in design over many decades and the preference for one make or another obviously not everybody is convinced by that statement as "one mans meat is another s poison".
At the end of the day its down to what makes you happy not what others think is "right for you " - listen to music and ----be happy .
Once you convince the audio world that one make /model be it SS or vacuum tube is "perfect " then arguments will cease but I will be long gone before that ever happens ( if ever ) .
A scientific apparatus made for organic human beings with different levels of hearing and brain patterns .
Every human being is unique with their own likes/dislikes due to personality being a factor in judging listening to music .
Ear shape and auditory nerve connections to the brain are involved but many people like tube second harmonic but notice D.Self isn't a "tube man " its no light thing that many prefer tube audio.
Even sitting in a concert hall you don't hear the top end if you are in the back row--acoustics are involved not a studio recording room that produces a reasonable flat response .
Our DNA is from the original hunter killers of food who had to have acute hearing --not now unless you live in the countryside permanently .
I can see the scientific argument ---"well get the electronics right and the rest is up to the listener" yet look at the variations in design over many decades and the preference for one make or another obviously not everybody is convinced by that statement as "one mans meat is another s poison".
At the end of the day its down to what makes you happy not what others think is "right for you " - listen to music and ----be happy .
Once you convince the audio world that one make /model be it SS or vacuum tube is "perfect " then arguments will cease but I will be long gone before that ever happens ( if ever ) .
I want a way to measure a system to make sure that it reproduces what was recorded, right down to accurate reproduction of sound field hitting the mics during recording. If you think about it, it doesn't have to be measured only at the speakers. It can be measured at each stage of a system, the power amp outputs, the dac or phono stage outputs. Digitize it all and tell me where in the system the stereo illusion corresponding to the live sound field hitting the stereo recording mics is getting screwed up along the way. In what way is it getting screwed up, stereo channel coherence, asymmetrical cross talk, lost reverb tails is dacs, etc.
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I agree entirely with Russell's comment here; moderate, balanced, and well put.
I do not feel that measurement is the complete picture of a sound system. It's important, but there are systems with good figures which sound ordinary. One suspects we are not measuring all the things we need to; and a large proportion of buyers are quite determined to hear the system before they part with their cash. I have never found a buyer who did not want a long listen before the sale, and this is only correct as the customer is always right, even when he is wrong.
It certainly does not credit when good engineers insist the figures are all they need. This does not work with any personal purchase; automobiles for example. People like to drive them first.
The issue of depth of perception is moot here. You can't measure it, but we all know tube amps are very good at imaging v. SS. But tubes have terrible figures, yet people won't buy anything else. Are they all crazy?
HD (high distortion)
I tend to agree when the distortion figures was obtained from the acoustic output. THD of amps is not linearly related to THD of acoustic output.
Yes, I have. I was able to see some correlation between higher order harmonic distortion products and depth. I think it was actually higher order harmonic products present as IM distortion.
I thought it might be IM products of harmonics above 20 kHz, that reappear below 20 kHz, but as long as loop gain is kept high until 20 kHz, these do not appear to be a problem. They were hard to get at with 1990s measurement systems, but I probably could today. The reason I that thought was because aliasing products of 1980's era CD players folded down into the audio band, and it certainly made those have flat depth of soundstage.
In fact, depth of soundstage is one of the main audible cues I use to know if my system has got "it". That is to say, good enough specs to give the audio performance I want. The singer should sound like she is standing over there with the drums behind her and piano slightly forward of the drums, on one side or the other. Not too many recordings allow this, because they almost all just use pan pots to arrange the stereo image.
These are all subtle cues of harmonic content and delay that distortion products can easily obscure, in my opinion. The electronics play a major role, especially the power amp, because it controls the speakers.
Step 1 is fixing the room. All early reflections (< 20ms) should be killed and late reflections diffused. I tell people to hang curtains or tapestries on the wall behind their speakers, and mostly full bookshelves behind. No coffee table between you and the speakers, but a stuffed ottoman is ok. You can't hear the original space if your listening space is dominant. The more nearfield you listen, the less important this is.
Step 2 is getting the best speakers. Some DIY'ers can do very good speakers, but I would only do DIY speakers after I had a great reference. Measuring speakers well is not easy or cheap, and the results are tricky to interpret. Off-axis waterfall plots and time-delay spectrometry, to look for and kill undesired resonances and comb-filtering.
Step 3 is the amp. (It used to be the source material, and for some, it still is.) I don't need a reference amp to design a good amp, because the specs are simpler to understand and measure.
Step 4 is the source, which is a media server or even Bluetooth 5. This part is easier than it used to be. Today's DACs are phenomenal. If you have a turntable, then move this up in front of amps. Cartridge/arm/table selection is huge for imaging and naturalness of sound.
Step 5 is the preamp, if you even have more than one source. Today's opamps are phenomenal and there is no need to do a discrete preamp, unless you just have an emotional need to build that.
That's a horse of a different color. Don't forget this is an op amp thread. You drag speakers into it, and we have no hope.I tend to agree when the distortion figures was obtained from the acoustic output. THD of amps is not linearly related to THD of acoustic output.
I moved to Tucson in August of 2011, hmm...should I take credit?! Just kidding, I was just in applications at the time and they didn't let me start making audio op amps until 2015.
Just wanted to say I'm honored by the high praise on our parts, and always look forward to hearing the feedback from this community when we release a new one.
We're a proud bunch in Tucson, holding on to our Burr-Brown heritage. In fact, we named the lab in our new facility here the Tom Brown Engineering Lab, so we don't forget our roots
op amps are a nightmare to find the right one.
I design low frequency usb scopes and need about 1mhz bandwidth and high input impedance and RRIO. By the time I had filtered out what I wanted there was one op amp that did the job !
Some good op amps had high input bias current which were useless without a pot to trim it out.
Then a 3mhz op amp is only 3mhz small signal. For full range voltage it needs to be high slew rate too.
I design low frequency usb scopes and need about 1mhz bandwidth and high input impedance and RRIO. By the time I had filtered out what I wanted there was one op amp that did the job !
Some good op amps had high input bias current which were useless without a pot to trim it out.
Then a 3mhz op amp is only 3mhz small signal. For full range voltage it needs to be high slew rate too.