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Those of you who believe measurements aren't the whole story, do you have a hypothesis why that is?

DonH56

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Q-sound proves stereo speakers can fool our brain. It can image objects behind or well beside you over two channels only.

Now that doesn't mean all imaging is an illusion. Our normal hearing in the real world is capable of letting us pinpoint where something is with pretty good precision. The main factors in this ability are used by normal stereo to help us hear what is an audio illusion. We hear sound coming from a position where there is no sound source.

Imaging is an illusion but, if it can be elicited by a determined set of stimuli, they are the measurable element(s).

Good example.

No, I never imply you are ignorant, I know where you are coming from. You believe that since this is something we can hear, can feel, there must be something causing it and we can measure that something...

Yes, you can indirectly measure spatial effects. Since you can edit EQ and create it, you can alter it. You can increase or reduce these effects. You can measure what you have changed in order to create an increase/decrease in these effects.

The problem lies in quantifying this effect. There is no way to quantify this effect objectively. You cannot measure it (like measuring loudness or frequency). You can only assign a subjective number, eg. level 1 - 10. This is essentially same as blind testing. Having said that, it is still possible to at least somehow quantify it. One method I can think of is to use an approach similar to Scoville Heat Units (SHU).

Those EQ settings, we can break it down into minute steps and quantify it (eg. 1 spatial unit or perhaps SPU). We can do a blind test to determine how many times we need to increase before the sample group can detect a change in the spatial effect. I believe we can see a pattern emerging.

Lastly, perhaps you could suggest some answers instead of just questioning. To date, no one has tried to measure spatial qualities and quantify it. Perhaps you could start.

To address the very last response first, if nothing else, this thread proves I am not competent to suggest any answers!

As @escksu pointed out, my experience in other areas of signal processing is apparently inappropriate to how we process audio signals. @Blumlein 88's response is a perfect example of where my previous experience is fouling me up. With a radar system, I can create a signal where there is none there by adjusting the parameters of the source, such as amplitude and phase information over frequency. Or I can move around a real source so it is coming from a different place and at a different rate. What I do, and what comes out the radar dish and into the receiver, is all deterministic and measurable. EW (electronic warfare) systems do this all the time, and even without intentional misdirection other things like multipath and ground or sea bounce can create false images.

My apparent mistake was in thinking the same process was applied to audio signals, such that the position of an image could be determined from the signal sent from the speakers (or rather, reaching the ears, which is more difficult to measure). I can (and have) certainly adjust the signals to the speakers to move a source around, including moving it outside the boundaries of the speakers themselves, using an acoustic rather than radar processor. I did that long ago using bucket-brigade devices for a true time delay plus the usual analog circuitry to manipulate amplitude, phase, frequency response, and so forth. It was a fun project, presented for younger kids who were wowed by how we could move the sound around, but apparently inapplicable to this discussion. If the brain (processor) is making decisions based on (unknown to me) data then my basic premise (hypothesis) is wrong. Thus at this point I think my fundamental premise about what this thread is about and how we perceive spatial sound fields is wrong, and I do not want to waste more time (yours or mine). In this I am indeed ignorant, and following to learn.
 

NTK

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This is an example of the length and the complexity researchers (in this case, David Griesinger) have gone through to try finding ways to quantify spatial impression of reproduced sound. The example is on the measurement of envelopment:
(Quoted from: http://www.davidgriesinger.com/overvw1.pdf pages 7-8)

... Using this algorithm and a narrow band noise signal as a test probe we developed our measure for envelopment in small rooms. We call it the DFT, or diffuse field transfer function.
The process of finding the diffuse field transfer function can be summarized:
  1. Calculate (or measure) separate binaural impulse responses for each loudspeaker position to a particular listener position. A high sample rate must be chosen to maintain timing accuracy. In our experiments 176400Hz is an adequate sample rate.
  2. Low-pass filter each impulse response and resample at 11025Hz, and then do it again, ending with a sample rate of 2756Hz. This sample rate is adequate for the frequencies of interest, and low enough that the convolutions do not take too much time.
  3. Create a test signals from independent filtered noise signals. Various frequencies and bandwidths can be tried, depending on the correlation time of the musical signal of interest.
  4. Convolve each binaural impulse response with a different band filtered noise signal, and sum the resulting convolutions to derive the pressure at each ear.
  5. Extract the ITD from the two ear signals by comparing the positive zero-crossing time of each cycle.
  6. Average the ITDs thus extracted to find the running average ITD. The averaging process weights each ITD by the instantaneous pressure amplitude. In other words, ITDs where the amplitudes at the two ears is high count more strongly in the average than ITDs where the amplitude is low.
  7. Sum the running average ITD and divide by the length to find the average ITD and the apparent azimuth of the sound source.
  8. Subtract the average value from the running average ITD to extract the interaural fluctuations.
  9. Filter the result with a 3Hz to 17Hz bandpass filter to find the fluctuations that produce envelopment.
  10. Measure the strength of these fluctuations by finding the average absolute value of the fluctuations. The number which results is the Diffuse Field Transfer function, or DFT.
  11. Measure the DFT as a function of the receiver position in the room under test.
 

Digital_Thor

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ou


Put your speaker outside far from the wall and listen your stereo imaging ?

Atonio Fischetti (acoustician) the stereo picture is created by small movements of the unconscious heads. (in Initiation à l'acoustique)
Oliver Sacks (neurologist) the stereo picture is created by small movements of the unconscious heads. (in Musicolphilia)
So, how do we perceive stereo with headphones?
 

Raindog123

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Thus at this point I think my fundamental premise about what this thread is about and how we perceive spatial sound fields is wrong, and I do not want to waste more time (yours or mine). In this I am indeed ignorant, and following to learn.


I think you’re selling yourself short and giving up [on your radar based DSP experience] too soon. :) Both domains - RF and consumer audio acoustics - are governed by very same physics and math laws. And very similar [signal processing] tricks are often applied to both. And thinking that a human brain as an audio signal processor has some additional “magic” properties compared to DSP algorithms (whether on a GPP, FPGA, GPU, anamorphic chip; or often a combination of those), and that [two] human ears are somehow “mysterious“ compared to man-made sensors/receivers… is just silly.

Yes, there is often difference in topology - a stereo reproduction of recorded music is not the same as a “simple” radar illuminating the target and processing its reflection… Yet this stereo playback is not the same as, eg, a live “point source” acoustic instrument on stage, which in turn is not the same as a live instrument on stage through concert speakers… And I do not know about your experience, but what about bistatic and [coherent] multistatic radars? DF (direction finding) systems of all kinds? MIMO (multiple input/output) systems? Combined, used by by modern EW platform-protection systems to create “ghost” images to fool bad-guys‘ radars… The latter is virtually the same as the audio soundstage in question. (While again, none of it would work without very precise algorithms/measurements/processing. Yet it has no black-magic or voodoo “subjectivism” in it.)
 
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Robin L

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When listening to headphones, where do you feel the sound comes from? Inside your head? You don't think that is wrong?
Not really. Happens all the time when the stereo's off.
 
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Andrew s

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And thinking that a human brain as an audio signal processor has some additional “magic” properties compared to DSP algorithms (whether on a GPP, FPGA, GPU, anamorphic chip; or often a combination of those), … is just silly.
If you remove the word " magic" from the quote can you point to any scientific support for your assertion on how the brain processes audio is limited in the way you propose?
Regards Andrew
 

Digital_Thor

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When listening to headphones, where do you feel the sound comes from? Inside your head? You don't think that is wrong?
Not wrong... just different. Of course the sound changes when we "remove" the room. But no - I have never heard of stereo being a result of moving our head - and I have never heard of the terms "weak" or "poor" stereo either.
 

Robin L

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Not wrong... just different. Of course the sound changes when we "remove" the room. But no - I have never heard of stereo being a result of moving our head . . .
I've read [many years ago] about testing for stereo with the head set so that the small movements didn't happen, with a reduction in stereo imaging. I think phase effects are more audible with the small head motions, certainly I notice major differences in sound from a harpsichord [not a recording, but the real thing] from very small [like a 1/2 inch] movements. Try miking a harpsichord in stereo sometime, you're in for a thrill.
. . . and I have never heard of the terms "weak" or "poor" stereo either.
Plenty of those in the realm of early stereo classical recordings, like the Sir Thomas Beecham/Royal Philharmonic middle-side recordings for EMI in the late 1950's.
 

Raindog123

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If you remove the word " magic" from the quote can you point to any scientific support for your assertion on how the brain processes audio is limited in the way you propose?


My “assertion” is actually that man-made complex sensor systems (RF and acoustic) process signals similarly to human brain. Nowhere I‘ve implied the limitation of brain’s processing. The proof of this similarity is, eg, through performance comparison. Eg, of BBN’s Boomerang [compared to best bodyguards].

And if you‘re asserting brain‘s superiority, I‘ll leave the burden of proving that to you. :)
 

Andrew s

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My “assertion” is actually that man-made complex sensor systems (RF and acoustic) process signals similarly to human brain.
I am making no assertions just looking for proof of yours. Your link is unrelated to hifi audio and similarity of performance is no guide to how something operates.
Regards Andrew
 

Digital_Thor

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I've read [many years ago] about testing for stereo with the head set so that the small movements didn't happen, with a reduction in stereo imaging. I think phase effects are more audible with the small head motions, certainly I notice major differences in sound from a harpsichord [not a recording, but the real thing] from very small [like a 1/2 inch] movements. Try miking a harpsichord in stereo sometime, you're in for a thrill.

Plenty of those in the realm of early stereo classical recordings, like the Som middle-side recordings for EMI in the late 1950's.
Thank you - I'll look into that :)
Some of the oldest music I listen to, is Doris Day, which to me sound great - even in mono:

I hear the sound change ever so slightly when moving my head around a bit, but not at all problematic or something that I worry about in comparison with so much else, like bass, distortion and digital clipping in bad recordings.
 

valerianf

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To me testing audio equipment is not different than testing a car.
First you need metrics, what Amir is providing to us.
From there you need a team of professional drivers that will push the car to the limits and give their feedbacks.
It is where a long listening session is needed.
For audio this is far more difficult to find: on line and printed reviews are biased by advertising.
Nowadays nobody takes the time to do a long listening session properly, with 2 speakers and several "golden ears".
Worse, as corner audio shops have disappeared, you cannot do the listening session yourself.

Only solution is to read this forum and others, make a synthesis, order on line and return the item if not satisfied.
It is difficult for large and heavy items.
 

Raindog123

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I am making no assertions just looking for proof of yours. Your link is unrelated to hifi audio and similarity of performance is no guide to how something operates.


Whatever your say. Glad you’ve at least corrected your “your link is not related to audio” to “hifi audio”, as stating that an audio gun-fire detector is not related to audio is plain silly, no? :) Still, is there a point?
 

Andrew s

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Whatever your say. Glad you’ve at least corrected your “your link is not related to audio” to “hifi audio”, as stating that an audio gun-fire detector is not related to audio is plain silly, no? :) Still, is there a point?
Indeed it would have been that's why I changed it.

My point is that you assert (as far as I understand you correctly) that the brain processes audio the way our current DSP and related technology does. I see no evidence for this in the reading I have done on hearing and the brain.

If you have a reference that does provide evidence that it does I would love to read it.

Regards Andrew
 

aslan7

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Many people don't care about measurements and audio science because they like distortion. This is certainly the case with tube enthusiasts. They don't care about replicating the authentic sound and may even find that disagreeable as both an objective and actuality. Additionally, they have an emotional attachment to the esoteric paraphernalia they employ, vintage tubes, tonearms, turntables, cartridges, etc (really a variety of audiophile necrophilia). In short, plenty of people really enjoy distorted sound and couldn't care less about science. They like what they hear, plain and simple, and don't wish to be bothered by graphs, diagrams, Amir, etc. I don't pass judgment on them but do get annoyed when they criticize Class D and all the wonderful advances of modern audio like Purifi that sound amazing (and have a ton of power without weighing 50 lbs.). Some people like bad wine, so who is to judge them if they are enjoying themselves?
 
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