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In Reply to: nonsense posted by bwaslo on March 3, 2007 at 15:55:46:
Bwaslo, you should have more experience before commenting.
First, sound cards DO effect the sound. IF they didn't, we would pronounce them perfect and not go any further. It would mean that if I added the AD-DA converter that I purchased for less than $200 on sale, from Leo's Music, a pro audio outlet, in series with my preamp, that it would be perfectly inaudible. We have found that this sort of thing IS audible.
Next, you act as if we think that all the subtle changes that we make in audio can be made obvious to everyone, everywhere, with cost effective audio equipment. No it can't, BUT we can detect differences in our own equipment that we have become used to, with audio sources that we know are recorded to a very high standard of quality.Technically, this difference test, while potentially being an important tool, will suffer from the limitations of the sound card. Perhaps, not as much as normally, because some of the more obvious harmonic and IM distortion will be cancelled out, that was generated by the op amps before and after the A-D processor, but the noise will still be added and will be at least 3 dB higher than the wire as it would normally be evaluated. This is because the subtraction of the coherent parts of the signal will not cancel the random effects of the noise from both samples taken. In effect, I would think that I would see mostly noise in the error signal. Another big problem is phase differences at both low and high frequencies. This might not be too much of a problem with a wire, but a component (such as a cap) would seriously suffer differences with another component.
It would seem that only the simplest things, like a wire, could be tested easily with this device without linear distortion adding and confusing the error output.
Another really important factor is the OMISSION of information caused the the sound card. If the sound card was so good in the first place, would it omit infomation? Listening tells me that it does do just that. If you omit information, how do you get it back, to see how it has been changed?
It should be noted that we have been trying to do this sort of thing for decades. We did it with 10 bits and a 50KHz clock rate, 1/3 of a century ago. We could not see any significant differences in good (Levinson JC-2 level) op amps, and I have always wanted even more resolution like 16 or even 24bits, but like Jon Risch, I doubt that it will be very effective. However, it would be a Godsend for us, IF it really worked.
Follow Ups:
John,I am quite well informed on this, I think, thanks. I bet I've tested and listened to many more sound cards than anyone reading this forum. I fight problems in (some of) them way too often, if fact. I read the disagreements, here, but they don't seem to hold water to me. Let me try to spell out why.
"First, sound cards DO effect the sound. IF they didn't, we would pronounce them perfect and not go any further"
Guys, just where did I say that sound cards don't affect the sound? I admit I'm not the best writer, but I know didn't write that, not ever. In fact I test soundcards regularly and have a pretty good idea what most can and can't do. OK, soundcards can and do affect the sound. There!
But, SO WHAT? So does every loudspeaker ever made. Yet, somehow, amazing as it is, people hear differences in equipment while listening through loudspeakers! Same with some amplifiers that can affect the sound. And the sound being changed was recorded with mics that affected the sound, too. Clearly these don't automatically invalidate testing, then, so why do they invalidate a differencing test?
Yet again: the soundcard CAN vary the sound, and still be quite usable, just as can the the incredibly imperfect loudspeakers we all use in domestic listening rooms. For the differencing test, the soundcard only has to respond to the difference, not reproduce it verbatim.
Yours and Jon's argument seems to be (correct me if my understanding is wrong) that:
(1) one can never detect a difference, even with mathematical processing, between two signals recorded with soundcards. Because the soundcards can affect the sound. Yet,
(2) a listener *can* regularly detect such differences, by ear. Even if a number of the components he listens through affect the sound, too. Even if they affect the sound more obviously than a soundcard does. Even if that listener is a constantly changing organism every minute, with changing moods, states of hunger, thirst, tiredness, age, etc. , never exactly the same for any two tests.
Can't you see why I disagree? Can the argument of "not enough resolution" be valid in the one case, yet not in the other?I can rather easily make two recordings with an intentional inaudible difference, (inaudible to me, of course, who knows about others!) which difference can be exposed and made audible by the software. But I'd like to find situations where there are recordings that have differences that ARE said to be audible and can ALSO be exposed -- revealing the reported difference for more listeners -- by differencing. Now, surely, having that difference be audible can't automatically make it even MORE difficult to detect via differencing, could it??? The program can make something that is inaudible audible, it is not hard to do that. It doesn't seem to me to be much of a stretch to think that it could also render something that is audible to some (but not to others) more audible, and reduce disagreement about the situation.
Note that I have also not said that every difference can be resolved by this using any equipment. I sense people think I'm trying to prove nothing is audible unless it can be measured. I'm not. I don't care much about proving something that can't be proven like that. I'm only trying to make audible differences, if they exist, more obviously audible by removing the other program material that can mask them. If someone as a result finds that a differencing convinces them there is no relevant difference between two things they test, based on what they hear (or don't hear) themselves with their own ears, that will be their conclusion (which they are free to make).
Obviously, if a differencing test were made through a telephone, the difference test would leave (at least) obvious noise, and no conclusion could be made. But it wouldn't leave silence. There might be signal behind that noise, but not apparent SILENCE altogether. So that just becomes a simple case of inadequate equipment or setup for the test. That can easily be checked with a dummy test. We can all agree that the test can't be useful in all cases. But I think it can be useful in very many cases. Particularly useful, I think, is the characteristic that lets people evaluate audibility more readily using their ears to hear the difference recording, without feeling challenged or being unduly influenced by expectations in either direction. But I see that some here do not agree. Que Sera.
"the noise will still be added and will be at least 3 dB higher"
Yes, noise will increase 3dB, but if the 3dB increased noise is not heard, I submit that it doesn't matter. The noise is always there, and it is always 3dB higher than some other level. (Anyway, even if it did matter, it wouldn't be hard to eliminate the 3dB increase: the tests could be recorded twice for each case and each recording set for a case averaged coherently. That would reduce noise by 3dB again, back to even. We could even average more than two for each situation and *reduce* the overall noise if we wanted to!).
"Another really important factor is the OMISSION of information caused the the sound card. If the sound card was so good in the first place, would it omit infomation? Listening tells me that it does do just that."
John, you are aware that such omission is in terms of your mind's rediuced ability to extract meaning and impressions from a signal that now less resembles the original signal you can relate to. We don't hear with spectrum analyzers. We can't hear degraded hash as well as we can notice degraded music. Information is a matter of context. But subtraction is not a matter of context or affected by masking (it has that very significant advantage over traditional listening tests for difference). The missing information is not from some buried signal completely vanishing from the larger signal with no effect, how could it *possibly* do that??
"Another big problem is phase differences at both low and high frequencies. This might not be too much of a problem with a wire, but a component (such as a cap) would seriously suffer differences with another component."
That is true, agreed (and experienced). Very small mismatches leave rather large difference results, the amount is easy to calculate, infact (see the Help file of the program). But that only means that care must be taken to handle these KNOWN effects. I've done such a test with capacitors, which of course make a first order filter (hp or lp, depending) in combination with the source and load resistances. It is a simple matter of adding resistances (or extra capacitance) to match the rolloff characteristics; at line levels, a 10 turn trim pot in shunt somewhere has done well. There is even a simple response analyzer system built into DiffMaker to help in adjusting these. What if the caps aren't matched well enough? Then, it will show up as an existing difference (which it is). Might not some characteristic of that trimpot cause an audible difference? Maybe, but if so, that will show as a difference, too. But, clearly (to me, anyway) neither has ANY way to show a false null. Mistakes make differences, not nulls. Presumably interesting difference results will result in further exploration to detect whether we are getting fooled by such things.
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There are some comments in this forum that the DiffMaker test suffers from the same objections as do ABX tests: that the hardware used for the test can invalidate the result due to lack of transparency. I submit that is just not so. Hardware might degrade signals, so that they become less easy for a human to relate to, because they sound less like something humans care about (music). That might be a factor with human listeners involved with music during ABX. But after differencing, the listening is only for absense or presence of remaining signal, the main common signal is gone. The hardware simply doesn't know what part of the signal it sees is the original music and what is from the change made by the cable/tweak/etc. It's all just "signal" to it, one thing. I'm surprised that that, at least doesn't seem obvious to others here. Hardware must treat all parts of the signal about the same, it has no way to selectively strip one part off, based on how it got there, so that effects of the change completely go away.
....and sheesh, I'm tired of writing about this. Good night, all.
I think that what Bwalso is saying that regardless of the measuring ABILITY of the soundcard, it is still a valid CONTROL, since we're using the same soundcard for both tests.If you have mediocre speakers but can hear an improvement when you change sources - agreed - it must be QUITE a significant improvement. The trick was that you used the same speakers to audition BOTH sources.
It's a no brainer that one would want to have the lowest noise floor possible to see even the most minute differences.
There is also a difference bewteen the dynamic range and SNR ratings of a codec ON a soundcard and what the actual SNR will be when a loop-back noise-floor test is done.
I also imagine one can't do bit-for-bit comparisons unless the stimulus is synced with the recording equipment for each iteration. Is this correct?
Once again, I applaud your effort in making this program. It is possible that it will supplant linear subtraction in many cases, such as the setup that Walt Jung and I used to measure caps more than 20 years ago. However, I think that comparing wires will be difficult with this test, but that does not show that wires have no sonic difference between them. That has not been my experience, and since I don't make wires, I would prefer that all 'well engineered' wires sounded the same. It would save me a good deal of time and effort, in making my products.
The bottom line is the resolvability of the AD-DA converters and their attendant circuitry, which seems to remove too much low level information, and this would not necessarily be made audible by cancelling out the main signal. It would seem to me that you are looking at differences residing at the 1 or 2 bit level in many cases.
Perhaps I am wrong. What differences have you found between common components with this test?
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