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In Reply to: RE: Have you posted by fmak on October 6, 2011 at 22:09:02
Is search for previously posted methods (me and others) and see if I can refer to them. Plus I need to check it for accuracy up to and including XP. Then I would need some volunteers to repeat said tests under Vista/Win7 to confirm behavior of WASAPI.
The test works well for digital outs (SPDIF, AES/EBU, USB and likely firewire devices as well). Any change to the bit accuracy of the DTS encoded test track scrambles the info the decoder needs at the other end. There is the trick - you need to send you data into a device which can decode DTS streams. It's not a valid or practical test for ALL applications, but when it's usable, it's always definitive and makes bitperfect troubleshooting in real time a breeze. When you are bitperfect, you get music. When you're not you get thissssssssssss. And you can actually get digital mixing to engage/disengage DURING playback and begin to make real corollary between things that affect bitperfect playback and things that dont - for EACH type of output you want to use or test. I wish I made a proper test report... I believe it's time to repeat this whole experiment, and on different OS as well.
I still use XP because I have drivers for all the hardware I have here, it works without hiccup, the OS is stripped down for dedicated audio usage, and I think I get fantastic sound where the OS is not the weakest link (hardware is now where I think I can get the most benefit from upgrade).
I really need to find the originator(s) of this test and give him/them proper accreditation for this fantastic idea.
The two most important items one must have are:
1. A means of ascertaining the actual speed the sound card is outputting.
2. A means of verifying (when this speed matches the sample rate of a file) that the output to the DAC matches bit for bit the content of the file.
There is little or no point in doing any further optimizations until one if confident that the music we purchased (possibly as modified deliberately by us) is actually reaching the DAC. Of course, once this has been achieved there is still the question of getting good sound because of more subtle and difficult problems, e.g. jitter and electrical noise. But if the wrong bits are getting out this is hardly important.
There are basically only two ways of getting the right bits out: trust or verify. Given the immense complexity and lack of transparency of all the software in a modern PC, (no matter what the type) and the track record of numerous vendors, IMO "trust" is an absurd concept. One is left, therefore with "verify".
In some (rare) circumstances, I've had resampling situations that actually resulted in a PITCH CHANGE. How noticeable is a pitch change from 44.1 to 48 or 48 to 44.1? On unfamiliar material, it might go by unnoticed! (This is what, like a "half" semi-tone in pitch change??)
So another test would be to play 44.1 and 88.2 of the same material to make double-sure there is no pitch change going on.
With DTS passthrough test, though, ANY resampling or ANY volume bit change (any change at all, then) will result in thissssssssssss.
It's a good test! And I've tested the test too... :P
You're right, but I would add:
-Verify using a proven test method
Yeah, proven test method for sure. But I'm not sure how to explain this to people, because if one gets a magic "test box" that says "pass" or "fail" then one ends up having to trust this box. Or trust some inmate that his "proven" method actually works. :-)
Switching between 44.1 and 48.1 amounts to 8 percent, a little more than a half step (e.g. C to c#). Nearly all music lovers will hear this in an immediate comparison but only a minority (those with perfect pitch) are likely to notice this error in isolation. It's much less of a "ha-ha" than running a 45 vs. 33 1/3.
In the past I've managed to trick my system into making gross errors, e.g. 88.2 vs. 44.1. This goes beyond subtle or annoying and enters into the amusing category. (So far it has happened only when I was already trying to "trick" my system, otherwise it would definitely have been annoying.)
Yes. Half a note!
But from 44.1 to 88.2 or 96 anyone should be able to hear the chipmunks.
I work as a technologist in electrical engineering. We're always required to prove "black box" mathmatical models or algorithms with alternate calculations.
Too much "hey we got an answer, wonderful" in some areas.
And G.I.G.O. still applies too...
My dCS972 tells me all that. Even shows bit activity.
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