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My tests over kmixer effects, Seem to be none...
KikeG
post Jan 16 2003, 09:40
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I've been doing some tests over kmixer effect, both using standard waveout and directsound, connecting my TBSC digital output to my Audiophile digital input, under WinXP (no SP1), and I'm sure that with a single stream at 48 KHz, with the TBSC mixer volume at max, the kmixer doesn't touch a bit of the audio stream, it's sent bit-perfectly to the output of the card. At 44.1 KHz I can't be so conclusive, since the TBSC resamples everything to 48 KHz and I've had some problems to test it the same way, but according to my analog measurements in loopback mode of Audiophile output, there is no trace of signal degradation over the 44.1 KHz played data.

...So it's very possible that this kmixer sounding worse than ASIO or k.streaming is our old friend mr. placebo entering into scene again. wink.gif

Anyway, I'll do some more tests in the future.

This post has been edited by KikeG: Jan 16 2003, 09:42
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KikeG
post Jun 30 2003, 13:03
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Group: Developer
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Member No.: 137



Well, a couple of months ago I managed to get mi CMI8738 based card digital input to work.

Using it, and bit-perfect recording the digital output of my Audiophile card at 44.1 KHz mode, I've been able to verify that kmixer indeed does something to the data passed to it. The change is very subtle, so it was not detectable on my analog measurements of the soundcard output. What I've verified that kmixer does to 16-bit audio data, is just mangle the last bit of the data. It does like some kind of re-dithering of the signal, adding a very little amount of spectrally uniform noise to the signal, so that it is no longer bit-perfect. It also adds a very little amount (around -120 dB amplitude) of distortion that can be considered negligible.

I have measured this noise but I don't have the results at hand right now, but with this noise added, the dynamic range of the 16-bit signal is still better than 90 dB.

I haven't been able to do same tests with 24-bit audio, because I can't get a 24-bit recorded data, but I think this is a problem of my testing configuration, because on analog measurements, the analog output of the card with kmixer processing was able to produce an analog signal with better dynamic range than the possible with 16-bit audio. I'm trying to fix this.

When using kernel streaming and ASIO, the output is bit-perfect in 16-bit mode, as it was supposed. There's some evidence that using directsound acceleration (also called hardware mixing) does same thing as using kernel streaming, and enables getting bit-perfect output. However, I haven't been able to verify this, since my Audiophile card doesn't support it.

Note that when kmixer is acting and you play 44.1 KHz data, it can do do two different things depending on the driver implementation. The first is just this relatively bening bit mangling I've talked about in this post. But on some cards and modes (wave output instead of directsound, for example), it will resample the signal to 48 KHz, and this is a greater change to the signal. I haven't done very detailed tests over this resampling, but it worsens a little bit more the SNR of the signal, causes some low-level distortion and causes a very slight HF rollof. At first I don't think this is audible under usual listening conditions, but I haven't done any listening tests.

Note also that there are some professional-oriented cards that use special WDM drivers that don't suffer from any of those kmixer issues. These drivers don't fully conform to the WDM standard, and can't use kernel streaming, but, on the other side, they don't need it. RME cards for example, use this kind of non-standard, kmixer-free, WDM drivers.
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- KikeG   My tests over kmixer effects   Jan 16 2003, 09:40
- - thomaspf   Could you describe this setup in a bit more detail...   Jan 16 2003, 20:02
- - KikeG   I used WinXP pre-SP1. As I said, at 48 KHz, I use...   Jan 17 2003, 09:46
- - kaiwei   Did anyone actually claimed that it sounds better?...   Jan 17 2003, 11:52
- - KikeG   I don't think anybody has claimed it sounds be...   Jan 17 2003, 12:06
- - dev0   So basically all of thomaspf claims turn out to be...   Jan 17 2003, 16:17
- - thomaspf   Very interesting. All the experiments I did came a...   Jan 17 2003, 17:17
- - Pio2001   Loopbacking a soundcard into itself can lead to pr...   Jan 17 2003, 18:43
- - thomaspf   Interesting. I thought input and output of this ca...   Jan 17 2003, 19:21
- - KikeG   thomaspf, there's one thing I don't unders...   Jan 18 2003, 17:59
- - thomaspf   Strange. I have an M-audio DIO24/96 and I have no ...   Jan 19 2003, 06:11
- - Pio2001   Actually, long ago, I managed the same loopback wi...   Jan 19 2003, 14:51
- - thomaspf   Windows has supported a various driver models over...   Jan 19 2003, 18:03
- - thomaspf   A few more results. First I recreated this little ...   Jan 20 2003, 08:42
- - KikeG   I have only one computer too, but two soundcards i...   Jan 20 2003, 13:00
- - KikeG   So, all software that uses waveout (WinABX, abc/hr...   Jan 20 2003, 13:03
- - KikeG   thomaspf, make sure that in the settings of the pa...   Jan 20 2003, 14:50
- - thomaspf   Looks like we are getting on the same page here...   Jan 20 2003, 18:32
- - KikeG   In my Winamp 2 directsound plugin, I have no optio...   Jan 21 2003, 10:15
- - thomaspf   My DAC/surround sound proc is on it's way back...   Jan 21 2003, 21:58
- - KikeG   Ok, I've managed to get decent drivers for my ...   Jan 24 2003, 17:14
- - Continuum   QUOTE (KikeG @ Jan 24 2003 - 05:14 PM)Ok, I...   Jan 24 2003, 17:41
- - thomaspf   @kikeG I am expecting to get my DAC back this we...   Jan 25 2003, 00:31
- - KikeG   QUOTE (Continuum @ Jan 24 2003 - 05:41 PM)I h...   Jan 26 2003, 14:38
- - KikeG   Player: Winamp 2.81 Drivers: latest M-Audio Dio24...   Jan 26 2003, 14:41
- - thomaspf   I finally got my DAC back and repeated my tests vi...   Jan 29 2003, 08:46
- - Continuum   Are you sure that all volume levels are set to max...   Jan 29 2003, 11:53
- - KikeG   Yes, that could happen, but depends also on the se...   Jan 29 2003, 14:38
- - thomaspf   I set everything up as it shoud and also consulted...   Jan 29 2003, 19:07
- - thomaspf   Here is another tidbit. I had a conversation with ...   Feb 3 2003, 00:09
- - KikeG   This is strange, I hope I had a DTS decoder to mak...   Feb 3 2003, 09:25
- - Pio2001   I get bit perfect digital playback-record in loopb...   Feb 9 2003, 07:26
- - KikeG   I think the relevant results here would be for 44....   Feb 9 2003, 20:16
- - thomaspf   I just checked the Marian WEB site. It looks like ...   Feb 9 2003, 21:10
- - KikeG   OK, I've performed several RMAA (RightMark Aud...   Mar 6 2003, 16:35
- - KikeG   Well, a couple of months ago I managed to get mi C...   Jun 30 2003, 13:03
- - KikeG   Well, I just did a few more tests. I own now both ...   Aug 1 2003, 17:55
- - balazer   I understand that you need to use something like A...   Aug 19 2003, 10:02
- - KikeG   I already answered at the AVS thread. I did all my...   Aug 19 2003, 18:29
- - Patsoe   QUOTE (KikeG @ Jun 30 2003, 01:03 PM)There...   Aug 22 2003, 00:13
- - Peter   I suppose they just perform mixing/resampling at h...   Aug 22 2003, 01:10
- - AstralStorm   It depends on the card and its drivers. TerraTec A...   Aug 22 2003, 01:15
- - Patsoe   QUOTE (zZzZzZz @ Aug 22 2003, 01:10 AM)(ABX a...   Aug 22 2003, 01:22
- - Peter   No sane engineer seriously takes the possibility o...   Aug 22 2003, 01:37
- - AstralStorm   The test was brain-damaged. Mangled sample and no...   Aug 22 2003, 02:21
- - Patsoe   QUOTE (AstralStorm @ Aug 22 2003, 02:21 AM)Th...   Aug 22 2003, 08:06
- - KikeG   External hardware decoding of 44.1 KHz PCM-encoded...   Aug 23 2003, 18:30
- - KikeG   And, even when hardware directsound acceleration c...   Aug 23 2003, 18:35
- - Peter   That's because kernel mixer was designed to pl...   Aug 23 2003, 18:52
- - KikeG   Yes. But if I play something, I'd better prefe...   Aug 24 2003, 20:58
- - Patsoe   QUOTE (KikeG @ Aug 23 2003, 06:35 PM)So, in p...   Aug 24 2003, 21:52
- - KikeG   QUOTE (Patsoe @ Aug 24 2003, 09:52 PM)Well, i...   Aug 25 2003, 20:16


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