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Author Topic: Why different results when mixing down ITB with different interfaces, buffer settings etc  (Read 7997 times)

A Deian

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Hi this has been bugging me for years. I've been mixing down my sessions using different buffer settings on the DAW and each setting makes the resulting track sound different.  A low buffer setting on one soundcard makes everything sound more forward but unnatural, whereas a high setting is more laid back but blurry.  Then in order to check if it's just my soundcard I tried to mixdown the identical session using four other soundcards at different settings.  The result is every soundcard yielded different sounding mixdowns even though the mix was all digital.  For example an EMU 1616m with Protools HD converters and was the least wobbly but also the narrowest and harshest.  Using the laptop's soundcard the sound was less wobbly with strong lower mids, but it's less 3D and the highs are rolled off.

Also I often "mixdown" mono files for each track within a session to save CPU and make things neater like a tape machine.  And it often sounds better too for some reason.  I've found that different buffer settings and also different soundcards affects the resultant file tremendously.  I've played back the tracks using different soundcards and you can always hear the characteristic of each soundcard.

Are these issues caused by jitter?  I was always under the impression that clocking or jitter only matters when conversion is occuring, but maybe I'm wrong.

Any wisdom would be greatly appreciated.  Digital is supposed to be more convenient but now it seems more straightforward to me when I was tracking and mixing on tape.

Andy
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Waltz Mastering

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Have you tried identifying the mixes that you bounced at different buffer settings and using different sound cards in blind listening and/or null test?

Patrik T

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I'd advice you to run test tones with different buffer settings on different cards and measure the output voltage on the DAC in use.

This is about the only way to actually confirm that:

- there is a problem. If so, voltage would alter with altered buffer. Does it?

- the different DAC's might output different voltages for the same digital ref. level. If so, audible confusion might arise.


Good Luck
Patrik
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Greg Reierson

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Have you done null tests?

There is NO jitter ITB.


GR
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A Deian

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Yes we've done blind tests with different people in two separate studios.  Also did a blind test at Metropois Studios in London with a mastering engineer called Tim Young.  We played him three digital mixdowns using three different soundcards and he heard the difference too.  He actually preferred the mixdown with the cheaper Tascam FW1804 soundcard, it was more grainy and less sterile (but wobbly).

At our studio we did one test just mixing down files with different buffer settings on the same soundcard (and repeat with alternate soundcard).  Then another test using 5 different soundcards on two separate computers.  We mixdown the same session on the same laptop with different soundcards engaged.  Then we listen back to the different mixdowns from the different soundcards on the same soundcard.  

The most disturbing is when we mixdown a mono track to a mono file.  The results are different with every soundcard.  Some lose bass, some add harshness (digidesign!), some lose depth (the laptop's own soundcard), some add bass (Native Instruments).  One thing we did find is all the firewire interfaces sound a bit blurrier than the USB, PCI, Cardbus cards.  Could be a coincidence, but maybe the firewire card can affect the sound?  Also noticed that the soundcards with Cirrus Logic branded converters tend to be less harsh than AKM, but again could be a coincidence.  The converters shouldn't matter anyway as we're mixing in the box?
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A Deian

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Haven't done null tests at home, but have brought it to three different mastering houses in London and they can all hear the difference.  Apart from Metropolis we also went to Alchemy Mastering.  There they could immediately tell that one mix sounded narrower than another.  Then we told them they were identical mixes using different soundcards and they were a bit miffed...
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TotalSonic

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The vast majority of DAW apps these days involve the soundcard only in playback and recording - and don't have any processing done with the soundcard or any effect by it at all when they are bouncing to disc.

I've had this confirmed to me directly to me for the DAW app I use (SAWStudio) by the author of the app himself - and it can be easily further confirmed with null tests.

You need to do some null tests.  If different bounces turn out to be data identical then I'd say the reasons you are hearing differences are most likely due to effects detailed at http://www.ethanwiner.com/believe.html - and yes, mastering engineers are effected by this just as much (and sometimes more, as they tend to be very attuned to minor differences) as others.

Best regards,
Steve Berson  

TotalSonic

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Greg Reierson wrote on Tue, 08 December 2009 10:24

Have you done null tests?

There is NO jitter ITB.



But there can be jitter at the DAC, even if playback is coming directly from a DAW.

Best regards,
Steve Berson

A Deian

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That's what the mastering engineer at Alchemy said.  But we did the same mixes again right there and then (so no one can accuse us of changing the mix), one with the laptop's sondcard and another with a high quality cardbus soundcard, and the two mixdowns sounded different.  I've never done a null test and am not sure how to go about it, but we can all hear on different systems that these soundcards are making a difference to the resultant mix.  The ME at Alchemy gave us all this theory about how this shouldn't be the case, but all of us including himself could hear that one mix was narrower and harsher than the other one.  Even my girlfriend could hear the difference when played the mixes on different monitoring systems and different soundcards.  I suspect it could be something to do with firewire or usb as we do all our mixes on laptops?
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TotalSonic

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A Deian wrote on Tue, 08 December 2009 11:07

That's what the mastering engineer at Alchemy said.  But we did the same mixes again right there and then (so no one can accuse us of changing the mix), one with the laptop's sondcard and another with a high quality cardbus soundcard, and the two mixdowns sounded different.  I've never done a null test and am not sure how to go about it, but we can all hear on different systems that these soundcards are making a difference to the resultant mix.  The ME at Alchemy gave us all this theory about how this shouldn't be the case, but all of us including himself could hear that one mix was narrower and harsher than the other one.  Even my girlfriend could hear the difference when played the mixes on different monitoring systems and different soundcards.  I suspect it could be something to do with firewire or usb as we do all our mixes on laptops?


To do a null test:
bounce to disc the same mix starting and ending at the same exact place (with in this case the single variable of what sound card or device or buffer setting you are testing).

Line the two versions up in separate tracks of a DAW, starting and ending at the same exact times.
Reverse the polarity (aka "flip the phase") of one of the 2nd channel.  
Bounce to disc once again.
If the two files are data identical the resulting file should have no audio on it whatsoever.  If not - the resulting file will show the differences.  

IF they are data identical then there are 3 reasons that are most likely why you might be hearing a difference:
* a jittery playback (generally cured by using a better DAC)
* different frequency response at the sitting position you are currently at versus the one where you were listening previously due to comb filtering in the room
* placebo effect

Best regards,
Steve Berson  

Geoff Emerick de Fake

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A Deian wrote on Tue, 08 December 2009 09:31

Yes we've done blind tests with different people in two separate studios.  Also did a blind test at Metropois Studios in London with a mastering engineer called Tim Young.  We played him three digital mixdowns using three different soundcards and he heard the difference too.  He actually preferred the mixdown with the cheaper Tascam FW1804 soundcard, it was more grainy and less sterile (but wobbly).

Regarding the influence of buffer size, I don't know your DAW, but I use Samplitude and it's a fact that changing the buffer size changes the behaviour of plug-ins,EQ's, dynamics (in particular those with look-ahead capability) and reverbs.
In Samplitude the project buffer size can be adjusted independantly of the soundcard buffer size; maybe in your app, you don't have the choice...?
Are you sure you're mixing 100% ITB. Seems to me this could happen if you looped the soundcard's outputs and inputs for printing your mix.
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Andrew Hamilton

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I thought I heard a difference with two different buffer settings in PTLE during a bounce to disk.  However, a null test proved that both mixes were bit-identical.  They still "sounded" different - as long as I knew which mix was which.  But I already knew that they couldn't be (different sounding), since x=x.  );  


Andrew

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subvertbeats

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Andrew Hamilton wrote on Tue, 08 December 2009 21:06

I thought I heard a difference with two different buffer settings in PTLE during a bounce to disk.  However, a null test proved that both mixes were bit-identical.  They still "sounded" different - as long as I knew which mix was which.  But I already knew that they couldn't be (different sounding), since x=x.  );  


Andrew




Out of curiosity I did the same with Cubendo a couple of years back, and had the same results.
All ITB of course.
With the proviso that I dont have any of these files to test and listen to, I think Steve is on the money in this thread.

A Deian

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Thanks for the helpful feedback I'll try the null test tomorrow.
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A Deian

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Oh and yes everything was mixed ITB.  The idea that buffer settings can change the way Samplitude reacts to plugins is interesting.  Did a lower buffer make mixes sound more "forward"?

Did a null test tonight after all.  I lined up two mixdowns of identical mixes (they were mixed to 256kpbs mp3s using the same laptop and program) and clicked on the phase switch for one of them.  One mix used a usb interface, the other used a firewire interface.

Bounced 17 seconds of audio and uploaded the result here:

http://www.sendspace.com/file/upyk62

I sincerely wish it did, but it doesn't sound like it nulled...


Ps: Just in case I also bounced two mixdowns that used the same soundcard with the same settings, and this time it nulled.

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