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  #21  
Old 12-21-1999, 08:00 PM
Jules Jules is offline
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Default Re: Pro Tools Sound Quality (continued)???

Thank you for your assurance,

Jules
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  #22  
Old 12-22-1999, 11:42 AM
TMS TMS is offline
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Default Re: Pro Tools Sound Quality (continued)???

I agree with blairl in regards to adhering to "blindfold" aspect of the test.This is VERY important. To not do so is like going to an audiologist for a hearing test and feeding yourself the tones. How many of us would think they heard 20K at minus 180db?

Craig
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  #23  
Old 12-23-1999, 12:20 AM
Jonny Atack Jonny Atack is offline
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Default Re: Pro Tools Sound Quality (continued)???

Well, I believe I was the first to post on the DUG regarding this mixer (despite emailed warnings from DUG friends to be careful not to look foolish) and that was because I was quite excited to hear the difference for myself.

I did believe I was hearing a difference in a single-blind test. Although I was told when the mixers were being switched, I didn't know which mixer I was hearing at each moment.

I agree with Blair1 that mixer A 'sounds' more harsh (particularly in the esses), but I felt that I was hearing more space and detail with what turned out to be mixer A, at least more than half of the time.

What bothers me, though, is that afterwards we reversed phase polarity in mono and the two mixers cancelled out completely within the listening limits of the AD8000, DDA desk, and Genelec monitors.

The question is: does that mean there is no difference between the mixers within the hearable limits of my system? Or could I still be hearing a difference in subjective detail even if all is cancelling out?

Thanks in advance to anyone who has an expert answer to this. Regards to all.
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  #24  
Old 12-25-1999, 02:07 PM
Dave Lebolt Dave Lebolt is offline
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Default Re: Pro Tools Sound Quality (continued)???

Hi Jonny,

It's not surprising that you're not hearing anything in the case you describe, but that's because the difference signal (in this case, the dither) is so far down in volume that you can't hear it above the noise floor produced by the rest of your gear. (No aspersions on your gear, it's just that the dither noise is way down… below -120 dBfs. As I stated in some earlier posts, there is no person I know that hears things down that low.)

In terms of what you hear during your listening tests, that's an open book… you may (or may not) be hearing differences between mixers that are caused by the side effects of the truncation or the dither. I'm just talking about the dither noise floor itself.

You can "see" the dither noise by command-clicking on the numeric indicators above the faders. This gives you a pretty accurate headroom indicator (although it looks to me like it may not be totally accurate below -120… I'll be checking into this). In any event, you'll see that if you sum together two signals from your shipping 24-bit optimized mixer, you'll get an infinity sign when you've flopped polarity (phase) on one or your bounce results. This indicates "no signal" at all. If you sum together the two different signals (Mixer A and Mixer B) and flop the phase on one, you'll see a reading on the HR indicator, which is caused by the dither noise from the dithered mixer. Hope this clears it up for you.

BTW, thanks for mentioning a bit about how you did your testing. You might want to try the test again with someone else switching in a setup where you are *not* aware of whether a switch has taken place… Instead, you ID changes by calling out the points where it sounds "better" or "different," etc. This is really flying "blind." I know that I, (and many others), have been caught off guard thinking that something had changed when looping over a section of music only to find that it hadn't been switched at all. It really helps sort out whether we are really hearing things or imagining that things have changed.
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  #25  
Old 12-26-1999, 04:32 AM
Jonny Atack Jonny Atack is offline
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Default Re: Pro Tools Sound Quality (continued)???

Hi Dave,

Thank you for your reply and your steady involvement on this issue.

Your point about double blind testing is valid, as psychology does play a role when we're all eager to hear a difference between the two mixers in the hope of an improvement.

However, what frankly surprises me is that the truncation difference between the two mixers doesn't show up audibly when phase-swapping. I would have expected to hear some remaining audio from truncation differences. Would you please shed some light on this for us?

Finally, I look forward to reading some other test result posts from the DUG community.

Happy Holidays to all.


[This message has been edited by Jonny Atack (edited 12-26-99).]
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  #26  
Old 12-26-1999, 03:34 PM
Dave Lebolt Dave Lebolt is offline
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Default Re: Pro Tools Sound Quality (continued)???

Hi Jonny,

The reason you wouldn't be likely to hear the results of truncation is that any audio artifacts generated are down below -100 dB, to my knowledge. Once again, that's just a bit too low down there for us to hear. Some folks believe that these components, (when added to audio we are clearly hearing at "normal" levels), produce audible artifacts that affect what we're hearing overall. That's part of what we're all trying to determine…

BTW, the test I was suggesting isn't what's called "double blind." It's just "blind." Double blind testing is when the operator doesn't know what they're switching *and* the listener doesn't know when it's being switched and what they're listening to.
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  #27  
Old 12-28-1999, 11:00 PM
hrob hrob is offline
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Default Re: Pro Tools Sound Quality (continued)???

I just found out it works the older farms; so, I haven't tried it, yet (soon, I hope).

I do have one suggestion. I've been playing with the non-dithering mixer and looking at the FFT of the result in SpectraFoo. From what I am seeing, you are more likely to hear the artifacts if you make a simple gain change on a stereo signal than with a multi-track mix.

I found that with more tracks involved, things actually tended to self dither somehow and the noise spikes I saw in the FFT with a single gain change disappeared. There is no theoretical basis for this; so, it's not something you can count on, but it does say that from a practical standpoint, you are more likely hear this with a single two track source than with a mix.

If you have access to the material, I would try this on a two track mix that was recorded with a stereo mic setup and very very good converters as this kind of recording tends to reveal things more than anything else.
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  #28  
Old 12-29-1999, 09:47 AM
digitaltvguy digitaltvguy is offline
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Default Re: Pro Tools Sound Quality (continued)???

MIXER A SEEMS VERY CLOSE TO 24 BIT MIXER.
MIXER B HAS A DISTINCT DIFFERENCE IN THE LOW END (SHOULD THIS BE OCCURRING?).

THIS WAS A BLINDFOLDED TEST.
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  #29  
Old 12-29-1999, 09:48 AM
digitaltvguy digitaltvguy is offline
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Default Re: Pro Tools Sound Quality (continued)???

Sorry I yelled.
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  #30  
Old 12-29-1999, 11:24 PM
Emanuel Emanuel is offline
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Default Re: Pro Tools Sound Quality (continued)???

I have been using Cubase for many years amd lately I've been thinking about buying a PT rig. This discussion makes me appreciate my Cubase even more. It uses 32bit processing throughout, including the VST plugins. Maybe Cubase with some Apogee converters will sound better than mixes done on PT? Has anyone compared this?
Of course Pt is the superior system in many ways I'm solely talking about sound quality and mixing algorithms here.

peace

Emanuel
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