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[minister]

overlordofanalog wrote on Wed, 23 April 2008 16:57

Can some explain how I might achieve using the dithered mixer? No one has ever brought this to my attention before.

In your system HD/Library/Application Support/Digidesign/Plug-ins  (or Unused) you will find the stereo dithered mixer.

The HD mix engine is 48 bit fixed. Audio is passed from the plug-ins to the mixer. The way audio is processed within plug-ins has to do with the plug-in architecture : some plug-ins dither their output, others don't. Signal is always truncated to 24 bits in inserts and aux inputs in Pro Tools TDM, so the only way to keep the 48 bits resolution of the TDM mixer is to dither before the signal being truncated in the input insert or aux. The dither is added post master fader and pre first insert.

The accumulated dither in this architecture is nothing compared to even the noise floor of your convertors.

IMO, you should use it.

[Peter Beckmann]

Always use the dithered mixer, and have done since Digi first introduced it as an 'experimental option'

It sounds better: a lot better if you have a lot of tracks, busing and plugins going on. i.e. mixing.

At least now, the hit on your HD cards isn't too high.


Peter

[Etch-A-Sketch]

Berolzheimer wrote on Wed, 23 April 2008 12:14

It's a little cumbersome in PT actually- I find I have to record back into a track ( I know it's controversial but in the listening tests I've done the BTD function just didn't sound as good), either with a dither on on the master fader or then process the recorded mix with an AS dither, so then I have a 24 bit mix with 16 bits of information & 8 bits of zeroes, & then export that as a 16 bit interleaved file.

This is incorrect.  Dither does not add 0's.  Your mix on the new track is still a 24bit signal with 24 bits of resolution, not 16 with eight 0's on the bottom.  BUT!!! You added dither noise (which is a type of "hiss") to the signal.  That's the only difference at this point.  The mix has slightly more noise in it.  

When you convert to 16bit, the software simply discards the bottom 8 bits of the 24bit wordlength, which makes the exported file 16bit.  The dither noise you added in the previous step THEN helps smooth out the distortion that is caused by chopping off the bottom 8 bits.

Also, just for those who don't know, I should probably point out that there are different types of dither for different applications.  Certain types of dither you never want to "double up" or do more than once.  Those are usually the Noise Shaped dither.  Only put that in the audio as you are printing your master which will be directly converted to 16 bit.  

Dither without noise shaping is the type of dither that the digi mixer applies to the inserts and busses.  That type of dither is ok to add on top of itself.

[Etch-A-Sketch]

Bob Olhsson wrote on Wed, 23 April 2008 14:45

My understanding is that bouncing can change automation tracking because it's more accurate.

Actually Bob, the opposite is true.  The automation is LESS ACCURATE when doing a bounce to disk than when in playback/record.  I remember reading that in the Reference manual a long time ago and it was also reiterated in the official Protools classes I took a while ago.

I have also noticed that certain "variable" plugins like pitch correction, compression and reverb algorithms can vary A LOT more wildly from one pass to the next when using BTD instead of recording the mix back into a new track.

For whatever reason, bounce to disk is a different process for the mix engine and it isn't simply playing back the mix as though you hit play.  It is also why a lot of people had (and some still have) those "Bounce Handler Could Not Keep Up" error messages when bouncing to disk, but not when recording the mix onto a new stereo track.

[wwittman]

Someone should probably explain the whole process of choosing the dithered mixer

[Berolzheimer]

wwittman wrote on Wed, 23 April 2008 16:19

Someone should probably explain the whole process of choosing the dithered mixer

Good idea. The mixer in PT is a plug-in, in the plug-ins folder.  Look in there & you'll see 2 relevant items- "Surround Mixer.dpm" & "Stereo Mixer.dpm" .  Look in the unused plugins folder & you'll see "Surround Dithered Mixer.dpm"  & "Stereo Dithered Mixer.dpm".  Just swap places so the un-dithereds are in the unused plugs folder & the dithered mixers are in the active plugs folder.

[Berolzheimer]

Etch-A-Sketch wrote on Wed, 23 April 2008 15:51

Berolzheimer wrote on Wed, 23 April 2008 12:14 It's a little cumbersome in PT actually- I find I have to record back into a track ( I know it's controversial but in the listening tests I've done the BTD function just didn't sound as good), either with a dither on on the master fader or then process the recorded mix with an AS dither, so then I have a 24 bit mix with 16 bits of information & 8 bits of zeroes, & then export that as a 16 bit interleaved file. This is incorrect.  Dither does not add 0's.  Your mix on the new track is still a 24bit signal with 24 bits of resolution, not 16 with eight 0's on the bottom.  BUT!!! You added dither noise (which is a type of "hiss") to the signal.  That's the only difference at this point.  The mix has slightly more noise in it.   When you convert to 16bit, the software simply discards the bottom 8 bits of the 24bit wordlength, which makes the exported file 16bit.  The dither noise you added in the previous step THEN helps smooth out the distortion that is caused by chopping off the bottom 8 bits.

Derek if that's the case, why do dither plugs have 24,20, & 16 bit settings?  Is it just the level of the added noise?  If so I stand corrected.

[marcel]

Berolzheimer wrote on Wed, 23 April 2008 16:37

wwittman wrote on Wed, 23 April 2008 16:19 Someone should probably explain the whole process of choosing the dithered mixer Good idea. The mixer in PT is a plug-in, in the plug-ins folder.  Look in there & you'll see 2 relevant items- "Surround Mixer.dpm" & "Stereo Mixer.dpm" .  Look in the unused plugins folder & you'll see "Surround Dithered Mixer.dpm"  & "Stereo Dithered Mixer.dpm".  Just swap places so the un-dithereds are in the unused plugs folder & the dithered mixers are in the active plugs folder.

This only applies to HD (TDM) systems, though, right?

Not LE?

Best, Marcel

[eljaron]

Ok wow. First I've heard of this. I knew about dithering but had no clue there was a mixer option. Am I going to run into problems if I switch to the dithered mixer and pull up a session I mixed without the dithered mixer?

[Berolzheimer]

eljaron wrote on Wed, 23 April 2008 17:09

Ok wow. First I've heard of this. I knew about dithering but had no clue there was a mixer option. Am I going to run into problems if I switch to the dithered mixer and pull up a session I mixed without the dithered mixer?

The only problem is it will sound better and you might have to re-render for your ME .

If the session was absolutely maxed out DSP wise, there's a small chance it wil run out of DSP.

[grantis]

marcel wrote on Wed, 23 April 2008 18:46

Berolzheimer wrote on Wed, 23 April 2008 16:37 wwittman wrote on Wed, 23 April 2008 16:19 Someone should probably explain the whole process of choosing the dithered mixer Good idea. The mixer in PT is a plug-in, in the plug-ins folder.  Look in there & you'll see 2 relevant items- "Surround Mixer.dpm" & "Stereo Mixer.dpm" .  Look in the unused plugins folder & you'll see "Surround Dithered Mixer.dpm"  & "Stereo Dithered Mixer.dpm".  Just swap places so the un-dithereds are in the unused plugs folder & the dithered mixers are in the active plugs folder. This only applies to HD (TDM) systems, though, right? Not LE? Best, Marcel

Correct.

[Bob Olhsson]

minister wrote on Wed, 23 April 2008 17:21

The accumulated dither in this architecture is nothing compared to even the noise floor of your convertors.

It's also considerably lower than the accumulated distortion that you'll get as a result of not dithering.

[Berolzheimer]

Bob Olhsson wrote on Wed, 23 April 2008 20:07

minister wrote on Wed, 23 April 2008 17:21 The accumulated dither in this architecture is nothing compared to even the noise floor of your convertors. It's also considerably lower than the accumulated distortion that you'll get as a result of not dithering.

I'm very glad this subject came up, it's such a simple thing folks working in PT can do to improve sound quality yet so few know about it. I try to tell people about it whenever the issue of quality or the PT mix bus comes up...

I'm a dither missionary!

[wwittman]

Outside the box summing STILL sounds much better though

[Rail Jon Rogut]

The origin of the Dithered Mixer:

http://duc.digidesign.com/showflat.php?Cat=&Number=31366 &page=&view=&sb=5&o=&fpart=1&vc=1

Rail