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  #1  
Old 04-14-2007, 06:30 AM
Matt_G Matt_G is offline
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Default Stereo Dithered Mixer

I've been reading the Digidesign 48bit mixer white paper & haven't been able to find an answer to this question, so I thought I'd ask it here in the hopes of getting some straight answers.

I've been thinking alot about the 'stereo dithered mixer' plug-in for Pro Tools HD & after doing some research I can't seem to find out at what point the 24bit dither is applied to the master output?

It can't be post fader because the fader is pre-insert on the master which would defeat the dither if plugins were inserted. So an educated guess would be that it must be applied after the last plug-in insert right? If this is the case it seems redundant in many ways. For example if you had an L2 or Ozone with 24bit TPDF dither on it why would you need Digi's dither? More to the point the plug-in bus truncates to 24bits on the I/O of each plugin inserted so you are already adding 24bit truncation distortion between plug-ins before the output is dithered to 24bits so how is Digidesign's 'dithered mixer' going to be of any sonic benefit at all if plug-ins or hardware inserts are used?

I have been running the dithered mixer in Pro Tools for years, but then after a recent thread on Glenn Meadows mastering webboard regarding 24bit dither, I got to thinking about how this works in Pro Tools HD & wondered where the dither is actually applied using the dithered mixer plugin. Anywhere it's put I can see potential for problems. Or am I missing something?

I think it's time Digidesign upgraded the precision of the plug-in bus, if the mix bus can run at 48bit why can't this be maintained right through the plug-in bus as well? I understand that it would use more DSP but sonic precision does come at a cost. At least we should have the option to turn this on just like the stereo dithered mixer plug-in. I think some of the native DAW's are heading in the right direction with high definition 64bit floating point precision maintained all the way through & they do sound incredible. soundBlade, Samplitude, Sonar & Sequoia all come to mind here.

Matt
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  #2  
Old 04-14-2007, 11:04 AM
el Daniel el Daniel is offline
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Default Re: Stereo Dithered Mixer

I would say it is added post master fader and pre first insert. 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. If it was post inserts there would be a 48 to 24 bits non-dithered truncation in the first insert of the master fader, and dither would be redundant since the last plug-in it is dithering its output to 24 bits and the wordlenght is the same between the last output insert and master output since there is no level change involved there.
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  #3  
Old 04-14-2007, 06:32 PM
frenchman frenchman is offline
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Default Re: Stereo Dithered Mixer

I have been working with pro tools for recording mixing and mastering for 7 years after quite some time having used "classic" studio gear.

Sure, 888/24 + MIX, had problems getting clean mixes in the box
Then for me came the "beta" dithered mixer, AD8000 and sony oxford eq : HUGE improvement. *Really* deep sonic perspective, stuff that was meant to sit "behind" in the mix actually sounded behind, with the right perspective.
Now HD with I/O96 and still my trusted ad8000 (still using oxford eq type 3 a lot), 24 bit 48k, and even *more* depth and perpective, sweet sound

Is there room for technical improvement in pro tools ? Of course there is, but speaking of dither hiss (audible on sessions with many tracks and plugs) I found it to be actually a *plus*. I believe that this is actually adding "air" to the recording. Call me crazy but I trust my ears on this
Quote:
"Anywhere it's put I can see potential for problems"
We could say this about analog tape machines, that is why everyone is trying to simulate them...

I firmly believe that criticism about Pro Tools has been beneficial, because Digi worked so that it sounds better than ever before (once you eliminate the plugs that actually have vastly inferior audio qualities than the host system)

I think that problem now lies elsewhere: I am not sure we have gotten the most of this system. This have moved so fast lately that I believe that we are many still on the learning curve

Speaking for myself I find my recent stuff to sound better than two years ago when I got the HD system, and that gives me motivation to further the search for better sound.

The white paper on the mixer has at least reassured me as to the technical quality of the system. So IMHO, at this stage I think that If you scale your levels properly, avoid overloading plugins, choose your plugins ruthlessly, (that is trusting your ears better than the nice GUI) and work on your monitoring acoustics, it might make these questions of where the dithering is taking place a little further down on the priority list...

an entirely subjective viewpoint of course !
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  #4  
Old 04-15-2007, 02:49 AM
Matt_G Matt_G is offline
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Default Re: Stereo Dithered Mixer

Quote:
I would say it is added post master fader and pre first insert. 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. If it was post inserts there would be a 48 to 24 bits non-dithered truncation in the first insert of the master fader, and dither would be redundant since the last plug-in it is dithering its output to 24 bits and the wordlenght is the same between the last output insert and master output since there is no level change involved there.
I guess this scenario makes sense, but then that dither would come undone after the first plug-in is inserted on the master & would need to be re-done after each plug-in. Meaning all the hardwork to dither your 48bit signal to 24bits is useless if it truncates through the proceeding plug-ins. It still doesn't prevent the audio truncating to 24bits on individual channel plug-in inserts either. The fact that this is left up to the individual plug-in manufacturers is a problem. Basically the more plug-ins you have in your session the more truncation distortion is being added to your audio. For one or 2 plug-ins this is less of a problem but for bigger sessions this weak link will become much more audible. It can also be debated that even if every plug-in did dithered back to 24bits before output that the accumulative dither would be additive & become unacceptable at some point.

Really the best way to implement precision in a DAW is to run it at the highest resolution through the entire path. In the case of TDM this would be 48bit (with 56bit accumulator) all the way through & dither the final output to 24bits on the way out. While the HD mixer has come a long way from previous versions, it is still a far cry from perfect & if you could compare what a 64bit floating point DAW sounds like to HD you would understand why I am mentioning this.

Anyway food for thought...

Matt
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  #5  
Old 04-15-2007, 07:35 AM
frenchman frenchman is offline
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Default Re: Stereo Dithered Mixer

Quote:
....While the HD mixer has come a long way from previous versions, it is still a far cry from perfect & if you could compare what a 64bit floating point DAW sounds like to HD you would understand why I am mentioning this.

Anyway food for thought...
Absolutly right, but we are strung between two opposite views, the quest for technical perfection on one side, and the quest for audio musicality on the other

I have come to listen to both sides : sometimes they agree, sometimes, they are right alternatively. So taking sides is difficult.

When (I actually witnessed this) in the eighties, manufacturers where telling us that never ever would anything beyond 16 bit be necessary, I actually believed them (!). Then came the hi fi crowd saying how bad it all sounded. Sure they seeemd a litlle wacky at first until manhy realised they where partially right.
Again when some people in 2000/2001 started questionning the pro tools mix bus, I was tempted to brush those comments away until the dithered mix plugin proved that they where right

But today I believe that the quality gap between a properly used HD system with dithered mixer, and the consumer is today the *main* problem.

I think that we are doing stuff with today level of quality that won't be ridiculous in twenty years time, unlike some stuff recorded and mixed in the eighties

Technical perfection is not really useful unless some real audible progress is made.
I think that for many of us, the present level of the hd dithered mixer is ok... until prooved wrong ;-)
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  #6  
Old 04-15-2007, 11:02 PM
Matt_G Matt_G is offline
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Default Re: Stereo Dithered Mixer

Quote:

Absolutly right, but we are strung between two opposite views, the quest for technical perfection on one side, and the quest for audio musicality on the other.
I don't believe this is true, firstly I'm not saying there shouldn't be a stereo dithered mixer unless it's not implemented properly. I'm a firm believer in the theory of the dithered mixer, in that any wordlength reduction should be dithered to prevent quantization distortion. The dither used in the 'stereo dithered mixer' is the TPDF variety & is not meant to add any colour to the sound. Because you hear the dithered mixer as adding 'air' or a 'musical' character, is probably more to do it preventing quantization distortion, which keeps your audio cleaner & truer to the original source. Quantization distortion on the other hand does not sound musical or add anything beneficial to the source material, in fact if it happens often enough it makes your audio sound veiled, flat & 2 dimensional. This is what I am arguing about with regards to the plug-in bus only operating at 24bits wide, it allows plugins to introduce quantization distortion which can quickly build up, I also believe that this can affect the results of the stereo dithered mixer.

There is many ways to colour sound in a musical way, plug-ins or outboard. Generally speaking, the most musical distortion & colour comes from valves, transformers or tape (the real stuff sounds far better then any of the digital emulations). I don't believe the DAW should contribute to 'the sound' of a project perse. The whole point of digital is to capture the analog source as true to the source as possible without taking the quality of the signal downhill. This starts with the quality of your converters, the precision & sample rate used to capture the source signal & how the DAW handles the audio from start to finish.

Quote:
I have come to listen to both sides : sometimes they agree, sometimes, they are right alternatively. So taking sides is difficult.
The same can be said about analog vs digital. There is no clear winner, you use whatever sounds best for the project you are working on. Sometimes it's best to leave a project all digital other times all analog & a lot of the time a combination of digital & analog works best. But again when it comes to digital I don't want it messing with the sound I've worked so hard to create in the analog realm. I like to have control of what colour I add, I want my DAW to be clean & bit transparent to preserve the sonic fidelity of the audio through the entire path. If I want an airy top I'll add as much as I need using my Sontec 432. If I want 3rd order harmonics I might use the Cranesong HEDD or an ATR half inch. Do you see my point? If you record a heavily distorted guitar through an Orange AC30 amp do you want the DAW to change the colour or character of that signal after it's been recorded if it sounds exactly how you want coming from the source? This signal isn't pure it's distorted in a musical way from the amp, so we just need Pro Tools to capture the sound from the source as accurately & transparently as possible without adding any colour of it's own. I hope this makes sense... Bit transparency doesn't equal cold & lifeless audio it means it sounds as close to the analog source as possible which should match the depth, width & tone of the source.

Quote:
Technical perfection is not really useful unless some real audible progress is made.
I think that for many of us, the present level of the hd dithered mixer is ok... until prooved wrong ;-)
If everyone had this mentality, we would never progress, thankfully there are some visionaries that strive for perfection. DSD is a good example of someone striving to achieve new heights in sonic fidelity. Of course if you are content to use your Pro Tools HD system for 20 years then that's great. Those of us who believe the finer details count will continue to strive for better sounding solutions. As a mastering engineer this is my job & probably why I am so finatical about the small things & why people trust me to handle their audio. I believe the small things do matter, it can mean the difference between a great record & a world class record.

Matt
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  #7  
Old 04-16-2007, 07:48 PM
el Daniel el Daniel is offline
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Default Re: Stereo Dithered Mixer

Quote:
Quote:
I would say it is added post master fader and pre first insert. 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. If it was post inserts there would be a 48 to 24 bits non-dithered truncation in the first insert of the master fader, and dither would be redundant since the last plug-in it is dithering its output to 24 bits and the wordlenght is the same between the last output insert and master output since there is no level change involved there.
I guess this scenario makes sense, but then that dither would come undone after the first plug-in is inserted on the master & would need to be re-done after each plug-in. Meaning all the hardwork to dither your 48bit signal to 24bits is useless if it truncates through the proceeding plug-ins. It still doesn't prevent the audio truncating to 24bits on individual channel plug-in inserts either. The fact that this is left up to the individual plug-in manufacturers is a problem. Basically the more plug-ins you have in your session the more truncation distortion is being added to your audio. For one or 2 plug-ins this is less of a problem but for bigger sessions this weak link will become much more audible. It can also be debated that even if every plug-in did dithered back to 24bits before output that the accumulative dither would be additive & become unacceptable at some point.

Really the best way to implement precision in a DAW is to run it at the highest resolution through the entire path. In the case of TDM this would be 48bit (with 56bit accumulator) all the way through & dither the final output to 24bits on the way out. While the HD mixer has come a long way from previous versions, it is still a far cry from perfect & if you could compare what a 64bit floating point DAW sounds like to HD you would understand why I am mentioning this.

Anyway food for thought...

Matt
The way audio is processed within plug-ins has to do with the plug-in architechture, some plug-ins dither their output and some plug-ins don't, I like to see TDM plug-ins like hardware inserts.
IMO additive dither from plug-ins is far from being a problem, 100 24 bits dither generations would be needed to increase the noise floor in 20 dB, and that would be 120 dB of dynamic range, no many converters can accomplish that and I don´t think it can be audible in the real world.

I agree with you respect running the highest resolution through the entire path would be better, specially for getting rid of all the points were signal can be clipped without being noticed if you are not careful with levels, such as aux tracks and some plug-ins that don't show when their inputs are clipping. Ironically it is not a problem at all in LE.

Cheers,
Daniel.
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  #8  
Old 04-17-2007, 06:41 PM
Matt_G Matt_G is offline
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Default Re: Stereo Dithered Mixer

Quote:

The way audio is processed within plug-ins has to do with the plug-in architechture, some plug-ins dither their output and some plug-ins don't, I like to see TDM plug-ins like hardware inserts.
IMO additive dither from plug-ins is far from being a problem, 100 24 bits dither generations would be needed to increase the noise floor in 20 dB, and that would be 120 dB of dynamic range, no many converters can accomplish that and I don´t think it can be audible in the real world.
Fair point, the use of compression & limiting can often bring up the noise floor quite dramatically though so that's another thing to bare in mind when talking about noise floor. The other thing is that it seems only a handful of plug-in manufacturers are dithering their double precision plugins to 24bits on output. So this is where the whole chain & stereo dithered mixer can come undone very quickly.

Quote:
I agree with you respect running the highest resolution through the entire path would be better, specially for getting rid of all the points were signal can be clipped without being noticed if you are not careful with levels, such as aux tracks and some plug-ins that don't show when their inputs are clipping. Ironically it is not a problem at all in LE.
Exactly, I've found the same thing with LE, which is pretty funny isn't it when you think that HD is supposed to be the professional platform at a premium price.

Matt
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  #9  
Old 04-18-2007, 07:00 PM
el Daniel el Daniel is offline
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Default Re: Stereo Dithered Mixer

Quote:
Fair point, the use of compression & limiting can often bring up the noise floor quite dramatically though so that's another thing to bare in mind when talking about noise floor.
Sure, but it should be taken into account that the best noise floor each track could have after tracking is the noise floor of your converters and, since that noise is much louder than dither noise, that would be the noise your compression and limiting will bring up.

100 24 bits dither generations per track would be needed to equal the noise of your great -120dBFS noise floor converters and therefore building up the noise floor by only 3dB. So given a session with 100 plug-ins in each track (I know there are only 5 inserts) your final noise floor would be only 3dB louder than in a session with no plug-ins at all, independently of the amount of compression and limiting you use.

Cheers,
Daniel
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  #10  
Old 04-19-2007, 08:27 PM
boogiemotel boogiemotel is offline
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Default Re: Stereo Dithered Mixer

I guess I have a simple question here

Do you guys reccomend the stereo dithered mixer for mixing in the box or do you leave the dithered mixer in the unused folder...unused
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