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Author Topic: Please Explain (PT vs. Samp)  (Read 7409 times)

Ged Leitch

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Re: Please Explain (PT vs. Samp)
« Reply #60 on: August 24, 2005, 06:07:56 pm »

To Chris...
"pro tools reference guide" page 473 para 2.

Quote" pro tools TDM systems processes all audio internally at 24 bit"
pro tools reference guide - page 546.

quote" pro tools TDM systems support full 24bit audio input and output signal paths,with 48 bit internal mixing and processing!"

confusing?...
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Chris Cavell

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Re: Please Explain (PT vs. Samp)
« Reply #61 on: August 24, 2005, 06:28:52 pm »

It's been a really long time since I kept up with the innards of TDM, but it is my understanding that it works like this:

The summing buss is entirely 48 bit (or dual precision 24 bit).

All the insert points have fixed 24 bit single precision i/o streams (which made the master fader inserts function as expected, they're after the fader, and in TDM this means that the signal path after the master fader is 24 bit fixed).

Now here's where it gets confusing...and digi hasn't quite wrapped their heads around it themselves yet.

RTAS plugins need a 32 bit floating point I/O...so when they're placed on a track's insert, they change that insert point and all those that follow it on a given track to 32 bit float (AARGH!!!), and convert back to 24 bit fixed at the output of the last insert point.  This is why there are such huge restrictions regarding the placement of RTAS plugins in a TDM system...digi hasn't quite worked it out yet...but I'm sure they're doing their darndest to give the TDM guys just as much RTAS functionality as the LE guys.

When the audio comes out of the last insert point, it is passed as a fixed single precision 24 bit stream and placed in the middle of a dual precision 48 bit stream: the summing buss.  this leaves some empty bits above, and some below, leaving a pretty large amount of headroom as well as usually way more than enough lower bits to prevent quantization distortion within the mix buss itself.  The master fader then acts as a range selector across those 48 bits, choosing which range of 24 from within the 48 to send on to the master fader plugin section and/or on through to the converter.
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brett

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Re: Please Explain (PT vs. Samp)
« Reply #62 on: August 25, 2005, 09:21:05 am »

Chris , thanks for communicating that so clearly. I was trying to explain it but wasn't doing a very good job. Didn't know the terminology, and wasn't confident enough to tell people they were worng, but this exact topic has gone around before. When I first starting using PT I was dumbfounded why you couldn't use RSTAS on the bus or Aux sends. It was that conversion reason from native to TDM that they didn't work out in earlier versions. I use 6.1 with mix plus. From what I remember on the DUC RTAS was implimented in 6.9 for HD users. Correct me if I am wrong.

Any computer tech will tell you, your native processes are at the native processing buss's speed. So when you were saying LE was 24, I wasn't buying it. With the advent of G5's and 64 bit pc's, we will see new software supporting 64bit float. Native looks better and better. I am interested to see how next generation TDM systems will work. I am sure they have 64bit cores on the way when people start looking to native, they bring that stuff to the forefront. Right now people are still buying HD systems. When the matket demands higher processing, the market will get it. 48 bit obviously works. There are plenty of high end digital hardware devices that use 48bit fixed.

As for the sound variance that started this thread, I say it again, the bus algorythms and sound are unique to software just like they are unique to any other mixer, beit analog or digital. The sound may be diferent from one app or hardware mixer to the other.

I can tell you from using Cubase 32 and then using Cubase SX years ago, I notice a marked improvement in my audio quality. They both processed at 32bit float and both recorded 24bit audio. The change was in the switch to the Nuendo mix architechture and audio engine. So when you say LE doesn't sound as good as a Samp bounce, I say leave it be and use Samp!!!!!!
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Chris Cavell

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Re: Please Explain (PT vs. Samp)
« Reply #63 on: August 25, 2005, 09:30:52 am »

Quote:

From what I remember on the DUC it was implimented in 6.9 for HD users.


Digi has managed to slowly increase the RTAS functionality within their professional lines.  The "what can follow what" restrictions remain iirc, but you can now place rtas plugs on aux tracks (a big bold + for producers who use alot of softsynths and samplers).  I don't think you can put them on a master fader yet.
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Bob Olhsson

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Re: Please Explain (PT vs. Samp)
« Reply #64 on: August 25, 2005, 09:38:33 am »

FWIW the only native Waves plug-ins that dither to 24 bits or less are the L-1 and L-2. L-1 has been double precision since I think version 4 which was when 24 bit dither first became an option.

I've had a hunch for 5 years that TDM will be replaced by some kind of a native co-processor scheme that gets around the latency issues. TDM is amazingly long in the tooth and 56k assembler code is prohibitively expensive to write.

TotalSonic

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Re: Please Explain (PT vs. Samp)
« Reply #65 on: August 25, 2005, 09:42:10 am »

brett wrote on Thu, 25 August 2005 14:21


Any computer tech will tell you, your native processes are at the native processing buss's speed. So when you were saying LE was 24, I wasn't buying it. With the advent of G5's and 64 bit pc's, we will see new software supporting 64bit float.


Brett -
It's important to note that buss speed is not the same as teh bit depth of an internal processing calculation routine.  You can easily have 64bit floating point math calculations done with a 32bit OS.  Theoretically the calculations will get done faster with the 64bit OS.  

Best regards,
Steve Berson

TotalSonic

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Re: Please Explain (PT vs. Samp)
« Reply #66 on: August 25, 2005, 09:44:35 am »

Bob Olhsson wrote on Thu, 25 August 2005 14:38

FWIW the only native Waves plug-ins that dither to 24 bits or less are the L-1 and L-2. L-1 has been double precision since I think version 4 which was when 24 bit dither first became an option.


L3 also has these same dithering options.

Best regards,
Steve Berson

Bob Olhsson

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Re: Please Explain (PT vs. Samp)
« Reply #67 on: August 25, 2005, 09:47:55 am »

true!

A lot of floating point processors operate at more than 64 bits too.

masterhse

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Re: Please Explain (PT vs. Samp)
« Reply #68 on: August 27, 2005, 11:14:25 am »

Gerald Leitch wrote on Wed, 24 August 2005 16:19

Does'nt say whether it dithers output to 24 bit or truncates though?


I believe that that is the main difference between the PT dithered mixer and non-dithered mixer.

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Ronny

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Re: Please Explain (PT vs. Samp)
« Reply #69 on: August 27, 2005, 11:44:16 am »

masterhse wrote on Sat, 27 August 2005 11:14

Gerald Leitch wrote on Wed, 24 August 2005 16:19

Does'nt say whether it dithers output to 24 bit or truncates though?


I believe that that is the main difference between the PT dithered mixer and non-dithered mixer.




A word length reduction is a truncation, regardless of whether dither is applied or not. It's not either, I truncated or I dithered, being two opposing events, it's I truncated without dithering or I truncated with dither applied. A dithered word reduction is a truncation, because regardless of applying dither or not, you are still quantizing bit data.
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masterhse

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Re: Please Explain (PT vs. Samp)
« Reply #70 on: August 27, 2005, 12:47:00 pm »

Ronny wrote on Sat, 27 August 2005 11:44


A word length reduction is a truncation, regardless of whether dither is applied or not. It's not either, I truncated or I dithered, being two opposing events, it's I truncated without dithering or I truncated with dither applied. A dithered word reduction is a truncation, because regardless of applying dither or not, you are still quantizing bit data.



True Ronnie, I assumed that the original post was a shorthand way of asking does PT dither before truncation.
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Tom Volpicelli
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bassman

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Re: Please Explain (PT vs. Samp)
« Reply #71 on: September 05, 2005, 02:38:22 pm »

Shamless plug here but when I come across these type of threads, I find the people that might be interested in what I do.  I am writing a book all about plug-ins and the DAW technology called "Plug-in Power: the Complete DSP Reference Guide" coming out this fall/winter.

<  http://www.amazon.com/exec/obidos/tg/detail/-/1592009530/qid  =1125588731/sr=8-2/ref=sr_8_xs_ap_i1_xgl14/103-6411458-44262 18?v=glance&s=books&n=507846>

I happened upon this thread doing research on pan law among other things and will have much information on this and other topics that come to the surface of the boards all the time.  Hopefully my efforts will consolidate much of this information and will be helpful to one and all wishing to improve their DAW audio results.

To add to the topic at hand, an earlier post described the PT bit depth chain and was accurate for the TDM systems. The plugins are connected by 24-bit busses and the mix buss is a custom scaled 48-bit systems that is reduced to 24 bit for output to the master plugins and analog converters. This is as per Bobby Lombardi, who handles plug-in design for Digi. I am double-checking all my info for the book as I go along...

PT LE is a native app and runs internally at 32-floating point until final output which MUST be reduced to 24 bit fixed point in order to be converted to analog!  This is something that gets confused often.  32-bit floating point files cannot be directly played back via analog converters.  Something must quantize the file to 24-bit fixed point in order to work.

Both fixed point and floating point math involves some errors during typical mixing. These errors crop up at different times and with different effects. I'm sure those differences will be debated as long as possible out here on the boards. Both systems are capable of tremendous work and if understood, can be maximized for each systems potential while avoiding any weaknesses.

The question I would like to add is unless you are using dynamic or moving pans in your mix, do you think that the pan law will truly effect the outcome? I believe it won't. If a sound is panned in one spot, you will adjust your level accordingly regardless of the pan law setting.

Now, importing and exporting between DAW's that have differing pan laws will surely change the sound, but if the pan law does not change, how does that affect the mix for non-moving sound sources?

-ashley shepherd
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