Protools LE mixer

[protoolsman]

Hey guyz,

I never thought about this but what kind of mixer is PT8 LE using. See, my Mix+ and HD have a choice between stereo mixer, stereo dithered mixer and surround dithered mixer. For some reason Surround dithered mixer is most DSP friendly and sound the best (to me). But in LE you don't have a choice. So: is LE's mixer dithered?

[protoolsman]

Let's reply to myself (to keep it here)... How many of you have any clue on what's going on dither wise in PT8?

[earth tones]

Based on what I have read in the Pro Tools 8 Reference manual, I would guess that the mix buss is not dithered until you apply dither (via a plug-in) to the Master Fader track. Can't say I know this for sure though.

From pg. 960 of the PT8 Reference PDF:

"ProToolsLE and M-Powered systems use 24-
bit audio input and output signal paths, and
internal 32-bit floating point processing for
mixing and audio processing
Using Dither on an Output Mix
ProTools includes real-time dither plug-ins that
improve 16-, 18-, or 20-bit performance and reducing the
bit depth of an output mix."

pg. 867:

"Some AudioSuite plug-ins can
automatically apply dither when processing.
You can select this option in the Processing Pref-
erences page.Dithered Mixer Plug-ins (ProTools HD Only)
Digidesign has developed a mixer that provides
all of the benefits of the standard Stereo Mixer"

[protoolsman]

OK...That's clear. Thanks for that. Now, on the HD session it says dither "on every node". Which means (I think) every single input output.
Another question than: does mix made on LE sound better on HD because of dither? Or...and....if...I'm kind of stuck.

[dsw]

Sounds better on HD because of the AD/DA conversion and Automatic Delay Compensation.

You don't mention the interface you're using with your systems, but IMHO the conversion is the thing that makes the most difference between any DAW system.
Other variables such as room, pre's, technique, sun spots, etc.... come into play obviously but to quantify the difference between DAWs based on dithering is, I think, really hard to do.

[protoolsman]

I am using a 002, but I am trying to figure out the difference when mixing out of the box.Lowering the volume on a track will lower the quality. Dither would make the noise floor a little higher but have less distortion. Who knows the answer to this?

[earth tones]

I am not sure if I understand your question...and how you are relating the decrease of a track's level in a mix to dither.

Dither is a psychoacoustic technology (algorithm) that is used to salvage the sonic data within a bit-depth range which will eventually be truncated (wordlength reduction). The most common situation for the application of dither is when a 24-bit recording/mix is bounced or mixed down to a 16-bit format. What happens to bits 17-24 when this happens. Without dither, they are simply gone. So say goodbye to the audible data that was being stored in that range. By applying dither (complex noise) it allows the audible data within the planned-for-truncation 8 bits to be preserved within the range of the resulting 16 bits. (go read about dither for a detailed depiction of how dither magically toggles this data into the 16th bit).

By adding this noise to the signal, it would decrease the signal to noise ratio, but marginally. Plus, most of the modern dither algorithms have shifted the frequency content of the dither signal far above the upper limits of human hearing (20kz).

[protoolsman]

Agreed; so if I lower level on a track I will use less bits of the 24 available. Or: distortion gets higher (because of rounding of). So in HD or TDM sets you can choose a dithered mixer that will put dither on every single track. The noisefloor gets a little higher this way but distortion figures are better.

Maybe this link to duc.digidesign will clear things:
http://duc.digidesign.com/showthread.ph ... 901&page=3

I am in no way a computer wizz but I would really like to know what the fuzz is about on TDM, and if this also is a factor in LE.
But thanks for all the help already! [/img]

[locosoundman]

most of the modern dither algorithms have shifted the frequency content of the dither signal far above the upper limits of human hearing (20kz).

This is true for higher PCM sample rates and Sigma Delta, but I am not sure that this applies to lower sample rates, since I would think that the anti-aliasing filters would effectively remove the dither.

Noise shaping tends to place most of the energy in the higher frequencies since this is a range that many people cannot really "hear" except at high intensity, but this is based on perceptual models, and still falls within the audible spectrum.

I can only speak as to what I hear: when I am applying 16-bit dither to mixes at 44.1 and 48, I tend to prefer the sound of the flat dither as opposed to the noise-shaped (not always - but most of the time). The high frequencies seem to get "blurry" or "clouded" to my ear when I use the noise-shaped.

[wedge]

Lowering the volume on a track will lower the quality.

You mean, when tracking? Not necessarily... There's a lot more wiggle room than you might think, especially with 24 bit... Also, why don't you just wait until the CD burning/mastering point to have dither applied? Everything up until then can be whatever bit depth you wish to use...

[leigh]

Hey guyz [sic],

I never thought about this but what kind of mixer is PT8 LE using. See, my Mix+ and HD have a choice between stereo mixer, stereo dithered mixer and surround dithered mixer. For some reason Surround dithered mixer is most DSP friendly and sound the best (to me). But in LE you don't have a choice. So: is LE's mixer dithered?

NO

LE's mixer is not dithered, because LE keeps it 32-bit floating point. Hence, no need to dither.

Now, stop losing sleep over this kind of stuff and go make something beautiful.

[protoolsman]

To Leigh: LOL , I already was!
It's the kind of thing that get's stuck in your head. I did my reading on floating pioint calculations and came to the conslusion that because of the "floating" aspect there is less rounding of going on. I guess the question "why not use this in HD" is pointless?

I still enjoy protools 8 very much and can't wait for my 003 with Black Lion mod.
Still making beauty Leigh

[chris harris]

good gawd!!!

do you hear a decline in quality when lowering a fader?

If yes, then I say you're full of shit.
If no, then what difference does it make?

[protoolsman]

Don't worry, I am just wondering how this all works, not at all a*** about it. And to answer your question: Working in HD (now) YES I can hear the difference. I hear it on reverb, on guitar and piano. Not so much on drums. But I do know there are MANY variables and reasons why this is. I have not yet tried this in LE.