Dithering from 32 Float to 24 Bit
 

If I am working in 32 float and bouncing 24 bit files to disk, do I need to dither using a plug-in (IDR, PT Dither...etc.), or does PT dither on its own sufficiently?

Re: Dithering from 32 Float to 24 Bit
 

Anyone? Wondering if I'm missing a critical step.

Re: Dithering from 32 Float to 24 Bit
 

If I needed 24 bit for compatibility, I would just begin in 24 bit and not worry about dithering until I wanted to burn a CD in 16 bits.

Re: Dithering from 32 Float to 24 Bit
 

And if you were working in 32 and bouncing to 24?

Re: Dithering from 32 Float to 24 Bit
 

The first question, do any of your dither plugins even have a 24 bit setting?

If so, did you try it both ways and see if it sounds different?

Don't have PT10 so I really don't know... but if the dither plugins have a 24 bit setting, I'd use it.

Re: Dithering from 32 Float to 24 Bit
 

Wow! Great question! Checked and they don't. Was just assuming they must. Guess PT must do its own dithering on bounce that everyone is happy with?

Re: Dithering from 32 Float to 24 Bit
 

if PT10 is the same as PT9 then PT does NOT dither on bounce to disk. it does dither when one uses the export method (after one has recorded the mix to a stereo track...16bit only IIRC)

check this one out. it has 24bit dither...http://www.pspaudioware.com/plugins/...ors/psp_xenon/ hope that helps

Re: Dithering from 32 Float to 24 Bit
 

I just did my 24 bit dither demo for an acoustic jazz mix client yesterday. I didn't tell him what I'd changed and he was floored by how much worse it sounded when I bypassed the dither plug.

My current fav. is PSP audio's xenon limiter. You can turn the limiting off with the control at the center-bottom while leaving the dither on. I use 24 bit with no noise shaping. My tests found this to give the best final 16 bit results also using flat dither down to 16. I like it better than 32 bit float.

If the mix did not employ dither, noise-shaping can sound better going to 16 bits. Using the dithered mixer in a TDM system accomplishes the same thing as the PSP plug in a native system.

Re: Dithering from 32 Float to 24 Bit
 

I still have TDM cards, so I have the 24 bit mixer, and doubt I would see much benefit from a $249 dither plug-in unless I work outside of HD.

But it brings up an interesting point. If 32 bit is preferable for HDX and non-HD, and 24 bit file saves should be dithered, why are none of the Avid included dithers capable of 24 bit dithering?

Re: Dithering from 32 Float to 24 Bit
 

I've been asking them that for a decade!

Re: Dithering from 32 Float to 24 Bit
 

one other thing, and someone can correct me if i'm wrong as i have not worked in 32bit in PT10 yet, but if you RTD (record to disk) then export at 24bit, PT10 will automatically dither...no plug needed. but again, not so if you wanna use BTD.

Re: Dithering from 32 Float to 24 Bit
 

Yes, if you bounce a mix within Pro Tools and use "Export Clips As Files", it will automatically add dither for whatever down-sampling is occurring, including 32 bit floating point to 24 bit. (See Pg 346 of the Ref Guide).

Like mykhal said, Bounce To Disk does not automatically add dither so you'll need a dither plugin with a 24 bit setting if down-sampling from 32 bit floating point (see Pg 1082 of the Ref Guide).

Re: Dithering from 32 Float to 24 Bit
 

nice on bringin' some ref pages to the discussion!!;)

Re: Dithering from 32 Float to 24 Bit
 

Good to have the page numbers in your post, PD-John, thanks.

As a side note to dithering mixdowns and bounces, there is also an Audiosuite dither accessible in the "processing" tab of the HD preferences tab at the bottom of the "setup" pull-down.

The Audiosuite dither does support 24 bits, but is (per page 995 of the ref manual) automatically applied to the Audiosuite plug-ins for Gain, Normalize, Smack! and Sonic NoNOISE.

Just when you thought you had dither nailed...

In reading the reference manual, it sounds to me like bouncing from 32 bits to 24 bits without dither is ok, but I would have to do a comparison to know if I can hear a difference. Maybe it is cumulative, but I am still working in the HD 24 to 48 bit (processing) mixer that dithers down to 24 bits, so the original post is less of a concern to me than to those who want to record in 32 bit float.

Re: Dithering from 32 Float to 24 Bit
 

Just having a stab in the dark here, but in a theoretical sense won't the internal workings of a 32 bit float point session require much less dithering (if any) to 24 bit, because the virtually unlimited headroom will mean that any quantization distortion introduced when down-sampling will be pretty much inaudible? I'd expect it to be far less apparent than going from 24 bit to 16 bit without dither anyway.

It would be interesting to see in the Ref Guide how much dither is applied in dB FS for each down-sampling stage. Perhaps someone with a lot more knowledge than me could shed some light :-)

Good stuff here.. Glad to get clarification on this as I wondered about this myself.. I always RTD tho then export so this is good to know...


Sent from EPIC 4G using Tapatalk On'eim...

Re: Dithering from 32 Float to 24 Bit
 

The important thing to understand is that dither adds 3 dB. of noise per bit reduction while not dithering adds 6 dB. of distortion! 32 bit float is still 23 bits and is difficult to dither. 64 bit float or 32 bit fixed are when you can begin to ignore dither in my experience.

Re: Dithering from 32 Float to 24 Bit
 

Got the PSP Xenon and dithered from 32 bit float to 24 bit. Notice a bit more clarity on the dithered bounce!!! Thanks so much for the advice!!!!!! One last consideration, is it better to just work at 24 bit if I have to deliver at 24 bit? Is it better on the sound not to bit reduce at all, as panamajack suggests. Working a session at 32 bit float has the benefit of pretty much no concerns with clipping, but if I am sacrificing resolution in the end...might not be worth it. Thoughts?

Re: Dithering from 32 Float to 24 Bit
 

My tests in Samplitude showed better sound in the final product if I dithered to 24 rather than saved to 32 float. I notice not only more clarity but much better image depth and width. Once I began listening for that, flat dither became a real no-brainer.

It made a huge difference in our listening tests for the Kramer tape project. A depth effect I love about old Ampex recorders turned out to be the character of the tape hiss! That depth effect goes away when you turn off the dither.

I find the whole thing fascinating.

Re: Dithering from 32 Float to 24 Bit
 

Bob, you're rad, man. Appreciate the romance for sonix. Very damn cool.

Re: Dithering from 32 Float to 24 Bit
 

I found a short explanation of why Avid has moved to the 32 bit float - 64 bit float mix setup in their Knowledge Base.

Q: Why did Avid switch from 24-bit processing/48-bit fixed summing to hardware that offers 32-bit floating-point processing/64-bit floating-point summing, and what does it mean for me?

A: There are several reasons for the transition. A 64-bit floating-point mix bus provides more than 1,000 dB of headroom, which is more than enough to handle the huge track counts that Pro Tools|HDX can deliver. Also, by moving the insert paths to a 32-bit floating-point format, Pro Tools|HDX offers much more dynamic range for plug-in processing, making it nearly impossible to clip the plug-ins, while also being able to handle greater than 24-bit audio file formats.

Many of you have told us that even with dual-precision plug-ins processing at 48-bit, the path between inserts on Pro Tools|HD was still limited to 24-bit — thus, limiting any gains. With Pro Tools|HDX, all data streams are maintained at full 32-bit floating point and then summed in the DSP mixer at 64 bits. Our beta customers told us that they could hear and appreciate the difference.

My guess is they will soon be adding a white paper explaining this in more detail. There is a thorough explanation of the PT 48 bit mixer at:

http://akmedia.digidesign.com/suppor...ixer_26688.pdf

The above white paper explains what used to be top shelf before HDX hit the scene.

The newer black HD I/O interfaces also have superior dynamic range specs in their converters. The ADC is 122 dB, the DAC is 125 dB. The 192 interfaces had ADC of 120 and DAC of 118 dB (A-weighted). So, with a very high quality amp and monitoring setup, and in a well treated listening environment, the specs would indicate they are an improvement.

But the style of music comes into play as well. Not all musicians are performing on a $3 million Stradivarius.

Re: Dithering from 32 Float to 24 Bit
 

If neither your recordings or your mix are clipping anywhere, you don't need to do anything.

What most people seems to not understand about the 32 bit float on PT10, is that it's an invisible feature. Your metters still work the same way as if you were working at 24 bit. You can actually switch the session parameters from 24 bit to 32 bit float without actual changes to the files.

The reason for this is that 32 bit float is the same as 24 bit, except it has a lot more headroom. If you clip a recording in 24 bit for 3 dbs, the file gets clipped. If you clip by 3 dbs while using 32 bit float, the mixer metter shows your recording clipping, but the file supports that clipping with that extra headroom (meaning that you can lower the clip gain and have no distortion at all).

If you convert your 32 bit float session to 24 bit, you don't need any dither because the only thing getting truncated is the extra headroom. Any wave information on the file bellow that extra headroom is perfectly compatible with 24 bit and show the same levels in the mixer.

The keyword here is "float". It's not 32 bit vs 24 bit. It's 32 bit float vs 24 bit. 32 bit float "peaks" at the same exact point as a 24 bit file. The difference is that it has the space to store more bits over that peak point, while 24 bit simply hits the roof and distorts.

HTH

Francisco

Re: Dithering from 32 Float to 24 Bit
 

That makes sense if dithering does nothing for a BTD from 24 to 24. Is this the case? What then is this X-factor Bob notices? Maybe that difference is just in comparing bouncing from a 32 float session to 32 float files versus bouncing to 24 bit files dithered from the same 32 float session? If that is the explanation, than you're saying that from 32 float to 24 I need do nothing. Exactly what I was wondering. I don't know if this is a contentious area or not, but it seems that there is a lot of misunderstanding...perhaps just my own.

Just put a good 24 bit tpdf dither like the one from psp xenon across your 2buss and listen while you hit play...

No bounce. Listen.
Bypass. On. Bypass. On.

Make up your mind for yourself afterwards...

Re: Dithering from 32 Float to 24 Bit
 

yep...exactly...

Re: Dithering from 32 Float to 24 Bit
 

Better than that... don't trust your ears. Trust exact science.

1) Send your final mix to 2 busses, both receiving exactly the same, both sending to monitors.

2) Insert your dither plugin in the first one.

3) Insert some plugin like Channel Strip on the second one and invert the phase.

Now, you can play your mix and start switching the bypass control on your dither plugin. If something is really different, you will hear sound. If everything is exactly the same on both busses, you will hear nothing.

Note: In any case, for your dither plugin to be able to work, it should be able to receive audio at 32 bits so it can dither to 24. If it starts by receiving only 24 bits (a therefore clipping over that), making it dither to 24 bit would be just silly.

------------------
EDIT: Make sure you are working with ADC enabled for this test to work properly!
------------------

HTH

Francisco

Dear Mister lab coat...

Do you know that channel strip is a bit transparent piece of code to start with?

Unless you use a "legacy" TDM system (where connections between inserts ARE at 24 bits - native, PTN and HDX are at 32 between inserts) the comment about "truncation" (not clipping btw) is irrelevent.

Of course the noise from dithering is always gonna show up as difference (as is any distortion products from truncation somewhere in the chain btw) invalidating the test.

Bob O. might have said it in this very thread, TPDF dither (flat triangular) adds 3dB of noise to the signal per bit reduced. However the audio information is completely preserved.

Truncation adds 6dB of distortion products per bit truncated. All info under the truncation point is lost.
Also by nature their inharmonic components these new components are very unmusical and disruptive to the pgm material even at very low level.


While you pounder this I have an album to master an a remix to do.

Cheers!

Re: Dithering from 32 Float to 24 Bit
 

In Pro Tools 8 and 9, BTD with and without Dither resulted in files that would CANCEL each other out when one was inverted.
This proves that if you "forget" to add the dither plug-in on your Master Fader before bouncing, that it would dither anyways!

This made it very hard to teach students the chapter(s) on dithering, bouncing to disk, etc.

I have ALWAYS been a fan of Buss-To-Track mixes, and then Exporting the subsequent Region / Clip as a File to get the "automatic" / Default dither when moving from 24 bit to 16bit.

I can't see why they would now change back to altering the "behind the scenes" dithering on Bounces from 32 to 24.


Does anyone have any idea how this all works in Pro Tools 10 if one BUSSES to a New Audio Track, BUT first changes Pro Tools Bit Depth from 24 to 16 BEFORE recording the new track? Dither or no Dither automatically applied or needed??

THAT is a good question.
Also did you check your null test with a bit scope?
I'm not sure residual products (such as dither noise) at lsb level would be detectable by ear unless you have an incredible monitoring chain and control room... Not sure but wondering?

Cheers!

Re: Dithering from 32 Float to 24 Bit
 

While I'm not discounting Bob O's observation while listening, I'm going to stick my neck out here and make a statement that may rile a few. Dithering when going from 32 bit float to 24 bit fixed is little different than adding dither after a file has already been truncated. 32 bit float only stores a 23 bit significand (+1 implied) and an 8 bit exponent. In other words, the audio portion of the 32-bit float word only contains 24 bits. It is understood that floating point has a variable noise floor since having an exponent just means that the decimal point can shift up or down. For the same reason, trying to dither upon conversion to fixed point would result in a file with low-level detail (within the dither) modulated by the amplitude of the signal. So if there really is detail to preserve, it may happen ok when the signal is -18 dBfs peak, but not when the signal is -2 dBfs peak.

Frankly, it's not realistic to believe that dithering from 32-bit float to 24-bit fixed is going to gain anything in the area of quality. That's why Avid has never bothered to implement 24-bit dither.

Re: Dithering from 32 Float to 24 Bit
 

Actually I was testing going from mix files written to 32 float and then dithered to 16 vs. mix files dithered to 24 and then dithered to 16. I agree much of the damage has probably already been done by truncating to a 32 float file but I wouldn't assume 32 float and not higher precision is what is being dithered to 24.

Really the best test is to simply listen for yourself.

Re: Dithering from 32 Float to 24 Bit
 

Thanks a lot for this explaination! This is the only thing I've read on the subject that makes me fully understand it! You also answered all the questions I had about 32-bit float! :-)

Re: Dithering from 32 Float to 24 Bit
 

Has everyone forgotten that PT does it's processing and bussing at 32 float? Unless you have HDX or a Native card (in which case there's a mix of 32 and 64-float going on), every time you play back a 24-bit PT session, you're hearing a 32-float stream being converted to 24-bit fixed so it can be sent to your converters. That's exactly the same thing as playing back 32-float files. Whether the session format is 24-bit or 32-float, if you have any mixing, plug-ins, or even gain change going on anywhere in the session, the bit stream at the master bus is taking advantage of 32-float math, and that 32-float signal is being converted to 24-bit fixed so that you can hear it, because there's no such thing as a 32-float DAC.

I have found that a 24-bit fixed file converted from a 32-float file tends to sound better if 24-bit TPDF is added prior to conversion. I understand that the low level detail is then being modulated by signal amplitude. But somehow it seems to make it hold up better to further processing down the line.

:-$
Cha Ching!

Re: Dithering from 32 Float to 24 Bit
 

Right! To clarify, the null test produces no Residual MUSICAL leftovers.
The only thing left IS the dither noise. (sorry, didn't do a bit scope yet)
The original 24 bit file,
a POW-r Dithered 16 bit Bounce,
an UNDITHERED 16 bit bounce,
and an internally bussed then exported 16 bit file (which gets the default Digi Dither):
when ANY two files are played against each other and one is inverted, sonically identical very low level "Noise" is all that is left (@ full volume on the mains in the studio), even against the 24 bit original.

I did this with an average level 24bit acoustic ballad mix that had been processed with audiosuite for "mastering".

Since the files were INVERTED in the 24 bit session with audiosuite, the default audiosuite 24 bit dither is applied.
But there should be something more definitively different between the noise leftovers given the pages and pages of back and forth over the different Noise Shaping options within POW-r Dither alone.

Re: Dithering from 32 Float to 24 Bit
 

I believe there is some misinformation here about Bounce To Disk. I've been using BTD when bouncing down ideas and I always tell PT to bounce as a wav file then under it I switch it from 24 bit to 16bit and the file comes out as a 16 bit wav file.

Not only does it show as 16 bits when viewing it in various programs but it plays on my ipod and as some of you know older iPods will only play wav files that are 16 bits.

Re: Dithering from 32 Float to 24 Bit
 

just another question:

why (according to the manual) is dither applied when exporting from 32bit to 32bit?
it is also mentioned, that no dither is applied when exporting from 24bit to 24bit.

That sounds strange to me!

And: What dither (16, 18, 20bit) is used when exporting to 24 or 32bit?

Thanks,
Gandlz

Re: Dithering from 32 Float to 24 Bit
 

You are trying to make some valid points but being let down by multiple inaccuracies. Non-legacy TDM Pro Tools uses a 64-bit mixer, and plugins use a combination of 32-bit and 64-bit floating point processing. That's true of Pro Tools standard, HD Native, HDX etc. Legacy TDM Pro Tools (e.g. Pro Tools 10 HD with a TDM hardware) uses 48 bit fixed point mixer.

Session file formats are all to do with dynamic range in the content file, they affect nothing to do with how the data is processed in the mixer or plugins.

---

If somebody believed that dithering a signal at 24 bits was important then absolutely the fact that the source for that happens to be 32-bit float is kind of irrelevent. It's just a source able to represent signals lower than the 24th fixed-point bit, and what do you do with that 24th bit and beyond signal as you lose that information? Sure if you believed dithering helps there you would dither it.

The issue is by the the you are down to 24 bits you are pretty much lost in the converter and analog noise floor anyhow--unlike dithering at 16bits for CD. So just don't worry about it.

Re: Dithering from 32 Float to 24 Bit
 

Not dithering 24-bit fixed to 24-bit fixed makes perfect sense

Dithering 32-bit float to 32-bit float makes less sense. And what do they mean by dithering there? It's more complicated with a floating point format. It's a bit of a mystery at least from the documentation. If the belief was the file is heading to a playback system that was going to effectively truncate the exponent off and treat it as 24-bit fixed, then sure dithering makes sense. Worse case the dithering is happening down at the LSB of the Mantissa and likely just irrelevant to most practical uses.

Anyhow something that it may be possible to look at with a very low level signal and some careful playing around if anybody really cared.

For 24-bit fixed at least... Pro Tools won't automatically dither at less than the bit depth. It would be throwing away data for no reason, if you are exporting data at a certain bit depth presumably you want those bits. The dither happens in the least significant bit (which yes might involve changing the next bit up as well, but that's it).

Re: Dithering from 32 Float to 24 Bit
 

No dither when bitrate is not changed makes also sense to me. That’s why it sounds strange to me as they dither 32bit export to 32bit.
But your idea about it makes sense. In the end you can only play through a 24bit DAC so dither would be needed.

I just got confused by the long processing time when exporting 32bit files. So I now go the session folder and just copy the desired file.
Also I usually bounce my masters to a new track and have dither plugin at the last insert, so I can choose the one I like and also check for levels or inner sample peaks while bouncing. After this I also have to copy the final master from the session folder because otherwise additional dither would be applied in every case (exporting to 32, 24 or 16bit). So I also have to use additional software to make my 16bit CD-Files.

The question about “What dither (16, 18, 20bit) is used…” is because Avid dither plugin does not offer 24bit dither. So I think it would be really stupid to apply 16bit dither when exporting to 32 or 24bit.