Dithering in 2024

I have been told that the drawbacks of dithering twice are less audible than truncation distortion.

I smell a fight brewing!

So to get this straight.

If I’m going out from Cubase on my stereo mix bus at 24bit to my HEDD 192 da > analogue mix bus chain > HEDD 192 ad > Cubase to record the HEDD output as a mix.

I add 24 bit dither to the stereo mix bus before it leaves Cubase into the HEDD 192 D/A?

Is that correct?

Download this if you haven't. I believe it was a discussion on this forum that mentioned it:

www.stillwellaudio.com/plugins/bitter/

That's foolproof. You just insert it and it tells you how many bits you're at. If you're over the amount you want to output to a converter or a bounced file, just insert a dither plugin.

Huh? Totally don't understand this. 

If your running a 32 bit session for whatever reason, I guess the first question is are the converters passing a true 32 bit signal to the DAW? 

Or, are your 24 bit converters writing a 24 bit signal the to DAW and the software is filling in the missing bits with zeros? 

Or are you after some other totally different thing? Again don't really understand where your coming from... but none of this is "kind of sort of like" - everything under discussion is also under the rules of hard math & laws of physics. 

I didn’t think a whole lot of converters can actually capture at 32 bit. Maybe it’s becoming more common? I read something about Mytek offering it.

They just take a fixed point signal and scale it with two AD converters to prevent people from clipping them but even then you can still clip the analog front end

I was told in the early days, that it wasn’t about bit depth, one should simply use dither any time a Codec, in other words anytime you are changing from the internal processing.

So this is my question. When DAW is being internally processed at 32bit or 64bit floating, does that get dithered by plugins like Pipeline XT (S1) or Logic's I/O?

Oh...just to see if I can say this here without toxic responses ensuing...

First, as many will be happy for me to say, you might as well dither any linear bit reduction (by "linear", I'm not yet addressing encoding to lossy formats such as mp3). Silly not to, you're exporting anyway, and you'll stave off the potential of an obnoxious form of distortion.

A little more info that will set some people off: When exporting, we really only reduce to 16-bit, or from floating point to 24-bit these days. At 16-bit, the threat is real, at 24-bit it's not, but just dither that export in either case and don't fret.

As for possible downside: For 16-bit, the added noise floor of dither is very slight, next to impossible to notice without "cheating" to hear the difference (cranking a quiet passage to compare with/without), but it removes the possibility of the far-worse truncation distortion. Dither it. For 24-bit, it doesn't matter either way—impossible to hear either the added noise from the dither, impossible to hear the truncation distortion. The noise floor of any DAC or power amplifier ever made, or yet to be made, dwarfs either.

So, if I say "do it anyway", why make people mad and tell the truth that it doesn't matter at 24-bit? Because sometimes it's not so easy to dither, and trying to "do the right thing" (as perceived) has a much larger chance of making a mistake and making the signal worse. So, I believe people should understand, and make the choice for themselves, and be get unnecessarily frightened into doing something that can't possibly matter. Mainly, that case comes up when people who are recording and mixing audio material in a computer like to "send" channels out to external analog processing gear—vintage compressors, for instance, on drums and vocals. Usually it's just a few, but in one case of someone asking, they needed to send to every channel of a large-format mixer, which would require 48 instances of dither plugins running on their computer.

As for mp3 and the like, feed the converter what it needs. I think in most cases that's 32-bit flat these days—float never required dither. (Yes, people will even argue this, I'm just answering the question. Choose who to believe, or ask me more about why, if you want to know.) Of course, it you have a "vintage" converter that wants to be fed 16-bit file, dither to 16-bit first. But...just get a modern converter. 

I'll just give the most basic reason dither at 24-bit doesn't matter, though there are more reasons. And people who aren't physicists or electrical engineers have a really rough time with this one: It's not possible to make a 24-bit converter at audio levels. We don't make 24-bit converters because we need them or because we are capable of making them. We make them because 24 is one byte more than 16.

Basically, pro (+4 dBu balanced) max level is 4 Vrms, consumer (-10 dBV) is 2 Vrms. Let's start with the best case—pro. 24 bits yields 16777216, the smallest step being the reciprocal of that. So, divide 4 Vrms by 16777216 to get the smallest voltage step at full volume: 0.0000002384 Vrms, about a quarter of a microvolt—a fraction of a millionth of a volt. Another way that probably more convenient for audio engineers to look at it is that the bottom bit is about -144 dB from full scale output of the DAC (20 * log10(Power(2,-24)) = -144.49). But if you read specs on DAC (and preamps and amplifiers for the matter), the very best have noise figures at about -120 dB, with a select few inching closer towards -130 but falling well short. That's because even ONE lowly resistor at values required and at audio bandwidths emit noise at around -130, -131 dB. This is thermal noise, called Johnson-Nyquist noise. There are other noise effects down near the bottom of 24-bit, but this is the loudest one and is unavoidable, so we can end the discussion there. And cryogenics is not the answer, because even if the device didn't fail, at some point you'll have to run it into an amp and to speakers and hear it without being frozen to death, in which case it doesn't matter whether the audio is dithered anyway.  BTW, amps are typically far noisier than DACs, because power isn't easy.

I know this is incredibly annoying to some. But I believe if you give people the truth, they can make informed decisions. If that decision is to instantiate 48 dither plugins to "be sure" and feel comfortable, yes, do what makes you feel comfortable. But I would not want to be the guy for whom that just won't work, so I don't do it, but fear all the time that I've damaged the enjoyability of my music for some people because I skipped that step. No, it's not possible to hear the difference—now just do what you want to do.

Also, I've seen someone post, "for years I haven't dithered my 24-bit file because I didn't know about dither—have I screwed my whole library of music??" Personally, I want them to know that they don't need to lose sleep.

Thank you!